Full text of Code of Lighting School Buildings : Bulletin of the United States Bureau of Labor Statistics, No. 382

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U.S. DEPARTMENT OF LABOR
JAMES J, DA VIS, Secretary

BUREAU OF LABOR STATISTICS
ETHELBERT STEWART, Commissioner

BULLETIN OF THE UNITED STATES}
BUREAU OF LABOR STATISTICS ' ' ' '


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SAFETY

CODE

· · No. 382

SERIES

CODE OF LIGHTING
SCHOOL BUILDINGS
ILLUMINATING ENGINEERING SOCIETY
AMERICAN INSTITUTE OF ARCHITECTS
JOINT SPONSORS

--AMERICAN STANDARD
Approved June 16, 1924
American Engineering Standards Committee

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FEBRUARY, 1925

WASHINGTON
GOVERNMENT PRINTING OFFICE
1925


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ADDITIONAL COPIES
OF THIS PUBLICATION MAY BE PROCURED FROM
THE SUPERINTENDENT OF DOCUMENTS
GOVERNMENT PRINTING OFFICE
WASHINGTON, D, C,
AT

10 CENTS PER COPY

NOTE ON REVISION OF THE CODE
The present code was revised under the rules of procedure of,
and has been officially approved as an "American standard" by, the
American Engineering Standards Committee.
For this purpose, a sectional committee made up of representatives officially designated by the societies and organizations listed
below was formed by the Illuminatin~ Engineering Society and
the American Institute of Architects, Joint sponsors of the code:
American Gas Association.
American Institute of Architects.
American Institute of Electrical Engineers.
American Medical Association ( Section on Ophthalmology).
American Public Health Association.
American School Hygiene Association.
American Society of Safety Engineers.
Eye Sight Conservation Council of America.
Illuminating Engineering Society.
National Association of Public School Business Officials.
National Bureau of Casualty and Surety Underwriters.
National Committee for the Prevention of Blindness.
National Council on Schoolhouse Construction.
National Education Association.
National Electric Light Association.
National Safety Council
United States Bureau of Education.
United States Bureau of Standards.
United States Public Health Service.
Women's Bureau of the United States Department of Labor.

ILLUMINATING ENGINEERING SOCIETY
The Illuminating Engineering Society was organized in 1906 for

" * • • the advancement of the theory and practice of illuminat-

ing engineering and the dissemination of knowledge relating thereto."
The society now has about 1,400 members who are interested in the,
subject of lighting from various standpoints : Engineering, economic,
hygienic, aesthetic.
The society has no affiliations with any commercial organization.
Anyone interested in its objects may become a member.

AMERICAN INSTITUTE OF ARCHITECTS
The American Institute of Architects is the national or~anization of the architectural profession. Its objects are to orgam.ze and
unite in fellowship the architects of the United States, to combine
their efforts so as to promote the aesthetic, scientific, and practical


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IV

efficiency of the profession, and to make the profession of ever increasing service to society.
Every architect who is qualified to practice the profession of
architecture and who deals honestly with his brother architect and
with those whom he serves is eligible to membership.
The office of the secretary, the headquarters of the institute, is in
the Octagon House, Washington, D. C. The office of the Scientific
Research Department of the Institute is at 19 West Forty-fourth
Street, New York City.


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CONTENTS
Introduction __ · _ _____ ___ __ __ ___ ___ ___ _______ ___ __________________
Explanation of technical terms______________________________________
I. The rules.
PART
PART II. Why the fulfillment of the rules is important.
PART III. How to comply with the rules.
Rule

1.

2.
3.
4.
5.
6.
7.
8.
• 1,

1,

General requirements ___________________________ _
Illumination required ___________________________ _
Avoidance of glare ______________________________ _
Distribution of artificial light ____________________ _
Color and finish of interior _______________________ _
Switching and controlling apparatus ______________ _
Exit and emergency lighting _____________________ _
Inspection and mamtenance _____________________ _
Blackboards ___________________________________ _
2, 3, 4. Natural light ____________________________ _
Windows _______________________________ _
Lighting value of a window _______________ _
Window shades __________________________ _
Light courts _____________________________ _
2, 3, 4. Artificial light ___________________________ _
Lighting systems ________________________ _
Design of a lighting installation ____________ _
Selecting a luminaire _____________________ _


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Part I
p~

3
4
4
4
5
5
5
5

1, 2
2, 3

Part II Part III
page

page

5
6
6
6
6

26
29
30
30
30

7
7
7
8

8-11
8

10
11

11
11-29
12
15
24
V


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BULLETIN OF THE

U.S. BUREAU OF LABOR STATISTICS
N0.382

WASHINGTON

FEBRUARY, 1925

CODE OF LIGHTING SCHOOL BUILDINGS
INTRODUCTION
In 1918 the Illuminating Engineering Society prepared a.n.d issued a code of lighting school buildings. Shortly after the publication of the code, the New York State Department of Education
adopted it as a guide in planning the artificial lighting of school
buildings in that State. The Industrial Commission of Wisconsin
used the code as a basis for the preparation of the Wisconsjn
School Lighting Code, effective 1921. A number of provisions of
the code have been incorporated in building codes in several States
and municipalities.
Improvements in lightin~ practice during the past five years
have made necessary a revision of the code to conform with modern
standards; moreover, there has been a demand for more definite and
detailed specifications than those contained in the 1918 code.
The accompanying code aims to meet this demand and is intended
to serve not only as a guide for legislators, State and municipal ·departments of instruction, and other regulatory bodies interested in
the formulati~n of enactments, rules, and re~lations for the daylighting and artificial lighting of school buildings, but also as a
guide to architects in planning the lighting of school buildings and
to school superintendents and other school authorities in bettering
lighting conditions. A popularized brief of the code, now in course
of preP.aration, is intended to serve as an aid to teachers in instruct. ing children in the proper use of the eyes and in the underlying principles of correct lighting-an important part of the course in school
hygiene that has received as yet but scant attention.
The subject matter of the code as here presented is divided into
three parts: (1) Rules; (2) Why the fulfillment of the rules is important; (3) How to comply with the rules.
The code was frepared oy a sectional committee consisting of
representatives o organizat10ns, societies, and indivi~uals identified with the school-lighting problem in one or another of its various
phases. This sectional committee was organized by the Illuminatm~ Engineering Society and the American· Institute of Architects,
jomt sponsors for the code, under the rules of procedure of the
American Engineering Standards Committee. The code has been
approved by the sect10nal committee, the Illuminating Engineering Society, and the American Institute of Architects.

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2

CODE OF LIGHTING SCHOOL BUILDINGS

.Although the rules and recommendations of the code are based
upon what is considered the best practice of the present time, it is
~robable that in the future modifications may become desirable as
the art develops and as experience is gained in the a.pplication of the
code.
,
The subject of fire hazard in school buildings, though outside
the scope of this code, should receive most careful attention. Building codes and local, State, and National regulations should be consulted. In this connection reference should be made to the following
pamphlets issued by the National Fire Protection Association, Boston, and promulgated as the regulations of the National Board of
Fire Underwriters: " National Electrical Code," "Installation,
Maintenance and Use of Piping and Fittings for City Ga.st "Installation and Operation of Acetylene Equipment," "Gasoline Vapor
Gas Lighting Machines, Lamps and Systems." The subject of
sa.fety from fire has received special attention in the school-exits section of the American Engineering Standards Committee's Building
Exits Code, which should also be consulted.
Constructive criticism, suggestions, and inquiries in relation to
the Code of Lighting School Buildings will be welcome and should
be addressed to the Sectional Committee on School Lighting Code,
American Engineering Standards Committee, 29 West Thirty-ninth
Street, New York City.
EXPLANATION OF TECHNICAL TERMS

In the rules and discussion of the code it is necessary to use
some technical terms referring to the measurement of light.1 .All
such measurements are now based on standard lamps kept m the national standardizing laboratories of the various countries. The ·candlepower of these standards is fixed by international agreement, and
other lamps are measured by comparison with them. The unit of
candlepower is substantially the average intensity of the old standard sperm candle.
·
Every :practical source of light has different candlepowers or intensities m different directions, and consequently "candlepower"
is not a direct .indication of the total light ~iven out. In order to
avoid ambiguity it has become customary m this country to rate
lamps in terms of their total light output. The unit used is the
lwmen, The lumen is the light falling upon an area of one square
foot all points of which are one foot distant from a source having
an intensity of one candle. Such a surface receives an uwmination
of one foot-cmndk; in other words, one lumen of light flux is enough
to furnish one foot-candle of illumination on 1 square foot. The
lumens needed on a working surface are the product of the number
of square feet of area to be lighted by the number of foot-candles
· reqmred on the surface. The light output of an illuminant, as well
as the 'light received on a given area_ may be mea.sured in lumens.
1 Formal and precise definitions of such terms are given in the reports 6f the Committee on Nomenclature and Standards of the Illuminating Engineering Society,· which

ean be obtained from the office of the society, 29 West Thtrty-mnth Street, New York .
City.


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CODE OF LIGHTING SCHOOL BUILDINGS

8

No lighting installation can throw upon the working surface all
the light produced. The coeffecwnt of utilwation of an installation
with reference to a given plane is the ratio of the light flux (lumens)
received on that plane to the total flux from the lamps illuminating
it.
The rie-fl,ecmon,-factor of a surface is the ratio of the light flux reflected from the surface to the flux falling on it. Reflection may be
regular, diffuse, or a mixture of the two.
Bri.ghtneaa as used technically means exactly what it does in
common speech; that is, the intensity per unit of projected, or
apparent, area of the source. The .brightness of a surface may be
due either to the light emitted by it or to the light reflected by it
and may be measured in various units; but in this code brightness
values are stated in candles per square inch.
A '/;u;mino,4,re is a complete lighting unit consisting of a lightsource, together with its direct appurtenances, such as globe, reflector, refractor, housing, and support. The term is used to designate
completely equipped lighting fixtures, wall brackets, portable lamps,
or so-called removable units.

PART L-RULES
General requirements.
When in use durin$' daylight hours, rooms in school buildings in
which pupils are reqmred to study or do a.ny work shall be provided
with natural light in aecordance with the following rules.
When in use during :eeriods when natural lighting fails, rooms in
school buildings in which pupils are required to study or do any
work shall be provided with artificial, light in accordance with the
following rules.
When in use, other rooms in school buildings, also school
grounds, shall be provided with natwral, O'I' arliftciol, light in accordance with the :following rules.
Rule 1. Illumination required.
The illumination-natural or artificial-maintained shall be not
less than the minimum values in Table I. Values recommended for
ordinary conditions of artificial lighting are presented in the last
column. Higher values are often desirable.
22194°:...-25--2


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4
TABLE

CODE OF LIGHTING SCHOOL BUILD·INGS

I.-Mmimum values of illumination required. and. values recommended
for artificial lighting
Minimum
required
footcandles

Recom•
mended
footcandles

ON THE SPACE 1

Walks, drives, and other outdoor areas, if
used at night •....••• ·-·-·--···-··-·-·-----Playgrounds, outdoor, if used at night ___ ._._
Playgrounds, outdoor, if used at night for
, baseball, basketball, etc ____•-------·-------Storage spaces, passages, not used by pupils __
Boiler rooms, power plants, and similar
auxiliary space.~- ___________________________
Stairways, landings, corridorstoaisles, exits,
elevator cars, washrooms, ilets, locker
spaces, dressing•rooms ______________________
Recreation
rooms, gymnasiums, swimming•
pools_______________________________________

0.1
.5
5
.25

0.5
2
10
2
3

1

3

3

7

ON THE WOEK 1

Auditoriums, assembly rooms ________________
Auditoriums, assembly rooms, etc., if used
for class or study purposes _________________
Classrooms, study rooms (desk tops) _________
Classrooms, study rooms (charts, blackboards) ____________________________________
Libraries (reading tables, catalogues) _________
Libraries (bookshelves, vertical plane) _______
Laboratories (tables, apparatus) ______________
Manual training rooms; workshops, etc ______
Drafting rooms, sewing _______ • ______________

2

3

~

10
10

5
3
5
3
5
5
8

6
10
6
10

10
15

· 1 Where the space or work is not clearly evident, as for instance in an auditorium, the illumination may
be measured on a horizontal plane 30 inches above the floor. However, where the space or work is clearly
evident, such as stair steps and desk tops, the illumination shall be measured on the plane of the steps and
desk tops, respectively.

Rule 2. Avoidance of glare.

Lighting whether natural or artificial shall be such as to avoid
harmful glare, objectionable shadows, and extreme contrasts.
Bare light sources, such as exposed lamp filaments, gas
mantles, or bright sky areas located within the ordinary field of
vision are presumptive evidence of harmful glare. Seating shall be
so arranged that pupils are not compelled to face windows. For
specifications of definite requirements under this rule refer to
Part III.
Rule 3. Distribution of artificial light.
Lamps, reflectors, or other suitable accessories shall be of such
light-distributing character and shall be so il!.stalled in regard to
mounting height, location, and spacing as to avoid excessive variation in illumination upon workplaces. In a classroom at the desk
tops the ratio of the maximum intensity of artificial illumination to
the minimum intensity of artificial illumination, measured in footcandles, shall be less than 4.
Rule 4. Color and finish of interior.
In rooms in which close visual application is necessary, walls
shall have a reflection factor within the range from 30 to 50 per cent.
Ceilings and friezes ( the latter in the case of high ceilings) shall
have a reflection factor of at least 65 per cent. Desk tops and other
woodwork shall have a reflection factor not exceeding 25 per cent.


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CODE OF LIGHTING SCHOOL BUILDINGS

5

In corridors and halls, ceilings and walls shall have a reflection
factor of at least 50 per cent. Dadoes and blackboards are obvious
exceptions. Glossy finishes shall be avoided wherever they are Jikely
to cause glare. The preferred colors for walls are light warm gray,
light buff, dark cream, and grayish green; for ceilings and friezes,
white and light cream.
The nosing of treads on all stairs used as exits should be such as
to show the edge of each step by contrast when viewed as in
descending.
·
Rule G. Switching and controlling apparatus.
Switching and controlling apparatus shall be installed at each
point of entrance to school buildings, also in c~assrooms, basements2
hallways, and stairways, also wherever required in other parts ot
buildings. Rooms having several entrances require such equipment
only at the principal entrances.
Rule 6. Exit and emergency lighting.
Artificial lighting to be provided under rule 1 in all stairways
and exits and m the passageways appurtenant thereto shall be supplied preferably from an mdependent source or from a connection
extending back to the main service entrance for the building so that
failure of room lighting from internal causes will not affect the
exit and emergency lightmg. In case of unusual danger which may
exist on account of trpe of building, nature of the work, crowded
conditions, or lack of suitable exit space, an independent service
shall be insured by connecting to a separate source of supply without
or within the building.
Classrooms and auditoriums during stereopticon and motionpicture exhibitions may be dimmed. After dark, if more than 50
persons are gathered in rooms having an illumination less than 0.1
foot-candle, the exits from rooms and all passages to the exits of the
building shall be indicated by adequately illuminated exit siwis, so
as to clearly indicate the paths of safe exit from the building in
case of emergency.
Rule 7, Inspection and maintenance.
All parts of the natural and artificial lighting systems, including
windows1 skylights, lamps, luminaires, walls and ceilings, shall be
systematically inspected and properly maintained and cleaned so as
to assure illumination levels indicated in rule 1.
Rule 8. Blackboards.
Blackboards shall be illuminated and located with respect to light
sources so as to avoid glare. The surface of blackboards shall be
made and kept as dull as possible. Blackboards shall not be located
in the same wall with windows.

PART II.-WHY THE FULFILLMENT OF THE RULES IS
IMPORTANT
General requirements.
Examinations of thousands of school children, extending over
many years, have shown that a considerable proportion suffer from
defects of vision-the result largely of continued use of the e:yes in
close work under unhygienic co~ditions. It !$ well established that

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OODE OF LIGHTING SCHOOL BUILDINGS

defective vision is often progressive and is therefore found to a
greater extent among older children.
It is found that, m general, children with defective vision are
retarded in their :progress in school work They also enter upon
their life work seriously handicapped.
The severe requirements imposed upon children's eyes by modern
educational methods create need for the best of workmg conditions.
Among these conditions lighting is of primary importance. Improper and in'adequate lighting causes eyestrain, resulting in functional disorders, nearsightedness, and other defects of the eyes to
which the immature eyes of children are especially susceptible.
Schools require a high standard of illumination, because immature eyes are more susceptible to injury than those of adults, and
learners must necessarily apply their: eyes more continuously than
older persons who have acquired skill through repetition.
It is, therefore, essenti'al that the lighting of school buildings, both
natural and artificial. should conform to the· requirements specified
in the code.
Rule 1. IDumina.tion required.
Definite minimum intensities of illumination on the work places
are specified for the conservation of vision. In halls, stairways,
passages to exits, etc., adequate intensities are imperative for safety.
In addition to the benefits derived from lighting of the levels specified, the desirable effects of cheerful interior surroundings 'are obtained. These minimum intensities are the least permissible considering all the factors involved. From the standpoint of best vision
much higher intensities are advantageous.
Rule 2. Avoidance of glare.
Glare is objectionable because it tends to injure vision and to disturb the nervous system; it causes discomfort and fatigue and thus
reduces the efficiency of the student; it interferes with clear vision
and increases the risk of accident. From both the humanitari'an
and economic viewpoints glare should be avoided. ·
Glazed paper reflects light somewhat like a mirror and introduces glare due to images of light sources reflected from it. The
use of unglazed paper 'and suitable type promotes the conservation
of vision.
Rule 3. Distribution of artiftcial light.
A substantially uniform intensity of illumination at work places
provides equal advantages for all students. Light reaching any
particular point at 'a work place from a number of sources, such as
1s implied in rule 3, reduces the harshness of shadows. General
lighting eliminates the probability of improper direction resulting
from the use of a very predominant light source.
Rule 4. Color and finish of interior.
Walls are within the field of vision a considerable part of the
time.· A moderate reflection ·factor with dull surfaces assures comfortable brightness contrast. Inasmuch as walls are juxtaposed to
blackboards a moderate reflection factor of the walls assist in reducing the brightness oontrast betw~en these surfaces.


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CODE OF LIGllTING SCHOOL BUILDINGS

Luminaires are more comfortable to view when seen against
light backgrounds. Ceilings and friezes having a high reflection
.factor provide for this and increase the efficiency of the lighting
system.
Glossy finishes and glass surfaces reflect bright images of
windows and artificial light sources, thereby contributing to visual
discomfort.

Rule G. Switching and controlling apparatus.
Switching and controllin~ apparatus properly located is necessary
in order that artificial lightmg may be properly controlled and used,
and th~t persons may proceed in safety from point to point in a
building.

,

Flail lateaslty

6

6

s

$

Final lntollliry

9
~

4

~

e

l

'

- - - .~;:·:)· .
fntenslt,.as founcl

2

. ___
._

CASEJ

CASE II

Occulonat r.taint.nan«

No M.aintenance

s

·/::•·}.
,.J.> ...

;·.··-

---1

CASE Ill

:::itl.,::.!.n::;

FIG. 1.--Chart showing the importance of prompt renewal of bnmed-out lamps and systematic cleaning of lighting equipment. Tests on semi-indirect and indirect lighting
systems

Rule 6. Exit and emergency lighting.
Emergency lighting makes for the reduction of accidents and
hazard. Building codes should be consulted for local requirements
covering exit lights. (See reference to fire hazard in the introduction.)
Rule 7. Inspection and maintenance.
Walls and ceilings darkened by smoke and dust, dirty windows
and skylights, grimy reflectors, blackened lamps, or broken mantles,
or lamps of incorrect size or voltage, will render even a well-designed
lighting system ineffectual. The value of regular inspection and
maintenance is diagrammatically illustrated in Fig. 1. In each of
these cases the failure to observe simple maintenance requirements
resulted in an unnecessary economic loss.
The decrease in illumination due to these causes is often so
~adual that it is not noticed. Inasmuch as the levels of artificial
illumination now in use are so low any considerable decrease in


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8

OODE OF LIGHTING SCHOOL BUILDINGS

illumination is almost certain to interfere more or less with vision.
The illumination intensities in Table I are values to be maintained.
Rule 8. Blackboards.

Unless properly illuminated and located with respect to light
sources, blackboards in combination with the other conditions are a
source of eyestrain. Pupils are often required to look at blackboards
for long periods of time; hence it is important that the best conditions be provided. Blackboards with dull surfaces reduce the annoyance of reflected images and facilitate reading the markings thereon.
In order to avoid excessive brightness contrast, which is trying
to the eyes, blackboards should not ~ placed on a white o:r; highly
reflecting wall.
The location of blackboards between windows introduces a bad
visual condition due to contrast with adjacent bright areas.

PART 111.-HOW TO COMPLY WITH THE RULES
The following sections discuss in detail the ways and means of
providing adequate and proper lighting as required by the rules
of this code.
Rules 1, 2, 3, and 4. Natural light.

One of the established rules for proper lighting of desks from
windows in walls is to have the dominant light come from the left
side. Most authorities on daylighting advocate wnilateraJ lighting;
that is lighting by windows located on one side of the room only,
especially for classrooms (see Fig. 3). This method of lighting IS
recommended where the width of the room does not exceed twice the
height ot the top of the window from the floor.
.
Rooms of unusual width, such as auditoriums, may have windows on the right and left sides. However, where cross shadows are
objectionable, windows at the left and rear are preferable.
.An eastern exposure is generally considered to be the most desirable for classrooms and a northern exposure the least desirable.
Lighting by overhead sources of natural illumination, although
sometimes used for assembly rooms, auditoriums, and libraries with
relatively high ceilings, has but little application in classrooms.
When overhead sources of natural illumination are used the light
should come from a north skylight or saw-tooth construction oriented
to exclude direct sunlight.
To secure the highest lighting values in a side-lighted room it
is recommended that the room be so desiS'lled that no work space
is more distant from the window than twice the height of the top
of the window from the floor.
The sky as seen through a window or skylight is a source of glare.
For this reason the seating arrangements should always be such
that pupils do not face windows or skylights.
Windows.-Tests of daylight in well-lighted school buildings indicate that in general the window-glass area should not be less than
20 per cent of the floor area. As the upper part of the window is
more effective in lighting the interior than the lower part, it is


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9

CODE OF LIGHTING SCHOOL BUILDINGS

A

'

:-----i
I

I

I

: -- e-I'
I

I
I

:

,_____ JI

s:-

e_LEVATION

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0

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ELEVATION

,_ _ _ _ _ _ _ _ _ )

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!\

~ I

f./, ,,~
(i

FIG. 2.-Diagrammatic illustration or glare from blackboards: (a) Showing that occupants of seats In shaded area are subjected to daylight glare from blackboards. (b)
Showing angles at which glare is experienced from daylight and from artificial light.
( c) Arrangement of local artificial lighting to minimize glare


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10

CODE OF LIGHTING SCHOOL BUILDINGS

recommended that the top of the glass be at no greater distance
than six inches below the ceiling. The sills of side windows should
be not less than 3 feet or more than 4 feet above the floor. No
direct light should reach the eyes of seated pupils from below the
horizontal.
Lighting value of a window.-The lighting value of a window
at any given locati,on in the room, will depend primarily upon the
brightness of the sky, the amount of sky visible through the window
at the given location in the room, and secondarily upon the reflection factor of the surroundings and the dimensions of the room.

a 0□□□□□□□□□
0
0

DODD □□□□□□

a □□□□□□□□□
a 3:l□□□□□□□□□
t{
0

ODD □□□□□□□
/,l

1Nl)1C. ..Tl.$

C&ILIIIG •OIITLI.T

l"Oll

AllTll'IC:.IAL

1.IG;HTIMO,

FIG. 3.-Elevation and plan of a classroom illustrating the position of outlets and lumlnaires of a direct 1.ighting system ; alRo showing a good afrangement of windows for
natural lighting. In recent practice the width of room varies from 22 feet to 25 feet,
the length from 28 feet to 32 feet, and the height from 12 feet to 14 feet. If the
architectural design permits, it ls preferable to increase the glass area by extending the
windows as near to the rear wall of the room as possible

Observations in well-lighted schoolrooms having a comparatively unobstructed horizon show that under normal conditions of'
daylight satisfactory illumination is usually obtained when the
visible sky s-o.btends a minimum vertical angle of 5° at any workplace of the room. It is recommended that a sky exposure for any
pupil's desk in the room be at least 50 square degrees, preferably
about 5 degrees vertically and 10 degrees horizontally.
This
should be borne in mind when selecting sites for new buildings inasmuch as the proximity of adjacent buildings may seriously interfere with the natural lighting.
.

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CODE OF LIGHTING SCHOOL BUILDINGS

11

Window shades.-.Although direct sunlight is desirable in interiors from a hygienic standpoint, it is often necessary to exclude or
diffuse it by means of window shades. Shades should perform
several functions such as the diffusion. of direct sunlight; the control of illumination to secure reasonable uniformity; the elimina.tion of ~lare from the visible sky or from bright areas outdoors,
such as light courts, or adjoining buildings; and the elimination of
glare from blackboards.
These requirements can be met by a number of arrangements,
several of which have been found satisfactory and eJlsy to maintain.
For instance, windows can be equipped with two shades operated on
two rollers. These can be arranged with both rollers at the middle
of the window, one operating upwards and the other downwards, or with one roller at the middle and one at the bottom, both
operating upwards. Shades so placed may be operated independently, thereby facilitating the shading and diffusion of the light.
Instead of two shades a single· shade can be used with a device
that permits the roller to be placed at any position on the window.
Such a shade can be so placed that the light will come in from the
top of the window and will be shut out from the lower portion, or
will come in from the top and the bottom and will be shut out from
the middle portion. .Another way of controlling the light is to use
a translucent shade, which unrolls from the top, down, and an
opaque shade which unrolls from the bottom upward. Since
it is the top portions of the windows which supply, the illumination to the spaces in the room farthest from them, it is bad practice
to cut out light by pulling down the shade from the top more than
is absolutely necessary. Pulling down a shade from the top also
interferes with ventilation when windows are lowered from the top.
The material of the shades should be sufficiently translucent to
transmit a considerable percentage of the light and at the same
time diffuse it. Their color should be such as to harmonize with the
interior decorations of the room. .A translucent shade transmits a
considerable amount of light, hence care should be taken that this
transmitted light not only harmonizes with the color of the room
but meets visual requirements. .A light tan or a light buff material
will, in general, be satisfactory. With such shades it is possible to
exclude all direct sunlight and at the same time to permit a considerable amount of light to reach the ceiling, which light in turn is
diffused throughout the room.
Shades should be wide enough to cover the window and to extend over each side of the window frame so as to prevent direct
light from passing_ its edges.
Light courts.-Reflection of light from the walls of courts or
other exterior walls is often very helpful in increasing interior
illumination. Hence the nearby walls which are visible through
the windows should, as a rule, have high reflection factors. Care,
however, should be taken to avoid glare.
Rules 1, 2, 3, and 4. .Artiftcial light.
In the consideration of how rules 1, 2, 3, and 4 can be com:{>lied
with in artificial lighting, the subjects of illumination intensities,
avoidance of glare, distribution of light on the work, and color and
22194 °'-25---3


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12

CODE OF LIGHTING SCHOOL BUILDINGS

finish of the interior are so closely related and interdependent 'that
it is thought advisable to discuss the four subjects together. This
will be done first by describing the different forms of lighting
systems and the characteristics of each; ·second, by giving the details
of the design of a typical schoolroom lighting installation, choosing
for sake of brevity one popular and recognized method of lighting;
and third, by indicating the salient points which should be stressed
in the selection of the luminaire. The capacity of the wiring installed should be ample to provide for the illumination recommended
in the last colutnn of Table I, even though cost considerations may
make it seem desirable to employ a lower level. The additional

FIG. 4-0pen-bottom dirrect·llghtlng
lumlnaire.

FIG. 5-Inelosed prilllD8.tlC directlighting 111D1ina1re.

cost of such wiring is slight compared with the cost of reconstruction.
LigJ,;tinv B'!JBtema.-In general there are three distinct systems of
artificial lightin~, namely; direct, semi-indirect, and indirect. These
names are descr1ftive and designate broad classes of Ughting, the
boundary lines o which are indefinite.
The direct-ligl,;ting B'!JBtema deliver at least half of the light below
the horizontal so that the dominant light on the work places is
received directly from the luminaires. Such systems may be divided into two groups; the direct-lighting system employing openbottom luminaires and the direct-lighting system using inclosed
and semi-inclosed luminaires.
An open-bottom luminaire direct-liglwilfl,g ay/ftem is one in which
the dominant light reaches the work places directly from the

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CODE OF LIGHTING SCHOOL BUILDINGS

13

luminaires which are open at the bottom and in which the light
source may be seen from below. Such a. lighting system may be
further classified as local or general. In the former the luminaires
are placed close to the work and illuminate a very limited area;
in the latter they are installed overhead in such a way as to
iJluminate the whole room area as well as the limited area upon
which the work is done. An inclosed luminaire is one in which the
light source is completely surrounded by the globe and holder.
Some luminaires (sometimes termed semi-inclosing) having open or
clear glass spaces in conjunction with diffusing glass, opaque reflecting surfaces, etc., may be considered from the standpoint of
lighting to belong to the direct-lightini class.
A semi-indirect system is one in which an appreciable :portion of
the light reaches the work place directly from the lumina1re, but in
which more than half of the light is directed to the ceiling and upper

-DIFFUSING

GLASS

FIG. 6.-Semi-indirect lumlnaire
Unclosed)

•FIG. 7.-Inclosed difl'using-glass directlighting luminaire whose shape is a composite of several commercial shapes

walls ·and thence reflected to illuminate the work places. A semiindirect luminaire usually consists of a lamp equipped with a diffusing bowl or inverted glass reflector, as illustrated in Figs. 6 and
8. The relation between the relative amounts of light above and
below the horizontal through the light center of such a unit de~nds
largely upon the character of' the transmission of the bowl. When
the glass bowl or inverted reflector of the ae1T1Arindirect luminaire
has a high transmission, the illumination approaches that of direct
lig-hti"![l, and when of low transmission the effect approaches that
of indirect lig-hting.
·
A totall;y indirect-lifikting systMT1, is one in which all of the light
reaches the work indirectly after reflection from the ceilings and
walls. The luminaire usually consists of a. light source equipped
with an opa.que bowl or inverted reflector, as illustrated in Fig. 9.
Direct-lighting systemlJ. The open-bottom luminaire is subject
to criticism even though the light sources are shielded from the


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14

CODE OF LIGHTING SCHOOL BUILDINGS

normal angle of vision because of the harshness of shadows and the
glare due to reflected images of li~ht sources from shiny paper
textbooks and polished desk tops. Diffusing-bulb or bowl-enamelled
lamps or frosted inner cylinders for gas effect a considerable improvement when used in this type of luminaire. Ona of t4e chief
advantages of this type of equipment is its relatively high efficiency.
The inclosed luminaire, when made of a good diffusing glass and
of sufficient size to insure low brightness of both the luminair.e and
reflected images, produces satisfactory lighting results from the
standpoint of shadows and glare. Furthermore the coefficient of
utilization is high. The depreciation due to the collection of dust
and the resultant loss of light are less than in most systems. Partly
because of economy, the inclosed unit is one of the practicable
solutions of school-lighting problems. It is generally advantageous

+-DIFFUSING

GLASS
M1Pf1't01ft1>-GLtfH

FIG. 8.-Semt-lndlrect lumtnalre
(open)

o,r-------

ltRcnRIN- £#11/11161.

FIG. 9.-Indirect lumtnatre

t.o select glassware havin~ the horizontal dimension large as com-

pared with the vertical dimension in order to obtain a satisfactory
utilization of light.
The Be-mi-indirect 8'f/Btem employing ~d diffusing glass, of sufficiently low transmission to insure low brightness, provides excellent lighting. Inasmuch as this system employs the ceiling and
upper walls for redirecting a large part of the light reaching the
work place, these surfaces should have fairly high reflection factors.
For this reason these surfaces ·should be properly maintained.
When used in smoky or dirty environment very material losses in
the illumination result unless frequent cleaning is adhered to.
The itndirect B'!fBtem provides excellent lighting ~s characterized
by the desirable qualities of ,zood distribution, absence of strong
· shadows, and low surface brightness. .As in the case of the semiindirect luminaire, ceiling, upper walls, and the luminaire require


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15

CODE OF LIGHTING SCHOOL BUILDINGS

~uent cleaning in order to maintain the illumination intensity
-for which the installation was designed. For a comparison of the
coefficient of utilization of these three systems see Table III.
Design of a lighting imtallation.-The subject is too involved
to be handled in a short treatise unless limitations are set on the
scope of the discussion. These considerations therefore will be confined to the design of a lighting installation for a classroom 32 ·feet
by 24 feet with a ceiling lieight of 12 feet, the ceilll).g having a
reflection factor of 70 per cent and the walls having a reflect10n
factor of 5_0 per cent.
To comply with rule 2 on ·the ~'Avoidance· of glare" it is necessary to diffuse and redirect the light proceeding from the filament
or mantle. To comply with rule 3 on " Distribution of light " it is
necessary to specify the number of lamps, their size, S,Pacing, hanging height, etc. Rule 4 on, " Color and finish of interior" plays an
important part in this discussion.
. .
For the sake of simplicity and brevity a typical lighting installation, employing totally inclosed diffusing luminaires, will be
discussed.
·
The factors which should be considered in determining-the size
and number of lamps to be used in a given room are: First, the illumination in foot-candles to be supplied; second, the floor area, which
in this case is 32 feet by 24 feet or 768 square feet; third, the amount
of light in lumens emitted from each lamp obtained from Table II;
fourth, the coefficient of utilization of the lam:ps and their accessories
as installed in the room. The last quantity mvolves many factors,
such as the relative dimensions of the room. the reflection factor
of the surroundings, the number and character of luminaires,
their locations and han~ng height. In Table III coefficients of
utilization for modern lighting equipment are given for a typical
standard classroom. These values refer to the initial instaflation
lamps and
without any allowance for depreciation due to aging
dust collection. The plane of the work in this case is the desk tops,
generally 24 inches aliove the floor.

of

TABLE 11.-Lumit&OUB ftua: emitted: Bv gaB-f'-lled incandeBCent tungBten la.m,,11•
[Standard lighting service 110-115-120 volt]
Lamp size (watts)
75 ____________________________________________ _
100_ --- ___________ -- -- --- -- --- -- _-- ____ --- ____ _
150 .. -- _____________ -- ________ -- -- ___ -- _____ -- _
20() ____ - - - - - - - -- ------------------------ --- ---30() __ --- - - - - -- ---------------·----------- -- -- -- .

500____ - --- - -- --- --- --- -- -- --- -- -- --- -- -- -- -- --

750________ --- _- _- _- -- -- _-- -- _-- -- _-- _________ _
1, 00()____ - - - - - - - -- -- - - - -- -- - -- -- - - - - - - - - - - - - - - -

I

Clear lamp
(initlallumens)i
885
1,290
2,145
3,060
4,950
9,050
14,325
20,000

data, while correct at the time of writing, are subject to change.
NOTl!I.-" Daylight" lamps of a given watta~ emit approximately two-thirds the
amount of light emitted by the clear lamp. The ' daylight " lamp is a gas-ftlled tungsten
lamp with a blue-glass bulb pl'oducing light more closely approximating daylight.
1 These


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16

CODE OF LIGHTING SCHOOL BUILDINGS

'

·.

.

.

FIG. ·1 0.-Interior view· of a classroom showing an excellent arrangement of

windows. Note the double shade rollers placed at middle of windows
which permit either the upper or lower part of the window to be shaded
independently
·

FIG. 11.-Poor · daylighting: · Badly placed window openings; blackboards
located between windows
N0TE.-A better arrangement would be to have the four windows on one side and none
in the rear.


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CODE OF LIGHTING ·~

OL BUILDINGS

FIG. 12.-Good daylighting of a school librnry

13.-Bad lighting. The luminaires are hung too low and the light sources
are not adequately shaded. Note that the glossy varnished surfaces add to the
glare

FIG.


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17

18

C@DE OF LIGHTING SCHOOL BUILDINGS

FIG. 14.-Bad lighting. The use of local lightin~ by adjustable table
lamps usually results in glare from lamps on neighboring tables; also
in annoying shadows


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Federal Reserve Bank of St. Louis

FIG. 15.-Bad lighting. The local lamps ff used at all, should
be provided with reflecting shades to protect the eyes from
glare and at the · same time to direct the light to the work

CODE OF LIGHTING SCHOOL BUILDINGS

FIG. 16.--Good general lighting with inclosed Iuminaires

FIG.

17 .-Good general lighting with open bottom reflectors suspended 20
feet above .the floor


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19

20

CODE OF LIGHTING SCHOOL BUILDINGS

FIG. 18.-A school corridor showing natural lighting through transom sash
in the cla:ssroom partitions and ceiling-type luminaires for _ artificial
lighting


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FIG. 19.-Study room equipped with inclosed luminaires

CODE OF LIGHTING SCHOOL BUILDINGS


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Fm. 20.-Good semi-indirect lighting

FIG. 21.:-Good indirect lighting

21

22

CODE OF LIGHTING SCHOOL BUILDINGS
TABLE II.-Lummous ft,u1e emttted-(Concluded):
B11 gas mantle 'burners• at gas pressure of 2.5-inch water column

Number of mantles to each
b~

L - - -- -- -- -- --- -- --- ---- - ---- -- -2_ - - -- --- -- -- --- --- -- ---- -- -- -- -3_ - -----------------------------4_ - - ----------------------------5_ - - --- -- -- -.- --- ----- ----------- 6- - - -----------------------------

Size of
mantles
(lnohes)

I

Gasconsumrction
(cub cfeet

Base
mantle

per hour)

(lu.mens)

3.66

994
1,326
1,978
2,446
3,664

4. 37

6. 71

9.14
10.60
12.10

4,126

B11 gas mantle burners which. Me self-C011,tained • at gas pressure of 2.S-mch
water column

Number of mantles In each
burner

L - -----------------------------L -- -----------------------------

1- - - - - - - -- - -- - -- --- -- --- - ------ --

Size of
mantles
(lnohes)

Mantles
Oas conIn
sumption lnclosed
clear
Klass
(cubic feet cyllnclers
per hour)
(lumens)
2. 21
4.00
8.16

686
866
2,486

t These burners are knmrn as horizontal Inverted burners and are made for use In semi-Indirect lumlnalres.
By combining two or more of these burners In a single Jumlnalre the total lumens available can be Increased
as desired. n 1¾-lnoh mantles are used, 10 per cent Increase in total lumens is available.
t These burners are furnished_ complete with clear inner cylinders and shade or globe holders to take
out.side globes and shades as selected. These are Inverted burners and are used generally as complete
Iuminaires. Semi-lnclosed shades or totally lncJosed globes can be used as desired.

TABLE

III.-Ooetflcien,ts of utiluation for a classroom 82 feet b11 24 feet, ceiling
12 feet high.1
[Reflection factor of celling, 70 per cent)
Reflection factor of
walls

Lighting syetem
60 per cent 30 per cent
DIBJICT LIGHTING

1. High reflection factor open-bottom glass reflectors (see fig. 4) w!th bowl2. P:~~~gunit; clear lamp (see fig 5) _-----------------------------

3.

In~~~t=,hicl~~=~•-~~-~~~~~-t~~-~~~~~~-

0.47
.47

0.43
.42

.39

.34

.33
.37

.29

.so

.27

SBJO•INDmBCT LIGHTING

4. Low
transmission,
high reflection factor glass,bowl
with
clear lamp (see figs. _
6 and
8) _____________________________________
---·______________________
5. Medium transmission, glass bowl with clear lamp__________________________ _

.33

lNDmBC'r LIGHTING

6. Metal, compo or glass bowl containing mirror reflec.or; clear lamp (see fig. 9) _
1 Transactions IDumlnating


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Engineering Society, Vol. XV, No. 2, Mar. 20, 1920.

CODE OF LIGHTING SCHOOL BUILDINGS

23

Computations to determine the proper size of incandescent electric or gas lamps may be made by the use of the following equation:
AI
L=EN
In this equation:
L=the
A=the
I=the
E=the
N=the

lumens emitted by the lamp (Table II)
area of the floor or horizontal work plane in square feet.
illumination in foot-candles (Rule 1)
coefficient of utilization (Table III)
number of lamps required.

The first step in using this equation is tht' determination of the
number of lamps required. From experience it is ascertained that
in order to obtain the desired distribution of illumination. the
light sources in direct lighting should not be spaced farther apart
than a distance of 1.5 times their elevation above the desk tops.
For instance, if the light sources are hung 8 :feet above the desk
tops, the maximum spacing between should not exceed 12 feet in
order that the requirements of rule 3, "Distribution of light,"
may be fulfilled. Now, considering the problem of a classroom (32
by 24 feet) having the minimum ceiling height of 12 feet, we must
first determine the number of luminaires required. The plane of the
work will be that of the desk tops which is a horizontal plane approximately 24 inches above the floor. Then if the luminaires are
installed in ceiling-type fixtures and an allowan~e of 18 inches :for
depth of fixture and globe is made, the elevation of the light
source above the plane of work will be approximately 8½ feet.
Hence the maximum spacing between luminaires must not exceed
12 :feet 9 inches. With a room of these dimensions, six luminaires
therefore would be required, spaced approximately 12 feet apart as
illustrated in Fig. 3. In this example we will assume that an illumination of 10 :foot-candles is desired. We will also assume that a
luminaire of the type listed under item 3, Table III, is chosen
and that the ceiling and walls have reflection :factors of 70 and 50
per cent, respectively. Under these conditions the coefficient of
utilization will be 0.39 ( see Table III). Now applying the formula
weh1we32X24XIO
L = 0 _39 X 6 = 3,282 lumens.
To offset the decrease in illumination due to lamp depreciation
and dust collection on the luminaires the number of lumens required per lamp will have to be somewhat increased. For this a
safety factor should be used which will insure adequate illumination
when the lighting installation shows a maximum depreciation under
the system of cleaning adopted. How much to allow for depreciation, with a given type of luminaire, depends to a considerable extent on the locality and nature of work carried on. Experience
has shown that a factor of 1.3 provides for average conditions if
a schedule of regular and frequent cleanin~ is adhered to. Applying this factor to the problem at hand it will be necessary that each
lamp supply (3,282 by 1.3) 4,267 lumens.
Referring to Table II, lamps :for standard 110-120 volt service,
it will be noted that the JOO-watt lamp is the nearest size of clearbulb gas-filled tungsten lamp which will supply the required lu-


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24

CODE OF LIGHTING SCHOOL BUILDINGS

mens, whereas the nearest size of "daylight" gas-filled tungsten
lamp which will supply the required lumens is the 500-watt lamp.
The nearest size of gas burner that will sufply the r~uired lumens
is two 2-mantle burners consuming a tota of 12 cubic feet of gas
per hour.
The above example is intended solely to illustrate the method of
computation. Estimates of the illumination obtained from an actual
installation may also be made by a similar computation.
Only four outlets are necessary if indirect-lighting luminaires
or semi-indirect luminaires with dense glass bowls a.re. used in a
room of this size. In Table III it is seen that the utilization factor
for semi-indirect lighting with dense glass luminaires is 0.33 for
the same room and conditions used in the previous computation.
Applying the formula we haveL=

32X24 X10
0 _33 X 4 = 5,818 lumene .

.Allowing for depreciation, we have 5,818 multiplied by 1.3 or 7,563
lumens necessary from each of the four light-sources. The nearest
size of clear-bulb electric filament lamp is seen in Table II to be 500
watts. Here a total of 2,000 watts would be used as compared with
1,800 watts in the direct-lighting case, but the illumination intensity
would be slightly greater in the former case. Of course the illumination intensity would be identical in the two cases if it were possible to
obtain lamps of the exact size computed in the two cases.
Sekctir,,g a lwminaire.-It is not possible with bare incandescent
electric or gas lamps to meet the requirements of the school-lighting
code in respect to rule 2, " Avoidance of glare" or economically in
respect to rule 3, "Distribution of light." It therefore becomes necessary to equip the lamp with reflecting. and diffusing accessories.
Far from being a hardship however, this is actually an economy
since the light flux from the unshielded lamp is not distributed in an
economical manner. Efficient reflecting and diffusing accessories redirect the light, thereby increasing the efficiency of utilization considerably over the value obtainable with the bare lamps, irrespective
of the fact that the diffusive and redirect4ig media in themselves
absorb a portion of the light flux. Aside from this, the ability to
utilize the li~ht produced, because of "eye ease" and lack of brilliant
sources withm the field of vision, is noteworthy, and justifies the use
of proper reflecting and diffusing accessories.
· Any of the types of luminaires from 1 to 6, inclusive1 in Table III
will meet the requirements for overhead lighting provided lamps of
the proper-size and type for the particular accessory are employed.
It is particularly necessary to guard against the use of lamps too
large for the reflector or globe in the direct or semi-indirect systems
if rule 2, "avoidance of glare," is to be fulfilled.
The following table shows the sizes of inclosing globes of high
efficiency ( 80 per cent output) good diffusing glassware (through
which the position of the lamp filament can not be ·seen) to be used
with various sizes of clear lamps.
In this table the brightness of the brightest square inch is given
rather than average brightness or some other specification. An
average brightness specification allows wide variations of bright-


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CODE OF LIGHTING SCHOOL BUILDINGS

25

ness between maximum and minimum. In effect two samples of
diffusing glass, one practically uniform in brightness and the other
having a small area exceedingly bright but with the rest of the
globe sufficiently low in brightness to average the same as the first,
could be rated alike although their acceptability from the standpoint of glare could be widely different. For other factors contributing to glare see rule 2, " Avoidance of glare," Part III.
TABLE

IV.-Recommendea globe sizes of high effl,ciency gooa tZiffulling glass
1

2

4

3

Minimumglobe Brightness of brightest
square inch (candles
diameter
Size oflamps
Lamps,
(measnredat
per square inch)
(watts) to be used
lumens
maximum
with (3)
(maximum) width) tobe
used with (1) Zone 35° Zone 70°

75-100•••••••••••..
100-150.•••••••.•••
150-200••••••••••..
300. ...............

1,300
2,100
3,000
4,000

Inchea
12
14
16
18

4. 0
4. 5
4. 5
5. 6

3. 5
4. 0
4.0
5.0

From the utilization factors in Table III, it will be noted that
some luminaires have the advantage of· being more efficient than
others.. This characteristic should be given considerable weight in
the selection of a lighting accessory. However, other items should
be considered, such as the appearance of the lighted room, quality
of light and freedom from glare, reflected glare from images of the
luminaire in J?<>lished surfaces, character of shadows, and ease
and cost of mamtenance.
The characteristics of the luminaires related to these desirable or
undesirable features of a lighting installation are, diffusive ability,
relation between the size of the lam]? and diameter of the diffusive
unit, shape of the unit, correct centermg of light center to secure the
correct surface brightness, and relation between the holder and the
reflecting surface, and the over-all efficiency.
The first point is that of efficiency. Since inclosing glassware
ii- being extensively used in school-lighting systems, some of the
pitfalls which might be encountered m considering this phase of
the question may be pointed. out. Variations in the distribution
curves obtained from individual units of lighting equipment are
sufficient to make it undesirable to place too much dependevce upon
tests secured by measurements of a single luminaire. Purchasers
of the equipment can protect themselves by specifying that illumination measurements made upon a completed installation shall
show values corresponding to the representative luminaire offered
by the manufacturers or installers of such equipment.
To be representative of the efficiency, 10 or ·more globes, selected
at random, should be tested.
The factors of direct and reflected glare should be made the paramount ones for schoolrooms. Brightness and diffusive ability are
closely allied. Globes of the best diffusive ability only should be
considered. A test for diffusive ability is the inability of the observer to locate the position of the light source within the luminaire


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26

CODE OF LIGHTING SCHOOL BUil,DINGS

when the lamp is correctly centered. Under these conditions all
parts of the projected area appear equally bright.
A ·consideration of shadows on the work is closely allied with
brightness and diffusion of the luminaire. There should be no
shadows so dense as to make vision difficult or so sharply defined
as to cause confusion between the edge of the shadow and a drawn
line, as in drafting. Shadows should be soft and luminous, and
where we are concerned with work on a horizontal plane only, as in
study rooms, they should be reduced as much as practicable.
Excessive and objectionable brightness can occur even when the
table of recommended globe diameters for various sized lamps is
adhered to. The light source should be so, centered within a diffusive enclosing globe that no area of the globe is made unduly bright
because of its proximity to the incandescent lamp filament or.
mantle. If this precaution of correctly centering the filament is
overlooked, one of the essential characteristics of a, good diffusing
glass is sacrificed.
·It should be realized that 2 to 10 per cent in the over...all efficiency·
of a luminaire may be gained by using a holder which is white
enameled on the inside. When stress ,is laid upon high efficiency of
units such a, point ca,n not be disregarded.
Electric luminaires ventilated by means of holes in the globe, reflector, bowl, or accessory parts are subject in most cases to greater
depreciation, due to dust, dirt, and insects, than is found with
luminaires in which .there are no ventilating holes. In addition to
the normal collection of dust on exposed surfaces, holes in the luminaire permit dust accumulation due either to air currents through
the luminaire or to "breathing" of the luminaire when it is turned
on and off. That satisfactory cooling of lumin&ires can be effected
by radiation has been proved by many nonventilated luminaires now
in service. Whether or not ventilation holes are used, care must be
exercised in the design to insure against excessive temperatures of
sockets, fixtures, etc.
Rule 2. Avoidance of glare.1

Th~re are five principal causes of glare:
Brign,tnesa of source.-The light source may be too bright; that
is, the candles per square inch of area may be too great. A glance
at the sun proves that an extremely bright light source withm the
field of vision is capable of producing acute discomfort. Light
sources of far lower brightness .than the sun, such as the filament of
an incandescent electric lamp or the incandescent mantle of a gas
lamp, may also cause discomfort, although the annoying effect is
usually not quite so marked.
Total, volume of light.-Experience has shown that a 500-watt
lamP. in a 10-inch opal globe, hung 7 or 8 feet above the floor and a.
similar distance ahead of the observer, will prove quite as glaring
as the exposed filament of a 50-watt incandescent lamp in the same
location. The brightness of the " opal " globe luminaire is only a
few times that of a candle flame, but the quantity of light which
reaches the eye is so great that its effect is worse than that of the
1

Adapted from the Code of Lfgh~ Factories, Mllls, and ()ther Work Places, lllumtEugineerinJ Soclecy.

:Patinr


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CODE OF LIGHTING SCHOOL BUILDINGS

27

bare filament of lower candlepower, although the latter may
have a brightness as high as 3,000 candles per square inch. An unshaded window often causes ~lare, due, of course, to the large volume
of light rather than to the high brightness of the sky.
L()(Jation in the field of view.-A given light source may be located
at too short a distance from the eye, or it may lie too near the center of the field of vision for comfort; that is, within too small an
angle from the ordinary line of sight. For example, the 500-watt
"opal" globe unit discussed in the previous illustrat10n would seldom cause discomfort if placed, say, 80 feet away from the observer, for at this distance the total quantity of light entering the eye
would be only one one-hundredth of that received at 8 feet. Again,
the same light source would probably be found quite unobjectionable at a distance of 8 feet from the eye, provided this distance was
obtained by locating the lamp 4 feet ahead of the observer and 7
feet above the eye level; in this case the lamp would scarcely be
within the ordinary field of view.
.
The natural position of the eye during intervals of rest from any
kind of work is generally in the horizontal direction, and it is desirable that during such periods the pupil should be freed from the
annoyance caused by glare. Glare becomes more objectionable the
more nearly the light source approaches the direct line of sight.
While at work the eye is usually directed either· horizontally or as
an angle below the horizontal. Glaring objects at or below the
horizontal should especially be :prohibited. The best way to remove
light sources out of the direct lme is to locate them well up toward
the ceiling. Local lamps-that is, lamps placed close to the workif used at all, must be particularly well screened.
Oontra8t with backgrou.nd.-The contrast may be too great between the light source and its darker surroundings. It is a common
experience that a lamp viewed against a dark wall is far more
trying to the eyes than when its surroundings appear relatively
light. A light background requires, first, that the surface should
be painted in a color which will reflect a considerable portion of the
light which strikes it, and, second, that the system of illumination
employed should be sucli as to direct light upon the background.
In many cases the ceiling appears almost black under artificial light
simply because no light reaches it. With daylight, on the other
hand, the walls of a room are often so well illuminated that they
appear brighter than the work itself, and this also is a condition
which is not conducive to good vision. In general, a light tone for
ceilings and upper portions of walls and a paint of medium reflecting power for the lower portion of walls will ordinarily be found
most satisfactory under both artificial and natural lighting.
Where strictly local lighting systems are employed-that is, where
individual lamps are supplied for all benches and machines and
no overhead lighting is added-the resulting contrasts in illumination will usually be found so harsh as to be objectionable even though
the lamps themselves are well shielded. The eyes of the pupil
looking up from his brightly lighted machine or bench are not
adapted for vision at low illuminations; hence, if adjacent objects
and aisles are only dimly lighted, he will be compelled either to


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28

CODE OF LIGHTING SCHOOL BUILDINGS

grope about, losing time and risking accident, or to wait until his
eyes have become accommodated to the low illi;imination. Glancing
back at his work, he again loses time while his eyes adjust themselves
to the increased amount of light which reaches them. If long continued, this condition leads to fatigue, as well as to interference with
vision, and to accidents. In other words, where local lamps are employed there should also be a system of overhead lightmg which
will provide a sufficient illumination of all surrounding areas to
avoid such undesirable contrasts.
Tvme of exposu.re.-The time of exposure may be too great; that
is, the eye may be subjected to the strain caused by a light source of
given strength within the field of vision for too long .a time.
When a pupil is seated and his field is fixed for several hours at
a time, light sources of lower brightness and lower candlepower are
required than where the pupil stands at his work and shifts his position and direction of view from time to time. In the first case the
image of the light source is focused on one part of the retina for considerable periods of time and is obviously more likely to cause discomfort and eyestrain than when present for short periods only.
Those who are forced to work all day at desks facing the windows
are particularly likely to suffer from this form of glare. Such conditions should not be tolerated.
Ra;ting light sources from tle glare standpoint.-It is evident
that the first two factors mentioned as causes of glare, namely, excessive brightness and excessive candlepower, concern the light
source itself, the third factor concerns its location in the field of
view, and the fourth and fifth depend upon the conditions of its use.
Measurements of brightness and candlepower have been made
on a number of light sources found in everyday practice, both
natural and artificial, and Grades from I to X have been assigned to
them. ( See Tables V and VI.)
Light sources in Grades I and II may be termed soft or well
diffused; those in Grades VIII, IX, and X are harsh and almost
certain to cause glare.
Grade III is the limiting grade permissible for the lighting of
schoolrooms. Softer grades are recommended. Light sources
other than those included in Table VI will be found in use; however,
from those which are given in the table it is pos.sible to estimate in
what grades others should be placed.
TABLE

V.-01.assiff,cation of light S-Ources from the standpOint of glare

(Grade I Indicates sources of maximum softness. Grade X indicates sources of maximum harshness.]
Candlepower In direction of eye
Maximum visible
brightness
(candles per square Inch)

Less than 20 to 50
20

50to 150 150to 500

500to
2,000

--Grade

2--------------2Less
to 5than
_____________________
520toto20-------------------100 __________________
100 to 1,000 _______________
1,000 and up ______________


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I
II
II
IV
V
VI

Grade

I
II
III
V
VI
VII

Grade

II
III
IV
VI

vu.

VIII

Grade

II
IV
VI
VII
VIII
IX

Grade

III
V
VII
VIII
IX
X

29

CODE OF LIGHTING SCHOOL BUILDINGS
TABLE

VI.-Bpecf;Pc c1,assiff,cation of Ught sources from the standpoint of glare
as derived from Table V

NATURAL LIGHT SOURCES AS SEEN THROUGH WINDOWS OR SKYLIGHTS
Grails

X
V
III

Sun __ - --- -- --- _-- ---- - -- -- --- -- -- -- -- --- -- ---- -- Verysky
bright
sky ___ ------------------------------Dull
__________________
- ___ - - - _- _- _____ - _- ___ - Sun showing on prism glass ______________________ _

IX

INCANDESCENT MANTLE OAS LAMPS
Mantles

consuming-

I

Large single
mantle or cluster

Olusteror
high-pressure
lamp con12-20 suming above
20 cubic feet
cubic
porhour
feet per
hour

- - - - , , - - - -1- - - , - - - - - - 1

Lamp

cubic
feet per
hour

2-6

5--8
cubic
feet per
hour

8-12
cubic
feet per
hour

Grade

Grade

Grade

Grade

Grade

Olear glassware__________ _
IX
VII
VIII
V
VI
D!Jluslng glassware:
6-lnch globes____________
II
III ---------- __________ -------------8-lnch globes..___________
I
II
IV-VI __________ -------------10-inch globes..______________________________ III-V
V-VII -------------I-II-- ------II-VI-~~~
Semi-indirect units___________________________ II-III
II-IV
ill-VI

i:1~~\igr~---------- ____________________ ---

LUMINAIRES EQUIPPED WITH TUNGSTEN FILAMENT LAMPS

LuminBires
Diffusing glass inclosing units: 1
12-inch maximum diameter______________ _
16-lnch mrudmum diameter______________ _

18-inch maximum diameter______________ _
Semi-inclosing units'------------------------

Semi-indirect units•------------------------Indirect-lighting units.. ______________________ _

Watt

IBlilps

75-100
150-200
300
150-200

300

300
75-100
150-200
300
75-100
150-200
300
75-100
150-200

300

Grade

II-ill
III-V
IV-VI
II-V
IV-VI
III-V
III-IV
IV-VI
IV-VII
I-III
II-III
II-IV
I-II
I-II
II

1 Where a range is given, the best grade, that is the lowest, applies to globes that are
evenly luminous, and the poorest to globes which have a decidedly bright spot in the
center.
• Where a range 1B given, the best grade, the lowest, appUes to bowls that are of dense
glass ; that Is, bowls which reflect nearly all ot the light to the celling,

Rule 5. Switching and controlling apparatus.
Switches should be installed at each point of entrance so that
enough lamps of the regular or emergency lighting can be turned on
to enable a person to proceed safely to the next point of control.
In locating switches or control apparatus it is desirable to arrange
them systematically in all rooms, as this simplifies the fin~ of
such apparatus by those responsible for turning on and off the lights.
A satisfactory arrangement of circuits for the outlets indicated on
the plan of Fig. 3 consists of two circuits parallel to the windows,
controlled by separate switches. As natural light fails, the lighting


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CODE OF LIGHTING SCHOOL BUILDINGS

alo~g the side of the room farthest from the windows becomes inadequate first. This arrangement of circuits permits the add-ition of
artificial light to this area without having to resort to the full system
until such time as its use becomes necessary.
Rule 6, Exit and emergency lighting.
Exit lights are often designed to serve only as light signals or
markers, whereas they can be designed to serve as a part of the emergency lighting system. For example, a direct-lighting open-bottom
luminaire made of opal glass, with green or red screen, serves as a
colored signal by transmitted light and provides uncolored light on
the space beneath the luminaire.
·
Rule 7. Inspection and maintenance.
In order to assure satisfactory results from a lighting system it• is
necessary that systematic periodic examina,tions of the equipment be
made. The reflectors and globes should be washed thoroughly at
least once in every two months. In the interim they sfiould be
cleaned by wiping with a damp cloth. During the monthly cleaning
· the condition of the lamps should be noted, and any burned-out or
blackened lamps should be replaced. A sufficient supply of gas
mantles and of lamps of the proper voltage and wattage should be
kept on hand to take care of any contingencies. Any defects in wiring, switches, or other parts of the system should be promptly repaired. Walls and ceilings should be cleaned at given mtervals and
redecorated when necessary. Some responsible person or /ersons
should be assigned the duty of maintaining the equipment an a definite schedule of inspection should be laid out and adhered to. The
foot-candle meter, a device which will indicate illumination intensities at the work place, reveals the combined effect of all possible
causes of depreciation. This instrument used systematically in conjunction with written records affords an excellent means of insuring
the maintenance of illumination intensities provided by the lighting
installation when originally installed. The illumination intensities
in Table I are values which should be maintained; therefore, in
order to anticipate depreciation a surplus of light should be allowed
for in the original design.

Rule 8. Blackboards.
In Fi~. 2 are l'!hown some simple graphical considerations of blackboard lighting. In (a) is shown a plan view of a room with windows on one side. Rays of light are indicated by A, B, and C in
horizontal projection. These are supposed to- come from a bright
sky. By the application of the simple optical law of reflection-the
angle of reflection is equal to the angle of incidence-it is seen that
pupils seated in the shaded area will experience glare from the blackboards on the front wall, if they have a glossy surface. In (b) is
shown the vertical projection of the foregoing condition. It will be
apparent from this graphical illustration that by tiltin~ the blackboard away from the wall at the top edge, the pupils m the back
part of the room will be freed from the present glaring condition.
Whether or not this tilting will remedy bad conditions may be
readily determined in a given case. In (b) the effect of specular re-


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CODE OF LIGHTING SCHOOL BUILDINGS

31

flection of the image of an artificial light source is shown by B. In
( c) i~ shown a proper method of lighting blackboards by means of
local artificial lighting units. This will often remedy bad lighting
conditions whether due to an insufficient illumination intensity of
daylight or to reflected images of bright natural or artificial light
sources.
Experience has shown that black slate is the. most satisfactory material of which to make a blackboard.


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SUBJECT INDEX
Paire

Pap

Daylight lamps _______________
15
Definitions (footnote)_________
2
4, 6 Design of lighting installation_
15
4
3, Desks, illumination on_________
5,6, 11-26 Direct lighting________________ 12, 13
lighting luminaires, diaPhotographs showing poor_ 17, 18 Direct
gram of____________________ 12,13
Photographs showing good19,
4
.
20,21 Drafting rooms, illumination in_
Assembly rooms, illumination in_
4 Drives and roadways, illuminaAuditoriums:
tion on---------------4
Iliumination in ___________ _
4
4 Elevator cars, illumination in__
Illumination of exits of___ _
4 Emergency lighting__________ 5, 7, 30
Entrances, switches at ________ 5, 29
Blackboards :
Eexim, llghting at_ ________ 4, 5, 7, 30
Diagram
of glare received
from ___________________
9
Explanation of technical terms_
2, 3
28
Dullness of --------------5, 8 Exposure, time of_____________
Illumination of___________ !i, 8, 30 Eyesight of children___________
6
Location of_______________ ·5, 8 I!'inish of walls and ceilings____
5, 7
2
Boiler rooms, illumination in___
4 Fire hazard __________________
2
Book shelves, illumination on__
4 Foot-candle, explanation of____
Gas mantle lamps, luminous
Brightness :
Excessive, producing glare_
26
22
flux -----------------------Explanation of___________ _
8 Glare:
Avoidance
of
_____________
4,
6
Units of brightness _______ _
8
Brightness of source_________ _
Causes of________________
26
26
Building code requirements___ _
Classification o f I i g h t
2
sources according to_____ 28, 29
international,
explanaCandle,tion
of ________________
_
25
2 Globes, recommended sizes of__
Catalogues, illumination of___ _
4
4 Gymnasiums, illumination in___
Ceilings, finish of____________ _ 5,7 Illumination:
Charts, illumination on _______ _
Computation
of____________
23,
24
4
Children:
Recommended------------4
Required__________________ 8,6
Eyesight of_______________
5. 6
Indirect
lighting______________
13,
14
Requirements of illumination for __:______________
5, 6 Indirect luminaire, diagram of_
14
Inspection
of lighting installa-5, 7,30
Classrooms :
tions _______________________
Diagram
of illumination_
in _____________________
10 Installations, design of_________
15
Exits from _______________ _
4
5 Laboratories, illumination in___
Illumination in ___________ _
4 Lamps:
Computation of size_______ 23, 24
Coefficients of utilization :
Explanation of____________
3
Gas-filled tungsten, lumens
emitted ________________ _
Table of __________________
22
15
Jolor and finish of interior __ 4, 5, 6, 7
Gas mantle lamps, lumens
emitted
________________
_
Dolor of walls and ceilings _____ 4, 5, 7
22
::lontrast with background _____ 27, 28 Landings, illumination on _____ _
4
Libraries, illumination in_____ _
::lontrolling apparatus, switching
4
and _____________________ 5,7,29,30 Light courts __________________ _
11
Jorridors, illumination in______
4 Light, distribution of artificiaL_
4,6
Jourts, influence of____________
11 Lighting:
Direct
____________________
12,
13
Daylighting:
Emergency________________ 5,7,30
General requirements for__
3,
Indirect___________________ 13,14
5,6,8--11
Semi-indirect______________ 13, 14
Photographs showing poor_
16
Photographs showing good_ 16, 20 Lighting systems ______________ 12-14
33
Aisles, illumination in________ _
Artificial lighting :
Distribution of____________
General requirements for__


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84

CODE OF LIGHTING SCHOOL BUILDINGS
Page.

Pagll

Semi-indirect lighting__________ 13, 14
Semi-indirect
luminaires, dia-_
grams of___________________
13,14
Sewing, illumination on__.____ _
4
Sight of children _____________ _
5,6
Sizes of globes _______________ _
25
Sky
angle
and exposure in 10,11
rooms
______________________
Stairways:
Color of nosing of treads __
5
Illumination on __________ _
4
Storage spaces, illumination in_
4
Study rooms, illumination in __ _
4
Swimming
pools, illumination
on_______________________
_
4
Switching and controlling apparatus __________________ 5, 7, 29, 30
Systems of lighting____________ 12-14
Technical terms, explanation of_
23
Toilets, illumination in________
4
Unilateral lighting____________
8
Volume of light, totaL_________
26
Walks, illumination on________
4
Walls, finish oL_______________
5, 7
Wash rooms, illumination in___
4
Windows:
·
1(
Lighting value of a window
Location of______________ _
~
Window shades______________ _
11
Workshops, illumination in ___ _
4

Location
of lights producing_
glare _______________________
27
Locker spaces, illumination on
4
Lumen, explanation of ________ _
2
Luminaire:
Diagram of____________ 12, 13, 14
Explanation of____________
3
Selection oL______________ 2-!-26
Types of__________________ 12-15
Maintenance• of lighting______ 5, 7, 30
Manu_al t~aining rooms, illumination m __________________ _
4
Minimum illumination required_ 3, 4, 0
Natural lighting:
Photographs showing poor_
16
Photographs showing good_ 16, 20
Requirements for _____ 3,5,0,8-11
Outlets, diagram of____________
10
Output in lumens of gas-filled
tungsten lan1ps _____________ _
15
Playgrounds, illumination on __ _
4
Power plants, illumination in __ _
4
'Rating light sources from the
glare standpoint_ ___________ _
28
Reading tables, illumination on_
4
Recreation rooms, illumination
4
in-------------------------Refiection factor, explanation oL .
3
Requirements, generaL _______ _ 3-5
Rules for lighting____________ _ 3-5
Selecting a luminaire _________ _ 24-26


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0