Man's physical universe

xanabras

444 ENERGY MAY BE PROPAGATED BY VIBRATIONS

10-15 foot-candles — stores and general factory work.

10-20 foot-candles — offices and classrooms, general

reading, writing, and sewing.

20-30 foot-candles — typing and average office-work.

20-50 foot-candles — drafting and fine office-work,

prolonged reading, especially

of fine print, fine needle-work.

50-100 foot-candles — fine manufacture and inspection.

Your local power and light company will undoubtedly be glad to

render you the service of measuring the intensity of illumination at

various points in your home, office, or shop. This service may be combined

with an attempt to sell you lighting equipment, and it is quite

probable that the service man can give you expert advice concerning

the types of equipment available.

In general, however, once the diagnosis has been made, one should

not take the first cure offered. There may be other equally effective,

more pleasant, and even less expensive, cures available.

In building a new home, the architect is sometimes competent to

work out the illumination problems, but it is often desirable to obtain

the help of an illumination engineer.

Illumination is a technical matter

that requires the aid of a specialist just as sickness requires the aid of a

physician.

Glare and Shadows Should Be Avoided in Illumination.

In designing a lighting system, whether for home, office, or factory,

one should try to avoid glare and shadows which cause eyestrain.

In general, one should keep in mind that it is not the light source that

one wants to see but rather the book, merchandise, or machine, as the

case may be.

Floor lamps and table lamps are good as decorations,

but they are poor for general illumination because they represent light

sources which are in the direct line of vision.

Flush-type ceiling lights,

cove-lighting, concealed floodlighting, and similar types of lighting

represent good lighting practice because the luminaires (luminaire

refers to a light unit which includes lamp fixture, shade or globe)

are kept out of sight, while the light is directed everywhere.

Shadows and all sharp contrasts in illumination should be avoided

because it takes some time for the eye to become adjusted to any given

light intensity. A camera which has been adjusted to take a picture

in the bright sunlight has to have its diaphragm opened to allow more

light to get in for exposure on a cloudy day. When one shifts his eye

from a brightly illuminated book to an object in a poorly illuminated

dark corner, it strains his eyes to see anything. Everyone knows that

it takes time to adjust one's eyes to see outdoors at night when one

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