Electricity gives the very best light, with a minimum amount of heat and vitiation of the atmosphere. For individual use 16-candle power is sufficient.
The lamp-shade should be opaque, of a dark-green color, and lined with a white, reflecting surface. Transparent lamp-shades, especially when patterned, are always bad, whatever their color; because of the different degree of illumination thrown upon the work, the light is irritating to the eyes.
Hygienic Precautions in Reading and Sewing.—There should be free access of open daylight. Near the window is obviously the best place for working, and the seat should be so selected that the window is to the left of the worker. This prevents the work from being shaded by the hand, and protects the eyes from being fatigued by the light falling directly into them.
Any room will have too much light into which the sun shines directly. Even if the worker’s face is not turned directly toward the sun, yet the light reflected from the book or other work will be so intense as to be dazzling. The softest and most pleasant light to work by is the diffused light from the northern sky. An excess of light may be easily regulated by a shade.
Reading.—Very fine type should always be avoided, it is a very unnecessary strain on the eyes, as are also books printed on a poor quality of paper with improper spacing. The paper should be unglazed.
Length of Line.—The length of the printed line should not be more than 4 inches, nor less than 2¾ inches; that is, not more than 10 or less than 7 centimeters. If the line is too long, the effort to find the succeeding line is too great. If, on the other hand, the line is too short, the lateral movements of the eye are so frequent that the muscles concerned in these movements soon become fatigued.
The position of the reader should be sitting upright, with the back toward the light, which should fall over the left shoulder, and the book held nearly on a level with the eyes. The book should be held at a distance of about 12 inches from the eyes. The light should be on a level with the head or slightly above it. In desk work, a shade should always be worn to protect the eyes.
Reading in the recumbent position is a pernicious habit, and is particularly bad when convalescing from an illness or when very tired.
Reading in carriages or cars is injurious to all eyes, but especially so to myopic eyes; because of the constant jolting, the distance between the type and the eyes is continually changing, necessitating the frequent and abrupt adjustments of accommodation; besides, the illumination is apt to be very poor. Reading in a dim light or the twilight is also very bad for the eyes.
Sewing and embroidery require the most trying ocular labor and the best conditions for illumination. Working on black goods by artificial light should be absolutely forbidden.