Improper lighting may be as productive of accidents as inadequate lighting, and throughout the industries and upon the streets the misuse of light is in evidence.  The blinding effect of a brilliant light-source is easily proved by looking at the sun.  After a few moments great discomfort is experienced, and on looking away from this brilliant source the eyes are temporarily blinded by the after-images.  When this happens in a factory as the result of gazing into an unshielded light-source, the workman may be injured by moving machinery, by stumbling over objects, and in many other ways.  Unshaded light-sources are too prevalent in the industries.  Improper lighting is likely to cause deep shadows wherein many dangers may be hidden.  On the street the glare from automobile head-lamps is very prevalent and nearly everybody may testify from experience to the dangers of glare.  Even the glaring locomotive head-lamp has been responsible for many casualties.

Unfortunately, natural lighting outdoors has not been under the control of man and he has accepted it as it is.  The sky is a harmless source of light when viewed outdoors and the sun is in such a position that it is usually easy to avoid looking at it.  It is so intensely glaring that man unconsciously avoids looking directly at it.  These conditions are responsible to an extent for man’s indifference and even ignorance of the rudiments of safe lighting.  When he has artificial light, over which he may exercise control, he either ignores it or owing to the less striking glare he misuses it and his eyesight without realizing it.  A great deal of eye-strain and permanent eye trouble arises from the abuse of the eyes by improper lighting.  For example, near-sightedness is often due to inadequate illumination, which makes it necessary for the eyes to be near the work or the reading-page.  Improper or inadequate lighting especially influences eyes that are immature in growth and in function, and it has been shown that with improvements in lighting the percentage of short-sightedness has decreased in the schools.  Furthermore, it has been shown that where no particular attention has been given to lighting and vision, the percentage of short-sightedness has increased with the grade.  There are twenty million school children in this country whose future eyesight is in the hands of those who have jurisdiction over lighting and vision.  There are more than a hundred million persons in this country whose eyes are daily subjected to improper lighting-conditions, either through their own indifference or through the negligence of others.

Of a certain group of 91,000 purely industrial accidents in the year 1910, Mr. Simpson has stated that 23.8 per cent. were due, directly or indirectly, to the lack of proper illumination.  These may be further divided into two approximately equal groups, one of which comprises the accidents due to inadequate illumination and the other to those toward which improper lighting was a contributing cause.  The seasonal variation of these accidents is given in the following table, both for those due directly or indirectly to inadequate and improper lighting and those due to other causes.