It is established that outdoors life and property are at night safer under adequate lighting than they are under inadequate lighting. Police departments in the large cities will testify that street-lighting is a powerful ally and that crime is fostered by darkness. But in reckoning the cost of street-lighting to-day how many take into account the value of safety to life and property and the saving occasioned by the reduction in the police-force necessary to patrol the cities and towns? Owing to the necessity of darkening the streets in order to reduce the hazards of air-raids, London experienced a great increase in accidents on the streets, which demonstrated the practical value of street-lighting from the standpoint of accident prevention.

During the war, when dastardly traitors and agents of the enemy were striking at industry, the value of lighting was further recognized by the industries, with the result that flood-lighting was installed to protect them. By common consent this new phase was termed "protective lighting." Soon after the entrance of this country into the recent war, the U.S. Military Intelligence established a Section of Plant Protection which had thirty-three district offices during the war and gave attention to thirty-five thousand industrial plants engaged in production of war materials. Protective lighting was early recognized by this section as a very potential agency for defense, and extensive use was made of it. For example, Edmund Leigh, chief of the section, in discussing the value of outdoor lighting stated:

An illustration of our work in this connection is the case of an $80,000,000 powder plant of recent construction. We arranged to have all wires buried. In addition to the ordinary lighting on an adjacent hill there is a large searchlight which will command any part of the buildings and grounds. Every three hundred yards there is a watch-tower with a searchlight on top. These searchlights are for use only in emergency. Each tower has a telephone service, one connected with the other. The men in the towers have a view of the building exteriors, which are all well lighted, and the men in the buildings look across the yard to the lighted fence line and so get a silhouette of persons or objects in between. The most vital parts of the buildings are surrounded by three fences. In the near-by woods the underbrush has been cleared out and destroyed. The trunks and limbs of trees have been whitewashed. No one can walk among these trees or between the trees and the plant without being seen in silhouette.... I say flatly that I know nothing that is so potential for good defense as good illumination and at the same time so little understood.

Without such protective lighting an army of men would have been required to insure the safety of this one vital plant; still it is obvious that the cost of the protective lighting was an insignificant part of the value of the plant which it insured against damage and destruction.The United States participated for nineteen months in the recent war and during that time about 400,000 casualties were suffered by its forces. This was at the rate of about 250,000 per year, which included casualties in battle, at sea, and from sickness, wounds, and accidents. Every one has felt the magnitude of this rate of casualties because either his home or that of a friend was blighted by one or more of these tragedies in the nineteen months. However, R.E. Simpson of the Travelers Insurance Company has stated that:

During a one-year period in this country the number of accidents due to inadequate or improper lighting exceeds the yearly rate of our war casualties.

This is a startling comparison, which emphasizes a phase of lighting that has long been recognized by experts but has been generally ignored by the industries and by the public. The condition doubtless is due largely to a lag in the proper utilization of artificial lighting behind the rapid increase in congestion in the industries and in public places.

Accident prevention is an important phase of modern life which must receive more attention. From published statistics and conservative estimates it has been concluded that there are approximately 25,000 persons killed or permanently disabled, 500,000 seriously injured, and 1,000,000 slightly injured each year in this country. Translating these figures by means of the accident severity rates, Mr. Simpson has found that there is a total of 180,000,000 days of time lost per year. This is equivalent to the loss of services of 600,000 men for a full year of 300 work-days. This loss is distributed over the entire country and consequently its magnitude is not demonstrated excepting by statistics. Of course, the causes of the accidents are numerous, but, among the means of prevention, proper lighting is important.

According to some authorities at least 18 per cent. of these accidents are due to defects in lighting. On this basis the services of 108,000 men as producers and wage-earners are continually lost at the present time because the lighting is not sufficient or proper for the safety of workers. If the full year's labor of 108,000 men could be applied to the mining of coal, 130,000,000 million tons of coal would be added to the yearly output; and only 10,000 tons would be necessary to supply adequate lighting for this army of men working for a full year for ten hours each day.

Statistics obtained under the British workmen's compensation system show that 25 per cent. of the accidents were caused by inadequate lighting of industrial plants.

Much has been said and actually done regarding the saving of fuel by curtailing lighting, but the saving may easily be converted into a great loss. For example, a 25-watt electric lamp may be operated ten hours a day for a whole year at the expense of one eighth of a ton of coal. Suppose this lamp to be over a stairway or at any vital point and that by extinguishing it there occurs a single accident which involves the loss of only one day's work on the part of the worker. If this one day's time could have produced coal, there would have been enough coal mined in the ten hours to operate the lamp for thirty-two years. The insignificant cost of lighting is also shown by the distribution of the consumption of fuel for heating, cooking, and lighting in the home. Of the total amount of fuel consumed in the home for these purposes, 87 per cent. is for heating, 11 per cent. for cooking and 2 per cent. for lighting. The amount of coal used for lighting purposes in general is about 2.5 per cent. of the total consumption of coal, so it is seen that the curtailment of lighting at best cannot save much fuel; and it may actually result in a great economic loss. By replacing inefficient lamps and accessories with efficient lighting-equipment and by washing windows and artificial lighting devices, a real saving can be realized.

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.

Seasonal Distribution of Industrial Accidents Due to Lighting Conditions and to Other Causes

The figures in one column have no direct relation to those in the other; that is, each column must be considered by itself. It is seen from the foregoing that about half the number of the accidents due to poor illumination occurred in the months of November, December, January, and February. These are the months of inadequate illumination unless artificial lighting has been given special attention. The same general type of seasonal distribution of accidents due to other causes is seen to exist but not so prominently. The greatest monthly rate of accidents during the winter season is nearly four times the minimum monthly rate during the summer for those accidents due to lighting conditions. This ratio reduces to about twice in the case of accidents due to other causes. Looking at the data from another angle, it may be considered that the likelihood of an accident being caused by lighting conditions is about twice as great in any of the four "winter" months as in any of the remaining eight months. Doubtless, this may be explained largely upon the basis of morale. The winter months are more dreary than those of summer and the workman's general outlook is different in winter than in summer. In the former season he goes back and forth to work in the dark, or at best, in the cold twilight. He is not only more depressed but he is clumsier in his heavier clothing. If the enervating influence of these factors is combined with a greater clumsiness due to cold and perhaps to colds, it is not difficult to account for this type of seasonal distribution of accidents. A study of the accidents of 1917 indicated that 13 per cent. occurred between 5 and 6 P.M. when artificial lighting is generally in use to help out the failing daylight. Only 7.3 per cent. occurred between 12 M. and 1 P.M.

There is another aspect of the subject which deals particularly with the safety of the light-source or method of lighting. As each innovation in lighting appeared during the past century there immediately arose the question of safety. The fire-hazard of open flames received attention in early days, and when gas-lighting appeared it was condemned as a poison and an explosive. Mineral-oil lamps introduced the danger of explosions of the vapors produced by evaporation. When electric lighting appeared it was investigated thoroughly. The result of all this has been an effort to make lamps and methods safe. Insurance companies have the relative safety of these systems established to their satisfaction and to-day little fire-hazard is attached to the present modes of general lighting if proper precautions have been taken.

When electric lighting was first introduced the public looked upon electricity as dangerous and naturally many questions pertaining to hazards arose. The distribution of electricity has been so highly perfected that little is heard of the hazards which were so magnified in the early years. Data gathered between 1884 and 1889 showed that about 13,000 fires took place in a certain district. Of these, 42 were attributed to electric wires; 22 times as many to breakage and explosion of kerosene lamps; and ten times as many through carelessness with matches. These figures cannot be taken at their face value because of the absence of data showing the relative amount of electric and kerosene lighting; nevertheless they are interesting because they represent the early period.

There are industries where unusual care must be exercised in regard to the lighting. In certain chemical industries no lamps are used excepting the incandescent lamp and this is enclosed in an air-tight glass globe. Even a public-service gas company cautions its employees and patrons thus: "Do not look for a gas-leak with a naked light! Use electric light." The coal-mine offers an interesting example of the precautions necessary because the same type of problems are found in it as in industries in general, with the additional difficulties attending the presence or possible presence of explosive gas. The surroundings in a coal-mine reflect a small percentage of the light, so that much light is wasted unless the walls are whitewashed. This is a practical method for increasing safety in coal-mines. However, the most dangerous feature is the light-source itself. According to the Bureau of Mines during the years 1916 and 1917 about 60 per cent. of the fatalities due to gas and coal-dust explosions were directly traceable to the use of defective safety lamps and to open flames.

In the early days of coal-mining it was found that the flame of a candle occasionally caused explosions in the mines. It was also found that sparks of flint and steel would not readily ignite the gas or coal-dust and this primitive device was used as a light-source. Of course, statistics are unavailable concerning the casualties in coal-mines throughout the past centuries, but with the accidents not uncommon in this scientific age, with its elaborate organizations striving to stamp out such casualties, there is good reason to believe that previous to a century or two ago the risks of coal-mining must have been great. Open flames have been widely used in this industry, but there has always been the risk of the presence or the appearance of gas or explosive dust.

The early open-flame lamps not only were sources of danger but their feeble varying intensity caused serious damage to the eyesight of miners. This factor is always present in inadequate and improper lighting, but its influence is noticeable in coal-mining in the nervous disease affecting the eyes which is known as nystagmus. The symptoms of the disease are inability to see at night and the dazzling effect of ordinary lamps. Finally objects appear to the sufferer to dance about and his vision is generally very much disturbed.

The oil-lamps used in coal-mining have a luminous intensity equivalent to about one to four candles, but owing to the atmospheric conditions in the mines a flame does not burn as brightly as in the fresh air. The possibility of explosion due to the open flame was eliminated by surrounding it with a metal gauze. Davy was the inventor of this device and his safety lamp introduced about a hundred years ago has been a boon to the coal-miner. Various improvements have been devised, but Davy's lamp contained the essentials of a safety device. The flame is surrounded by a cylinder of metal gauze which by forming a much cooler boundary prevents the mine-gas from becoming heated locally by the lamp flame to a sufficient temperature to ignite and consequently to explode. This device not only keeps the flame from igniting the gas but it also serves as an indicator of the amount of gas present, by the variation in the size and appearance of the tip of the flame. However, the gauze reduces the luminous output, and as it accumulates soot and dust the light is greatly diminished. One of these lamps is about as luminous as a candle, initially, but its intensity is often reduced by accumulations upon the gauze to only one fifth of the initial value.

The acetylene lamp is the best open-flame light-source available to the miner, for several reasons. It is of a higher candle-power than the others and as it is a burning gas, there is not the danger of flying sparks as in the case of burning wicks. The greater intensity of illumination affords a greater safety to the miner by enabling him to detect loose rock which may be ready to fall upon him. However, this lamp may be a source of danger, owing to the fact that it will burn more brilliantly in a vitiated atmosphere than other flame-lamps. Another disadvantage is the possibility of calcium carbide accidentally spilt coming in contact with water and thereby causing the generation of acetylene gas. If this is produced in the mine in sufficient quantities it is a danger which may not be suspected. If ignited it will explode and may also cause severe burns.

The electric lamp, being an enclosed light-source capable of being subdivided and fed by a small portable battery, early gave promise of solving the problem of a safe mine-lamp of adequate candle-power. Much ingenuity has been applied to the development of a portable electric safety mine-lamp, and several such lamps are now approved by the Bureau of Mines. Two general types are being manufactured, the cap outfit and the hand outfit. They consist essentially of a lamp in a reflector whose aperture is closed with a sheet or a lens of clear glass. The battery may be of the "dry" or "storage" type and in the case of the cap outfit the battery is carried on the back. The specifications for these lamps demand that a luminous intensity averaging at least 0.4 candle be maintained throughout twelve consecutive hours of operation. At no time during this period shall the output of light fall below 1.25 lumens for a cap-lamp and below 3 lumens for a hand-lamp. Inasmuch as these are equipped with reflectors, the specifications insist that a circle of light at least seven feet in diameter shall be cast on a wall twenty inches away. It appears that a portable lamp is an economic necessity in the coal-mines, on account of the expense, inconvenience, and possible dangers introduced by distribution systems such as are used in most places.

Although the major defects in lighting are due to absence of light in dangerous places, to glare, and to other factors of improper lighting, there are many minor details which may contribute to safety. For example, low lamps are useful in making steps in theaters and in other places, in drawing attention to entrances of elevators, in lighting the aisles of Pullman cars, under hand-rails on stairways, and in many other vital places. A study of accidents indicates that simple expedients are effective preventives.