The Birmingham age-herald., 1911-04-30
HE EYE OF
 THE MOTOR GAR Importance of Sufficient Power in Headlight
COSTLY CARELESSNESS
Three Principal Points to Be Consid- cred by Owners-Best Method of Lighting the
 Roadway
From Harner,s Weekly.

Few motoring experiences are more unpleasant than driving car equipped with defective headlights along a strange road on dark night. The imperfect illumination seems to define rather than to penetrate the sur rounding blackness. and there is never absent from the motorists mind the feeling that some unknown obstacle may lie hidden in the obscurity ahead Of him. While the actual danger in such a case may not be very great, it Is real, and, seeing that a motor car is too valuable a piece of property to be exposed to unnecessary risks, the motorist, if he is well advised, will not begrudge a little attention devoted to his lamps to insure that optically they should be.
 Because it has no complicated parts and calls for little care or manipula- tion, the common tendency is to take the lamp for granted and to regard the lighting problem as a generation problem exclusively. This Is doubly a mistake In the first place. whether electricity or gas be the preferred il- luminant, the most efficient generating equipment will fail of it's purpose if the construction of the lamp which it feeds be faulty. Tn the second place. badly designed lamps are commoner than is generally supposed, and many a car owner is under the impression that his lamps are not large enough when the real trouble is that they are inefficient
 The three principal points which must be considered in connection with lamp efficiency are: CD The brilliancy or illumina ting power of the flame or hlament, % the consumption of gas or electricity; (3) the suita bility of the optical devices employed to throw the light where it can do most good. We shall consider these in the order named and then pass on to one or two other points which are worth looking to, al- though their importance is by com parison secondary.
 All physical quantities are for the pur- poses of comparison estimated by means of a unit quantity of their own kind Thus an area is measured in terms of some standard area such as a square foot, and in the same way the intensity of a source of illumination Is measured by the intensity of the light from a standard can dle made of either sperm or paraffine and weighing one-siXth of a pound. For in stance, the intrinsic brilliancy of the sun is equal to 500,000 candles per square inch. that of an incandescent carbon fila ment to between 150 and 200 candles and and 100 candles per square inch of surface in each case also.
 The candle power of the unre1ected flame or flament of a headlight should not be less than 15 nor greater than 20. With acetylene as the illuminant this will call for the delivery at most of ' cubic feet of gas per lamp per hour. Where gas tank is used charge of 100 cubic feet should thus be sufficient to maintain two headlights in operation for about 70 hours. The corresponding con- sumption of carbide, where the acetylene is generated on the car, would be about 25 pounds for the same period and ser vice. If in ethet case the actual figures are in excess of these, the light is un- necessarily brilliant or the burner is dirty or defective, or the gas is being delivered at too great a pressure. If the lighting equipment is electrical and tungsten or tantalum bulbs are employed the con sumption of electrical energy should not exceed 25 watts per lamp. The older the filament the greater the cost, electrically, per candle power per hour
 Since a flame projects its rays impar- tially in ali directions the amount of it.
 
 we imagine 8 source of light to be placed at the center of sphere of one foot radius. the surface of that sphere will in- tercept all the rays and each point on it will receive definite amount of illumina- tion. Now suppose the radius of the sphere to be doubled Its surface will be increased fourfold, and, therefore, each point on it will only receive a quarter of the light it did before. If the radius be trebled the illumination at a point on the sphere will be a ninth, and so on, the amount of light intercepted by a given area diminishing as the square of it's distance from the center of illumination. The degree of illumination produced by standard candle at a distance of one foot is known as a candle foot.
 The purpose of the lenses and reflectors with which lamp is fitted is to defect the divergent rays from the flames or fi'ament and concentrate them in paral- Tel beam. If the source of illumination were mathematical point, it would be