Abstract :
A number of states, particularly the more densely populated ones having complicated traffic problems, have automobile headlight legislation which specifies maximum and minimum candle power values at various angles, in order to eliminate objectionable glare and provide adequate road illumination. The ordinary photometric equipment available for making tests of this kind in the laboratory is usually very cumbersome and expensive. At the same time, many of the companies manufacturing and handling headlighting equipment have use for a portable and inexpensive photometric instrument enabling them to make fairly accurate candle power measurements under factory or service conditions. A number of devices is being marketed, suitable for this purpose. Of these the simplest and least expensive is the foot-candle meter. As commonly employed for industrial and similar commercial purposes it is graduated for illumination values somewhat higher than the minimum values ordinarily measured with automobile headlighting equipment. The regular foot-candle meter may, however, be simply and easily adapted to this special work by the addition of a 1/100 point on the voltmeter scale as shown in Fig. 1, thereby permitting of readings as low as 100 candle power at 100 feet ahead of the car.
