IT’S DONE WITH MIRRORS

CD 1964080 E&MP27.045

Electric Lighting

FEB 22 1941

Far removed from the usual inference of that expression is this scientifically exact test of a street lighting unit in a photometric room of the General Electric Illuminating Laboratory at Schenectady, N.Y. One of a number of intricate tests to determine whether electric lamp units can take it under all kinds of weather and operating conditions, this is a light distribution test.

The mirror at the upper right reflects light from the unit back to a photo cell at the other end of the room where a reading is taken. Movement of the mirror gives light readings in the vertical plane, while rotation of the lamp unit itself affords light readings in the horizontal plane. The circular shield in front of the unit prevents direct light from reaching the photo cell. 

Original Caption by Science Service
^©General Electric