Recording Horizontal Atmospheric Transmission of Light at Night

Abstract

A photoelectric telephotometer, which measured the illumination produced at a fixed distance from a light source of known candle power, was developed to record directly the total horizontal atmospheric transmission of light at night over a two sea-mile path. The apparatus consisted of a multiplier phototube, a DC amplifier, batteries for operation, and a one-milliampere recorder. It can be set up easily for field use. A 1000-watt projection-type lamp was used as a light source. By means of a standard lamp, the photoelectric telephotometer was calibrated in a laboratory light tunnel to record illumination in sea-mile candles. In the field the photoelectric telephotometer was compared with a visual telephotometer. Transmission measurements showed good agreement between the photoelectric and the visual methods.