AN INEXPENSIVE INTEGRATING LIGHT RECORDER

Abstract

The construction and operation of the apparatus is described for use on 110-V, 60-cycle current. In operation, light striking the light-sensitive element in a vacuum phototube causes a current to flow which is very closely proportional to the intensity of the light. This current charges a condenser which, when it reaches a critical potential, discharges through a cold cathode gas discharge relay tube. This, in turn, discharges a 2d condenser which operates a sensitive counter. Thus, by calibration, the av. intensity or integrated light during any time interval can be measured. Unless used with monochromatic light or light of constant quality, the results are available only in arbitrary units, such as foot-candle-hrs. Light intensities below 1 ft.-candle have been measured. The low cost (less than $25) of the apparatus, its simplicity of operation, and its probable long life enhances its usefulness for measuring light in the various biol. fields. Examples of the variation in sunlight are given for State College, Pa.