A Light-time Integrator

A simple and compact electronic circuit, employing a vacuum photocell as the light-sensitive element, is described. By the use of this circuit, and provided that the energy distribution of the source remains invariant, the amounts of radiant energy emitted by a given light source over differing periods of time may be directly compared, provided that the energy distribution of the source remains invariant. If required, and, of course, provided that the photocell employed is sensitive to the radiation, the instrument may be calibrated to measure in absolute units the total monochromatic radiant energy falling on the receiver in any given period of time. It is suggested that the circuit may prove useful for monitoring light sources in photochemical work.