Abstract
The photosensitive properties of certain types of neon indicator tubes in relaxation oscillator circuits have been investigated and used in a frequency light meter. Illumination is measured in terms of change of frequency caused by the alteration in the striking potential on irradiation. The experimental results are in accord with the theory and illuminations range from 50 to 104 f.c. Sample calibration curves at low and high levels of illumination are given for a number of tubes.