Under this name, Radioelectronics magazine published in the January 1974 issue a light exposure meter for photographers. The circuit used general-purpose transistors and a FET, with an LDR sensor.
This radio version with a transistor for a crystal phone was found in a Japanese magazine from...
In this circuit of Texas Instruments an incandescent lamp is used as a light source, and lenses are...
This source whose voltage depends only on the zener diode used, can supply currents up to about 3 A....