Toronto. When it burst on the scene in the early 1960s, the Gossen Lunasix (Luna-Pro over here) solved the problem of low light readings. Using the recently released Cadmium Sulphide (CdS) photo cell, the meter was both accurate and sensitive. Unlike its predecessor, the Selenium Photo Cell, the CdS cell did not generate an EMF (act like a battery when illuminated). Instead the cell varied its resistance as the light varied.
Gossen made a pricy meter (About $65 when I bought one) but still used a very primitive circuit. Two mercury cells were placed in series with a meter and a resistance. A switch flipped a scale and another resistor in or out to create a two scale instrument for high and low light use. A built-in translucent dome could be moved over the CdS cell to make it an incident light meter. The meter was still a big handful compared to the dainty but sturdy Weston meters. Continue reading

















