|Revere camera with large Selenium cell meter.|
Selenium cell meters are easily identified by a faceted or multi-waffled glass plate on the front of the camera or around the lens. Often these meter cells were small, as not a lot of electricity was needed to measure light leverls, but it was not uncommon to see very large use of Selenium in cameras where automatic exposure systems required more voltage (thus more sunlight) to operate.
An upside to Selenium cells is that they did not require batteries to operate. As long as light struck the cells, they could make enough juice to move a meter needle and tell you which f-stop or shutter speed would be best for the light at hand. If you left your camera in its leather case, the meter was effectively shut off.
The downside to this system was that the light-producing ability of Selenium cells eventually ceased over time with exposure to light, particularly bright sunshine. Its ability would be consumed.
Many vintage cameras are found with dead Selenium meters. Sometimes it's because of deteriorating wiring due to poor soldering or a shock to the meter system, which were pretty delicate in those days. But very often, the camera may have been stored in the "on" position with its meter cell exposed to light over years, maybe decades.
Camera collectors like to show-off their possessions on shelving or cabinets. Only natural. But care should be taken to protect examples with Selenium cell meters. Left on a shelf in even a dimly lit room, the light-sensing ability of the Selenium cell is "on".
If you plan on passing on a working model of some old Kodak Retina or Canonette to family or other collectors, you really should turn off the Selenium cell until you either want to use the camera, or want to display it for someone. I've found the simplest method is to use black electrical tape. It's cheap, stylishly black, opaque and easily removed at any time. For less than two bucks you can cut enough light-blocking tape to over hundreds of meter cells.
Hopefully, by covering the meter cell with tape, you'll buy enough time to give the next generation of collector working examples of these 60+ year-old cameras.