You are correct that bridge circuites require a minimum current for operation. However at null that current flows equally through both legs of the bridge. So unless there is insufficient voltage to pass the minimum current most any power source, in keeping with the basic component, design can be used. That is, too much voltage will certainly burn out something and too little will cause drifting. But in the case of light meters, a couple of tenths of a volt shouldn't matter.Originally Posted by cao
I've used several cells in my Spot and also a Vivitar strap-on (a very miniature meter indeed!), and checked the accuracy with my Minolta Spot meter. No problem.