If you don't want to do lights on/off in the cages either for cost of the lights or electricity, you could always get a good room lamp that puts off pretty good amount of ambient light for the cages and have that on a timer for all the cages. Just place it where the light will get into the fronts of the cages.
I do this method in my QT room since it has poor lighting and QT snakes are kept in temporary tubs that I can't install lighting inside. My PVC cages run with lighting inside on timers.
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