Very low current (<10 microamps) darkness detector circuit that turns off in light
At 10 microamps, you could just add a solar cell and a (very) low leakage diode. Any reasonable amount of light would then power your circuit instead of the battery.







simulate this circuit &ndash; Schematic created using CircuitLab

The very small current back into the battery can safely be ignored, and the bas116 has nA range leakage current.