As green is said to be the color of hope, those two oldies should now have lots of it.
They came to me with the classic light bulb, one missing the photo resistor, and both featuring a nice 115VAC transformer and a power cord good for an average home.
The task was to identify a suitable photo resistor (bad, bad CdS stuff that the EU does not want us to use anymore. Maybe they think all the cadmium is urgently needed for cheap chinese power tools that find an early end in the dustbin due to their quality anyway?), remove the circuitry and design a driver circuit for a LED – a green one, matching with the sensitivity maximum of the photo resistor. A switch mode converter was used to allow the longest possible operation from 9 volts battery. For this purpose, a battery compartment has been mounted into the base plate. As soon as the battery voltage drops below 7.5 volts, the red indicator LED on the front starts flashing slowly.
Here’s the new circuitry: