Cheap photo-optics, light sensors and solar cells.

This is not an advertisement…I was at a few ‘big box’ stores and saw that they had “Solar powered yard lights” on sale. It’s winter and they needed the space for Christmas merchandise. One already inexpensive set was marked down by 50%. 12 solar lights for $9. Yep, 12 solar cells, 12 Cadmium Sulfide Diodes (CDS), 24 Nickel Cadmium AA cells, for $9. Be careful when disassembling the units, as the solar cells are as you know, brittle. Have fun.