For this hack, I use "DIY littleBits
" to demonstrate how to override a simple toy switch with alternate switches and a light/dark sensor. It's a great way to startle someone for fun when they turn out the lights at night and a good way to provide an "assistive technology" switch for someone who is lacking fine motor skills.
To learn how to make the power and light trigger circuits, visit https://www.instructables.com/id/DIY-littleBits-Introduction/ ... In that instructable, step 1 is "power" and step 9 is "light trigger". Also visit littleBits.cc
for the open hardware circuit designs.