A very long time ago, I read about this and experimented in a dark toilet after sunset. I did get the flash, but it wasn't terribly easy to get a flash with th

A very long time ago, I read about this and experimented in a dark toilet after sunset. I did get the flash, but it wasn't terribly easy to get a flash with the small sugar crystals available to me at the time. The next day, there were ants after all that sugar on the toilet floor (also featured in Feynman's book), leading to further experiments ferrying ants :)