Yes, the bleach is in there to prevent algae, fungi and stuff from growing.
Here's an article about ithttp://www.bbc.co.uk/news/magazine-23536914
Using bleach is - in the circumstances - probably the best solution, because most people will have bleach or have easy access to bleach, whereas it might be harder to get something less aggressive. An at least 20% solution of alcohol in water might work, too, but I don't know if it is cheaper. And cheap is what it's supposed to be. Else you could just install a window or use specially designed glass/ plastic cylinders that might yield more light.
I like this idea, although a bulb that only glows during daylight seemed odd at first.