Edit:
I checked the Electronic Bricks Cookbook jpd referenced above (rather poor in general) and the code example is really frustrating. Since analogRead() returns an integer, why is it compared to a HEX (0x200) ?? And anyway, if it is HEX it would be 512 decimal; the 2.2 V I mentioned above are even less than that (around 400), given the 10-bit built-in ADC of the AVR chips on Arduinos. If it is meant to be 200 dec, then it is a rather low level to turn the lights on…! 
Anybody, please??