No expert, but I know with my 10 gallon it wasn't the light per se, just that I left it on 24 hours a day when I didn't know any better. If you keep the lights on for 10 hours a day or so, and reliable leave them off the rest of the time, they'll get used to the cycle. This is assuming your tank isn't in the sunlight, which it shouldn't be anyway, especially with a tank that small. Better yet, use a timer. You can get 'em cheap at any home despot, blowes, or mall-wart.
Also, are you using wee incandescents? What sort of wattage are we talking about?