Why not just get some blue LEDs that turn on at night for a couple hours after your main lights go out?
If not, messing with lights when you have live plants is not the best thing, unless you want to get more light. Light for an aquarium is rated in WPG (watts per gallons) for T8 lights. I would not go below 1 WPG. More realistically would be 1.5 WPG for a low-tech planted tank. The more light the better, your plants will grow better and faster. If you reduce the amount of light in your tank. your plants will not grow as well as before.
How long have you had your tetras? Odds are you just got them in the last couple weeks and they are still adapting to their new home. Once they are comfortable with their new home they should come out a lot more.
-FHM