like lights that light up your tank, ect.
Certain fish prefer shadier tanks than others. As long as you provide adequate hiding places (like with plants/caves/etc) everyone should be happy, but I recommend doing research on whatever kind of fish you have.
If they're meant to be aquarium lights, then you shouldn't have to worry.. it's always nice to have some sort of shade for the fish though, like plants, rocks, etc. They can get startled when you turn the lights on after being in the dark. To prevent this, turn on the room light a few minutes before turning on the aquarium light.
