The answer to this is simple if you keep the Venus Fly Trap outside or in an unheated garage or cool windowsill. It should receive however much light it gets from the sun daily. Simple enough, right?
If you have the Venus Fly Trap in a dark basement and you would like to supplement the light it is receiving with artificial lighting, you could give it 10 to 12 hours of light a day. That’s about what it would be receiving if it were outside. On the other hand, if your Venus Fly Trap is in a place where the lights are on for, say, 14 or 16 hours a day, this would be very bad. The plant would think that it is time to come out of dormancy. Be sure not to give a dormant plant more than 12 hours of light a day during dormancy if it is receiving artificial light.