cooler water slows down their metabolism and makes them a bit sluggish. if you decide to raise it, do it very, very gradually... and be aware that it may mean that everyone eats a tiny bit more.
i have fairly bright lights in my tank (for live plants) and it doesn't seem to bother anyone... they do spaz a little if it suddenly goes either dark or light... so at night for example, i leave the room lights on brightly, and turn off the tank light, and a little while later turn off the room lights, and basically do the opposite in the morning.
couldn't hurt to double check your water parameters too - neons are pretty sensitive to
ammonia/nitrites/nitrates.