Leopard gecko questions?

You need the first thermometer (digital probe thermometer).. That's actually the same I have. The warm end should be 90-95 floor temp. If it ends up too cold, that does not mean get a new light bulb. In fact, I would take the one you're currently using out too. Leopard gecko's heat "sensors" are on their belly, so they only can feel heat from the belly. If it's too hot over head, they can't feel that to know to get over to the cool side. They're also nocturnal, so regular bulbs aren't always the best idea during the day. If your temperature is too low, get a new heat mat that will cover 1/3 to 1/2 of the tank floor (if yours doesn't) , and it will be warmer. If you insist on a light, a red heat bulb (no UV or any of that expensive stuff.. And they can't see red.) over the warm hide should be okay, as long as the light isn't directly over the gecko's head.