Ambient temps as Warrior noticed, means everything when deciding what wattage bulb to use. I wouldn't let him get any closer to the lamp than 6 inches. If he is still hanging under the lamp, then he is telling you he wants it warmer. You will need a higher wattage bulb. If this is a young cham, I find it just easier to use a 100 watt lamp hooked up to a rheostat. That way as he gets older you can increase his temps, without constantly swapping out bulbs. The rheostat also allows you to increas the temps with more control.
Still, get a proper digital thermometer before doing anything other than letting him get 2 inches closer. It's very easy to cook him with just the next step up in wattage.
It also sounds as if your cham may be a screen walker. 90% of the time this can be solved by adding more climbing structures for him. You possibly need more cover as well. I find an easy way to add more cover to dowel/bamboo is to buy a large pothos (usually less than 20 bucks at Home Depot) and use the "vines" to wrap around your dowels/bamboo rods.
If after all that he still is a climber, he may want a larger cage, and even then, in the end you may need to take steps to protect his feet. Get some plastic 1/2 inch hardware cloth and line the inside of his cage, to keep his toes off of the screen.
I tested this...be careful. Set it up and test the temps. I use 25w bulbs with branches 6-8 inches away.
