Is there any reason that you need a lamp? If you don't need one, don't use one. It is more trouble than it is worth. Trust me.
If you live in a dry climate you will be constantly fighting with that lamp to maintain humidity.
I used to use a lamp with a 60 watt red bulb and I had it directly over a large waterbowl. I had most of the top of the cage covered and I still had to mist in the morning and in the evening. I have recently switched to a UTH and now the humidity is perfect on its own and I have never had to mist once since I changed over.
UTHs are a beautiful thing.