You may not get away with just one bulb. Things are always changing. Also when winter comes, you may have to change up.
Your size will probably be different than mine. I don't know what size tank you have.
My tanks are 36" long and run from 12,and 18 wide to 18 and 20 high.
The type of substrate can make a difference because of the amount of water it may be holding, thus humidity levels.
I know this is the long way around the barn, but I would suggest trying a 100 watt bulb. That way you can always use a dimmer and turn it down.
You can get this table top slider dimmer at Lowes for under 10 bucks online or in store.
Tapatalk is down for this forum right now, so I am unable to post a pic of the dimmer. I will add a photo in a different post when able.