88-91 are on a extreme side, you dont want to cook the frog

blue light is visible to a frog, but you don't need to heat your tank if you say you have it at 82-85 without anything.
Yes he needs some light, but dim light is ok, if you feel his ambient room light is not enough you can use regular energy saving lamp( i use 13w) it doesnt add any heat.

Large swings in temps are dangerous.