Lights kill humidity?

I have a 20gal long aquarium with one UTH on the warm side, and also a 75w basking lamp. Warm side temps are around 88-91 and cool side temps are around 79-82. I just switched to cypress mulch, but I still am having humidity problems (in the low 40's). Would ditching the lamp for something else help my humidity troubles?

p.s.
I bought the cypress mulch at home depot, and the bag doesn't say anything about being dyed or natural. Is there any way to tell/should I worry?

Hmm... well, first of all yes. Lights do tend to kill humidity, especially ones that high! You really don't need light for a 'warm spot' since these snakes prefer belly heat and spend most of their time "underground" (read in their hides) anyway. If you really want to keep the light, tone it down to at most 50 watts and make sure the lamp is raised at least 8" above the tank lid.

Optimally, you should be getting all your heat from the controlled UTH. How are you controlling it? Rheostats and dimmers are great for temperature controlled rooms or places where the temp only varies one or two degrees... but otherwise you really need a thermostat if you don't have one already.