When I first started my 'bator, I noticed that there was a quick drop/jump in the water wiggler temp when the light was on. I had an epiphany, and this is what solved the problem: I got aluminum foil and some hardware cloth and made a little bulb guard that enclosed the bulb on all sides but the top (out of hardware cloth). Then I got the foil and covered the guard on the front, bottom and right side, leaving the top and left side open to prevent overheating and a fire hazard. This made it so that the eggs were not in direct light, and any heat they got was from the air and not from sitting in the light of a 40watt bulb. Not only did my temps stabilize, but I realized that my thermostat was way too low without the direct light, and ever since my temps have stayed within .5 degree of 99.5, usually closer to .3 of a degree (aside from the usual temp spikes/drops here and there just to give me a heart attack). It also helped stabilize my humidity, and made it MUCH easier to regulate/increase/decrease. Anyways, hope this helps! I'm sure someone else has already come up with this, but just thought I'd post it anyway!!!