The faster the Thermostat cycles the more steady a temperature you will have. Use a heavy duty bulb like those used for an appliance (oven) and it will survive longer. backup is a very good plan. My current set up (soon to change again) is a separate box with 3 90 watt bulbs in it. the heat is then fan forced tot he incubator where the thermostat is. I have to pay more attention that there are no leaks in the incubator with this set up but it works pretty well. I do get fairly large (5 degree)temp swings though even with a Thermostat that has the face drilled out of it (let's the air get to the metal disk inside). I am going to redo it and place the stat back near the bulbs and add to computer fans to the incubator itself to even out temps throughout. I think the battery in my digital thermometer is low because when I checked the temp this morning it was showing 107 after several days of being between 97 and 101.2. All my liquid thermometers where reading more like 96 to 100 depending on where they where in the incubator. I have parts on order for a completely different type of heat source that may possibly be able to go directly under the eggs. at this time but experimenting with different set ups and seeing which one are easy to put together, which ones are more reliable etc. how well they stabilize and what it takes to get them dialed in to that elusive 99.5 degrees. I will say that the thermostat above your light as you have it is the best i have found for getting stable temperatures and you see it a lot in other home made incubators. This is only in regard to the Water Heater thermostat though. I have yet to test other thermostats but I am waiting for parts to make an electronic thermostat that hopefully will be far more accurate (one half a degree or less) even though it is placed near the eggs which is really where we are worried about temperatures anyway. I also have an idea for little egg cups that are little egg warmers. so each egg has it's own little heater. I will have to see about that one though.
