My incubator is a insulated box. I don't use it often, and usually have only done a dozen eggs at a time, although once my sister borrowed it and had 24 eggs in it.Just 25 watts? How large is your incubator? Mine holds 300 eggs. I keep 2 60 watt bulbs on top and to keep the heat even, I did put the reptile heater bulb in the bottom, a ceramic fixture. There are 2 fans, one top and one bottom to keep it circulated.
So far, so good and not too hot. Seems just right. I'll replace the two on top with the heat bulbs as well but I want to put a metal plate on the ceiling to avoid fire hazards
I have configured it different ways depending on the environmental conditions in the room where I have it set up.
I have a heating pad in the bottom, which was set on low the first few times I used it. I have tried different wattage bulbs, 25 and 40.
When my sister borrowed the incubator, she added an insulated cover, and it it overheated with the heating pad on, so she turned it off and just used the light bulb for heat. I think she used a 40 watt bulb.
FYI, I have been told that incandescent bulbs will still be available for certain appilcations, like appliance bulbs (oven lights) and as HatchCraft wrote above, there will still be "rough service bulbs" available. Here's a link to one source: http://www.arizonatools.com/light-bulbs/detail/ROUGHSERVICEBULB/