I'm sorry fhbob. I seemed to have missed the 100 watt bulb you have already.

A che directs the heat where it is pointed creating a better hot spot. While a bulb will flood heat in the whole tank, unless you are using a basking bulb because they provided directed heat like a che.

A 100 watt over a twenty gallon tank is pretty large. If it is providing a hot spot within the correct range and keeping the ambient temp correct it should be fine. If the hot spot is to hot a better option may be to use a smaller watt bulb on each side of the tank so the heat is more evenly distributed. I think a bulb is best for you and your setup.

Im really sorry I didn't read your post correctly. I'm on a tablet and sometimes scroll to far and miss a line without noticing it.