If you cover a light with something (why I have it in a paint can), then you don't have the light issue. I had really short bulb life using foil. Here is a step by step: Fermentation Can Heater
. My only change is that I am using an oven light bulb at 40W and it keeps up with outside temps here (low around 20). Oh, and I didn't route the power cord through the side of the can, I have the 2 wires going in through the lid and ground wired to the lid.
I have used the water bath with heater/pump before and it works really well. It does raise the humidity significantly and I have noticed mold in the fridge pathways. I still use this method for Saison, when I want the temperature up around 90.