Temperature Controlling my Fridge

So I've been working on a temperature controlled refrigerator. I'm brewing a Belgian pale tomorrow, and I'm wanting to keep the temperature to 70°.

Trouble is, it's been so cool out that the fridge never warms up enough. Base temp in the fridge is 66° (same as the house).

I read on a different post that someone suggested putting a 100 watt lightbulb inside, and cover it with a tin can. The theory being that it raises the temp inside the fridge, and then the thermostat reads this temperature and turns the fridge on, thus lowering the temp to the target of 70°.

So I installed said lightbulb, and was delighted to hear the fridge turn on. But when I opened the door, I was met with this crazy blast of hot air. I keep a thermometer inside the fridge to double check the temps, and it read 80°!!

So my question is this: my temperature controller has a thermostat placed inside a jar of water, thus implying that the temperature of the water is correct. Is this true? Or would the 80° air temperature be much too warm for the fridge to cool properly?

Should I lower the wattage perhaps?

Other suggestions?

Why keep the probe in a separate jar of water? You'd be much better off taping it to the side of your carboy with a bit of insulation. In any case, the the air in your fridge will certainly exhibit wider swings than your wort temperature will. That said, 100W might be a bit high.