Actually if it's in the 50's the beers might never carb. Low 50's are usually around the temps that yeast go dormant and flocullate, if that's the case, then sleeping yeast aren't going to do the job for you.
You need to raise the temp some how. One way would be to put the beer cases in a sleeping bag and pointing a space heater at them.
If you're going to use a lightbulb, make a paint can heater.
That way except for a couple vent holes on the can somewhere, little light will actually escape. Put that into a box with the bottles.