yup,like Pat said
insulation on the outside
if you have the realy old x-mas lights(showing my age here)from like the 40's-70's
the ones with the realy large tapered bulbs,like and inch and a half long and near as wide(like the ones in the movie A CHRISTMAS STORY)
they would probably work as they would start dry trees on fire
thats why they went to the smaller bulbs,and now the LED bulbs
but there are much better choices
a regular socket and 100 watt bulb would work much better,especially if you put one on each end of the pipe