The bulbs need to be replaced every few hours?  I've been using the
     same eraser for YEARS on almost a daily basis and it still works fine!

     I don't have any problem with heat buildup, and I have had very little
     problem erasing 16C5x parts with about 45 minutes exposure.  I might
     be able to go shorter, but I haven't done much experimenting in that
     area.