Both Home Depot and Lowe's sell halogen bulbs that are 100W "equivelent", but are 72W.

http://www.homedepot.com/p/Philips-7...1#.UeajI9KTiSo

Not to editorialize, but I use regular 150 tungsten bulbs as the "white" lights in my darkroom. You can't buy 100W, but 150W and 300W are readily available.