Hi,
As an interim measure, while waiting to build my darkroom, I want to use a bare bulb as my light source for contact printing, I will be rigging up a holder for filters but was wondering if it would be an advantage (or desirable) to include a diffuser?

I can set it up to use either a 15w incandescent globe or a variable wattage halogen/ dichroic bulb.

Any suggestions or ideas?

Edward Weston used a clear light bulb with what looks like a handkerchief or some toilet paper over it. He could also adjust the height to change the exposure. An ordinary frosted bulb should do.

Cole Weston used to demonstrate his father's technique by putting one or more layers of toilet tissue over the bulb to attenuate the light.

If the bulb is sufficiently far away from the contact print frame no diffuser is necessary when using an ordinary incandescent bulb.

I use a PAR/floodlight over a contact print frame,
and lay piece of milk glass on the frame.

You can also buy the plastic diffusing sheets meant for overhead florescent fixtures. These are plastic / acrilic and are pretty easy to score and cut to size. Just don't place it directly on the glass of your frame because you may get a funny pattern in your print.