These are xenon filled lamps, and are the kind used in strobe lights.  Smaller versions are used for camera flashers.

Compared to the flash that a strobe or a camera puts out, this experiment was a bit of a disappointment.  I put the lamps under just enough water to cover them.  They were very dependent on the location in the oven, lighting only in a small area near the magnetron outlet.  This is the brightest photo I could get using 5 lamps.