None, because the International Space Station don’t have any spares on board. But they sure could use some. The Mainichi Daily News reports that almost half the fluorescent lamps on Kibo, the Japanese module on the station, have burned out.

As of Friday last week, only one of the four lamps in the storage room and 11 of the 17 in the main experimentation room were working.

The fluorescent lamps used on the ISS were produced by a U.S. company in 1997. As many of the lamps in other modules have also burned out, all the spares aboard the space station have been used.

Tetsuro Yokoyama, sub-manager of the Kibo operation team, said he suspects that the quality of vacuum in the lamps has decreased while aboard the ISS.

Six new lamps will be sent up on a shuttle mission in November: LED systems are being developed as a long term replacement, but won’t be ready til 2010

Hat tip: NasaWatch

Added value: Wikipedia entry on lightbulb jokes