The 120-volt PH-140 is rated for 35 hours of average bulb-on time.

http://www.replacementlightbulbs.com/lampph140_75w.html (120-volt version)


According to this, the 230-volt PH-1400 is rated for 50 hours.

http://store.khbphotografix.com/PH14...mp-6-pack.html ($15/bulb)