Here is a great way to light your mirror ball, this uses an LED which has a 50,000 hour life expectency which is a lot longer then most bulbs you would use, American DJ Led Tri Spot is definatly the way you need to go.
Specifications:
High output DMX-512 LED Pinspot
3-watt 3-in-1 RGB ?TRI Color? LEDs produces a variety of color effects (Red, Green, Blue, Purple, Yellow, Cyan & White)
3 Operational Modes: DMX-512, Master/Slave, Sound Active
3 or 5 DMX Channel Modes
Slow to Fast Strobe
Dimming: 0-100%
Power consumption: 9W per unit
Long life LEDs (50,000 hr. rating)
Beam angle: 12-degree lens installed (also includes 6-degree lens in box)
Multi-voltage: AC 100V-240V 50/60Hz
Compatible with American DJ UC3 Controller (sold separately)
Dimensions Incl. bracket (LxWxH): 198x127x196mm
Weight: 1.2kg