i would never use my bulbs for over a year. i had a pair of VHO's that i had to run for about 11 or 12 months + because i didnt have the money to spend on new bulbs (they are expensive at my lfs), and i forgot how long id had them. when i finally changed them, they were all blackened, and the new ones were 3x brighter easily. they just stop working as well after a while. JMO