Originally Posted by colrehogan
Since your exposures are going to last a few minutes at least, simply add 10 seconds to the exposure time. This allows the bulb time to ramp up to full output. With BL or BLB tubes they don't need to be left on all the time.
Ideally, a light integrator sensitive to UV such as an OLIX can be used in place of a standard timer. This will eliminate variations in output due to bulb temperature and line voltage. This will give you the most repeatable results.
However an old fashioned Gray-Lab timer will work adequately unless you have really bad house current.