It is my understanding that if you are able to reduce the voltage by even ten percent that the bulb life is greatly extended. I use a condenser enlarger and I use a constant aperture and time. I control my exposure time thru adjusting the bilbs brightness. To control the voltage I bought a lamp dimmer from Home Depot...approx. $10.00 It works very nicely. I also use one on a bulb for viewing wet prints so that the brightness of my print examination is similar to the conditions in which they will be displayed.