Incandescent bulbs used for photo printing usually only have about 3.5 hours of total life, when used normally i.e. the bulb turning on and off (which increases its degradation). I used to use a current timer that I took out of an old server back in the late 80's and put it in between the timer and bulb so I could keep track of the age/life of the bulb. Going from an old bulb to a new one gave me a 1 grade of contrast and 1 stop speed. This comes in handy when doing series of images and you don't want to change in the middle of it, and thus change the look of the series.
Hope this helps |