Why do enlarger timers turn the safelight off during exposure?
I have a gralab timer and it turns off the safelight during exposure. I always wondered about this, because it makes it hard to align the easel since when the image is on, the rest of the room is dark and vice versa. I was considering bringing in a small auxiliary safelight just so that I could see to position the easel with the image on, but why not just plug my safelight directly into the wall and leave it on all the time? I went to the darkroom at the university and they had whole-room safelights that obviously don't turn off during exposure. What's the rationale for the enlarger timer behavior?