I'm curently restoring a second hand 1200W HMI (open face) that I bought.
It has the protection glass in place, but testing it it appeared to me that white paper that is hit by its light seemed to have some bluish glow. Knowing some papers have UV active whiteners, for checking I added a LEE UV filter, and lo and behold the blue glow of the paper is gone!
This means this HMI puts out quite some UV even with its glass in place!
Now the question is: is this still within the normal range or should I replace the glass? How do I find out if it is within the normal range? I've used HMIs a few times (also bigger ones, 4K fresnel) but never noticed this effect with other HMIs. Or is some UV to be expected? How much?