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Marc Roessler

Additional UV Filtering on HMIs - required?

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Hi,

 

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?

 

Kind regards,

Marc

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There are various wavelengths of UV, some of which are harmful and some aren't. The stuff that makes your clothes glow in a nightclub is, in the main, in the latter category.

 

If the cover glass is intact I would suspect you're OK, but there are various services out there which will check these things for you with a UV hazard measurement device. You may not like the cost.

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Thanks Phil, good point! That's also a good possible explanation what LEE's UV filters are for: for filtering that last little bit of long wave UV that makes UV active materials glow.

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My understanding is that they're to minimise haze and blueness due to UV, especially outside studio windows where ND may not cut the UV as much as it cuts visible light, and to prevent fading of artwork and the like.

 

I once asked Lee (I think, perhaps one of the others) whether their UV filter gels would be suitable for ensuring eye safety in an application of 35W miniature metal halide lighting - essentially, the same thing you see in car headlights. The response was "Possibly, but we wouldn't go anywhere near guaranteeing it."

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My understanding is that they're to minimise haze and blueness due to UV, especially outside studio windows where ND may not cut the UV as much as it cuts visible light, and to prevent fading of artwork and the like.

 

I once asked Lee (I think, perhaps one of the others) whether their UV filter gels would be suitable for ensuring eye safety in an application of 35W miniature metal halide lighting - essentially, the same thing you see in car headlights. The response was "Possibly, but we wouldn't go anywhere near guaranteeing it."

 

Clear poly will protect from the harmful UV- so if it is has a plastic lens/cover yer protected.

 

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