Yellowed. Polycarbonate lenses here always yellow badly with MV lamps. Even with HPS after so many years. For some reason they don't use enough UV inhibitors in the plastic. Most lenses here are acrylic anyway.
They probably didn't care, since if it yellowed it would need to be replaced. If the lens remained fine after decades of use there would be no market for replacements. That's my thinking anyway. Not sure really. In my opinion, glass should be used for all cobraheads except 50-150W HPS, where acrylic is fine. Acrylic works for 100 and 175w MV too, but I wouldn't use any plastic with MH lamps since lamp explosions send shards of glass into the lens and will slightly melt into it with plastic. At least with glass lenses all the particles wipe out fairly easy.
Yeah, lighting and planned obsolescence always went hand in hand, starting with Phoebus cartel in 1924...
As for MH lamps - a metallic mesh inside the bowl could probably be used to protect the plastic from the hot shards. AFAIK, some MH lamps for open luminaries have it inside.
The mesh would block light. However using open-rated lamps with a quartz shroud around the arc tube. Most people don't use them though because they cost more.
Yeah, they should just make open rated MH lamps so you don't get the people that put closed rated lamps in open fixtures to save a buck. You can do with with a lot of older MH fixtures.
Speaking of open lamps, I always chuckle a bit when I see the phrase "Type T self extinguishing lamps are commercially available" on the warning label of newer mercury lamps since I'm not sure when they last made those.
My 250w MV/MH GE lowbay has an acrylic refractor and a small mesh screen to contain explosions. It is so thin that it doesn't seem to block too much output.
My 250w MV/MH GE lowbay has an acrylic refractor and a small mesh screen to contain explosions. It is so thin that it doesn't seem to block too much output.
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As for MH lamps - a metallic mesh inside the bowl could probably be used to protect the plastic from the hot shards. AFAIK, some MH lamps for open luminaries have it inside.
Speaking of open lamps, I always chuckle a bit when I see the phrase "Type T self extinguishing lamps are commercially available" on the warning label of newer mercury lamps since I'm not sure when they last made those.