Camera PV 2007 » Digital Camera » restore yellowed diffusers
restore yellowed diffusers
Question:
> The diffusers in overhead fluorescent fixtures will soften and fall out in
Acrylic, polycarbonate, and vinyl have already been mentioned … but I thought that most overhead fluorescent fixtures used frosted polystyrene diffusers. Or is polystyrene a type of vinyl? Tim.
Response:
> The diffusers in overhead fluorescent fixtures will soften and fall out in > Acrylic, polycarbonate, and vinyl have already been mentioned … > but I thought that most overhead fluorescent fixtures used > frosted polystyrene diffusers. > Or is polystyrene a type of vinyl? > Tim.
Good point. At home improvement stores, I see a selection of the styrene and acrylic replacement diffusers. The styrene is lower cost, but it is more brittle and prone to cracking. Styrene and vinyl are different types of plastics. John
Response:
I’m going to opt for the old sandpaper method, that is if the yellowing is on the surface, and not all the way through. Then if sandpapering goes well, I will buy this clear UV protective spray paint. I don’t know how this spray paint will hold up due to the heat from the bulbs being just 3" away from the plastic, nor do I know if the yellowing if totally due to UV, and all that heat is not the culprit. I quess it’s worth a shot. I’ve looked around with companies that specialize in replacement diffusers, but I am unable to locate a suitable replacement. My light fixtures are very old, they were first installed in 1986. They are badly yellowed to the point that if I take a picture with my digital camera without flash, The pictures come out in a bright shade of orange, and most other colors are washed out. And It’s getting to the point where I must install twice the total wattage of bulbs than would otherwise be needed. If all esle fails, I will throw the damn things out and live with bare bulbs, or maybe replace the fixtures.
Response:
One other thought. Any sign company that makes plastic sign faces could mold white diffusing acrylic to the shape that you need. It’s almost a do-it-yourself project if you have a source of radiant heat – or an oven big enough for the pieces. Rhom and Haas (Plexiglas) used to have some nice handbooks about working sign plastic and perhaps they are on-line somewhere. Simple shapes can be molded using a wood-block mold and letting the plastic sag onto the shape; but I don’t have experience with more complicated pieces. Terry McGowan
– Hide quoted text — Show quoted text -> I’m going to opt for the old sandpaper method, that is if the yellowing is on > the surface, and not all the way through. Then if sandpapering goes well, I > will buy this clear UV protective spray paint. I don’t know how this spray > paint will hold up due to the heat from the bulbs being just 3" away from the > plastic, nor do I know if the yellowing if totally due to UV, and all that > heat is not the culprit. I quess it’s worth a shot. > I’ve looked around with companies that specialize in replacement diffusers, > but I am unable to locate a suitable replacement. My light fixtures are very > old, they were first installed in 1986. They are badly yellowed to the point > that if I take a picture with my digital camera without flash, The pictures > come out in a bright shade of orange, and most other colors are washed out. > And It’s getting to the point where I must install twice the total wattage of > bulbs than would otherwise be needed. If all esle fails, I will throw the > damn things out and live with bare bulbs, or maybe replace the fixtures.
Response:
Acrylic is widely used for fluorescent commercial lighting diffusers, but I don’t know about HID. I’ve only seen acrylic refractors used for outdoor HID security lights. Terry McGowan
– Hide quoted text — Show quoted text -> Do they make acrylic heat/flame resistant for light diffusers? Standard > acrylic’s low distortion temperature would limit it’s use where the > temperature is high such as in HID fixtures. Unlike vinyl and polycarbonate, > standard acrylic is free burning if it ignites. > Engineers using acrylic in diffuser design should be careful when developing > retaining systems for the fixture. If screw fastened and the maintenance > person over-tightens a screw, it will crack. With some loss to it’s optical > properties I know acrylic can be toughened. I’m not sure about heat and > flame resistance. > The diffusers in overhead fluorescent fixtures will soften and fall out in > the event of fire rather than starting secondary fires by dripping burning > plastic on to flammables. In this case of these relatively cool fluorescent > lamps, heat/flame resistance is not an issue. I’m more concerned with HID > fixtures and the possibility of fires due to failures within the fixtures > itself. > I’ve been very weary of flammable plastics when used in high temp electrical > devices since a plastic electric space heater failed and burst into flames. > Here’s that story: http://home.att.net/~jriegle/heatfire.htm > John > It’s usually better to toss/replace brittle and yellowed diffusers from my > experience. There are several companies who specialize in such > replacements. > Cheaper diffusers are typically made from vinyl and that material is > notorious for quickly yellowing. Light and heat alone will do it and UV > speeds up the process. Even understanding the cost issues, I’ve never > figured out why lighting manufacturers use it. Surely the yellowing is a > source of major customer claims and complaints. > Polycarbonate is another widely-used lighting plastic that also yellows > quickly; but there are UV-stabilized versions which last longer. > Polycarbonate ("Lexan") is tough and strong and so is widely used in > outdoor > and vandal-resistant lighting fixtures; but when it was first used some > years ago in security and roadway fixtures, manufacturers recommended > replacing the lenses every 6 months! Needless to say, users (particularly > electric utilities) didn’t think much of the idea. Hopefully they last > longer today. > I believe that the best plastic lighting material remains acrylic > ("Plexiglas"). It doesn’t yellow, lasts for years and has great diffusing > properties. A major use is faces for transilluminated plastic signs. > It’s > sometimes a little more costly than vinyl and other plastics; but by the > time UV and other coatings are added to the cheaper stuff, the cost is > about > the same. > Frankly, considering the time involved, the chemicals that would be needed > and the loss in structural strength that would probably result, I don’t > think that trying to renew cheap plastic makes any sense. Polycarbonate, > because it is relatively expensive, might be worth it if indeed the > yellowing is in the surface layers. > Terry McGowan
Response:
Do they make acrylic heat/flame resistant for light diffusers? Standard acrylic’s low distortion temperature would limit it’s use where the temperature is high such as in HID fixtures. Unlike vinyl and polycarbonate, standard acrylic is free burning if it ignites. Engineers using acrylic in diffuser design should be careful when developing retaining systems for the fixture. If screw fastened and the maintenance person over-tightens a screw, it will crack. With some loss to it’s optical properties I know acrylic can be toughened. I’m not sure about heat and flame resistance. The diffusers in overhead fluorescent fixtures will soften and fall out in the event of fire rather than starting secondary fires by dripping burning plastic on to flammables. In this case of these relatively cool fluorescent lamps, heat/flame resistance is not an issue. I’m more concerned with HID fixtures and the possibility of fires due to failures within the fixtures itself. I’ve been very weary of flammable plastics when used in high temp electrical devices since a plastic electric space heater failed and burst into flames. Here’s that story: http://home.att.net/~jriegle/heatfire.htm John
– Hide quoted text — Show quoted text -> It’s usually better to toss/replace brittle and yellowed diffusers from my > experience. There are several companies who specialize in such > replacements. > Cheaper diffusers are typically made from vinyl and that material is > notorious for quickly yellowing. Light and heat alone will do it and UV > speeds up the process. Even understanding the cost issues, I’ve never > figured out why lighting manufacturers use it. Surely the yellowing is a > source of major customer claims and complaints. > Polycarbonate is another widely-used lighting plastic that also yellows > quickly; but there are UV-stabilized versions which last longer. > Polycarbonate ("Lexan") is tough and strong and so is widely used in outdoor > and vandal-resistant lighting fixtures; but when it was first used some > years ago in security and roadway fixtures, manufacturers recommended > replacing the lenses every 6 months! Needless to say, users (particularly > electric utilities) didn’t think much of the idea. Hopefully they last > longer today. > I believe that the best plastic lighting material remains acrylic > ("Plexiglas"). It doesn’t yellow, lasts for years and has great diffusing > properties. A major use is faces for transilluminated plastic signs. It’s > sometimes a little more costly than vinyl and other plastics; but by the > time UV and other coatings are added to the cheaper stuff, the cost is about > the same. > Frankly, considering the time involved, the chemicals that would be needed > and the loss in structural strength that would probably result, I don’t > think that trying to renew cheap plastic makes any sense. Polycarbonate, > because it is relatively expensive, might be worth it if indeed the > yellowing is in the surface layers. > Terry McGowan > I’ve done my homework searching google before posting this. Most people > who > ask about removing yellow from plastic ask as if the yellowing is just > dirt > or a stain, and are looking for a special cleaner. I raed through the > replies and conclude that the yellowing is caused by UV exposure which > destroys the plastic at the molecular level. But with the case as > lighting > fixtures, the added heat from the indcandescent bulbs has a compounding > effect. The only way to remove the yellow is to remove the damaged > plastic > somehow. The damaged layer is usually very thin, unless it is VERY old > and > the plastic and got brittle streight through. > Q: Anyone out there got any ideas on solvents and things that can remove > the > dead plastic layer? (without distorting or scraping) > I would like to know if there’s any sort of product I can coat my > diffusers > with to block further UV from additional yellowing. > Interesting notes come from people who have old computers that got very > yellowed, but new plastics today usually have UV inhibitors so yellowing > is > now seldom a ploblem due to UV exposure. Other sources of yellowing > include > smokers which can be washed off, using strong chemicals to clean, and some > very old plastics can yellow even from sitting in dark storage.
Response:
<< I would like to know if there’s any sort of product I can coat my diffusers with to block further UV from additional yellowing. >> Paint. An acrylic based paint like Krylon has few problems with UV. Thats why airplane windows are made from it and the better auto paints are acrylic based. The pigment in the paint should be a good blocker from further UV damage. Test a bit of the plastic before painting to ensure compatibility. Good luck. Joe
Response:
It’s unlikely that you’ll find a paint that will block UV without also blocking visible-light, which probably isn’t what you want to do to a plastic diffuser.. In my office, they use what looks like aluminized mylar grills, instead of solid transparent panels. I’d try that, or sandblasting. – Hide quoted text — Show quoted text -> << I would like to know if there’s any sort of product I can coat my diffusers > with to block further UV from additional yellowing. >> > Paint. An acrylic based paint like Krylon has few problems with UV. Thats why > airplane windows are made from it and the better auto paints are acrylic based. > The pigment in the paint should be a good blocker from further UV damage. Test > a bit of the plastic before painting to ensure compatibility. Good luck. > Joe
Response:
It’s usually better to toss/replace brittle and yellowed diffusers from my experience. There are several companies who specialize in such replacements. Cheaper diffusers are typically made from vinyl and that material is notorious for quickly yellowing. Light and heat alone will do it and UV speeds up the process. Even understanding the cost issues, I’ve never figured out why lighting manufacturers use it. Surely the yellowing is a source of major customer claims and complaints. Polycarbonate is another widely-used lighting plastic that also yellows quickly; but there are UV-stabilized versions which last longer. Polycarbonate ("Lexan") is tough and strong and so is widely used in outdoor and vandal-resistant lighting fixtures; but when it was first used some years ago in security and roadway fixtures, manufacturers recommended replacing the lenses every 6 months! Needless to say, users (particularly electric utilities) didn’t think much of the idea. Hopefully they last longer today. I believe that the best plastic lighting material remains acrylic ("Plexiglas"). It doesn’t yellow, lasts for years and has great diffusing properties. A major use is faces for transilluminated plastic signs. It’s sometimes a little more costly than vinyl and other plastics; but by the time UV and other coatings are added to the cheaper stuff, the cost is about the same. Frankly, considering the time involved, the chemicals that would be needed and the loss in structural strength that would probably result, I don’t think that trying to renew cheap plastic makes any sense. Polycarbonate, because it is relatively expensive, might be worth it if indeed the yellowing is in the surface layers. Terry McGowan
– Hide quoted text — Show quoted text -> I’ve done my homework searching google before posting this. Most people who > ask about removing yellow from plastic ask as if the yellowing is just dirt > or a stain, and are looking for a special cleaner. I raed through the > replies and conclude that the yellowing is caused by UV exposure which > destroys the plastic at the molecular level. But with the case as lighting > fixtures, the added heat from the indcandescent bulbs has a compounding > effect. The only way to remove the yellow is to remove the damaged plastic > somehow. The damaged layer is usually very thin, unless it is VERY old and > the plastic and got brittle streight through. > Q: Anyone out there got any ideas on solvents and things that can remove the > dead plastic layer? (without distorting or scraping) > I would like to know if there’s any sort of product I can coat my diffusers > with to block further UV from additional yellowing. > Interesting notes come from people who have old computers that got very > yellowed, but new plastics today usually have UV inhibitors so yellowing is > now seldom a ploblem due to UV exposure. Other sources of yellowing include > smokers which can be washed off, using strong chemicals to clean, and some > very old plastics can yellow even from sitting in dark storage.
Response:
I’ve done my homework searching google before posting this. Most people who ask about removing yellow from plastic ask as if the yellowing is just dirt or a stain, and are looking for a special cleaner. I raed through the replies and conclude that the yellowing is caused by UV exposure which destroys the plastic at the molecular level. But with the case as lighting fixtures, the added heat from the indcandescent bulbs has a compounding effect. The only way to remove the yellow is to remove the damaged plastic somehow. The damaged layer is usually very thin, unless it is VERY old and the plastic and got brittle streight through. Q: Anyone out there got any ideas on solvents and things that can remove the dead plastic layer? (without distorting or scraping) I would like to know if there’s any sort of product I can coat my diffusers with to block further UV from additional yellowing. Interesting notes come from people who have old computers that got very yellowed, but new plastics today usually have UV inhibitors so yellowing is now seldom a ploblem due to UV exposure. Other sources of yellowing include smokers which can be washed off, using strong chemicals to clean, and some very old plastics can yellow even from sitting in dark storage.