NeXe Lights
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| So I've heard that polycarbonate and acrylic are both more impact resistant than glass. Now, of course, both plastics don't hold up well with HID wattages above 250. But why didn't they design some sort of UV-resistant coating for polycarbonate to make it UV-proof like glass? If they did this, polycarbonate would probably be the go-to choice for wattages of 250 and under.
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Baked bagel 11
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| 400, and even 700w Acrylic lenses were used over here in the Optispec (250-700w MBF) as well as numerous 400w HPS lights. Acrylic is pretty good, provided that it isn't too close to the lamp.
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Collects lanterns from Australia, UK and the USA.
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NeXe Lights
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| Ah, well, that updates the heat resistant category. But why did they not develop some sort of coating, primarily for polycarbonate, to block and absorb UV before it hit the plastic? That would make using strong plastics like polycarbonate much more viable for the long term.
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Baked bagel 11
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| That, I'm not sure. Many lights (such as the Sylvania Roadster) had a "standard" bowl rated to 250w and a 400w bowl. There was also usually an option for a polycarbonate "vandal resistant" bowl. This suggests that acrylic bowls are weaker than polycarbonate bowls.
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NeXe Lights
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| Polycarbonate is indeed stronger than acrylic. I did a quick Google search, and polycarbonate is up to 250 times more impact resistant than glass and up to 30 times more impact resistant than acrylic. Additionally, polycarbonate is 6 times lighter than glass. However, it is not UV proof like acrylic and glass.
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RRK
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| Polycarbonate goes yellow over time. AFAIK this can be reduced by some stabilizing additives like antioxidants *in the plastic volume*. Probably not 100% effective and is a subject of manufacturer know-how.
Acrylic does not yellow, but is fragile and has relatively low melting point.
Note good ol' mineral glass can withstand high temperature, is not particularly expensive and of course does not yellow at all.
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dor123
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@RRK: What is the plastic that is common for making LED panels that degrades fast?
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Please forgive me if my choice of my words looks like offensive, while that isn't my intention.
I only working with the international date format (dd.mm.yyyy).
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RRK
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| I won't say the plastic is degrading fast considering that extreme loading it experiences in the vicinity of semiconductor crystal. As far as I heard it is either silicone or epoxy. Acrylic is popular for external beam-forming elements ('waveguides')
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dor123
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@RRK: I meaning degradation like this: https://www.lighting-gallery.net/gallery/displayimage.php?pos=-223562@AsXSn said to me that this can't be acrylic because it is UV resistant, and think it is polycarbonate.
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« Last Edit: June 13, 2025, 10:34:20 AM by dor123 »
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I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.
I only working with the international date format (dd.mm.yyyy).
I lives in Israel, which is a 220-240V, 50hz country.
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RRK
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| For external light-diffusing material of a LED panel a manufacturer may choose pretty whatever cheapo material he wishes. Any cheap milky plasic sheet. Of course it can yellow over time even in sunlight.
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NeXe Lights
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| Really, the only advantage that polycarbonate has over glass is that it's more impact resistant, but this advantage is lost after a few years when it yellows. Which is why I think they should have developed a way to completely block out the UV from hitting the polycarbonate, as to make it better than glass in every way aside from heat resistance.
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RRK
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| Polycarbonate is rather expensive so I doubt it will be used as a diffuser sheet outside some special application. May be even some cheapo ABS sheet here. BTW may be LEDs themselves got yellowed and not an outside plastic. A picture of the same luminaire in the daylight will give a clue.
A common approach in a material science is not to attempt to filter UV on the surface, but to stop a cascade of unwanted chemical reactions that happens when light hit the plastic. Something like antioxidants that are catching free radicals generated when energetic light quantums are absorbed by plastic molecules and preventing them to form dark colored compounds. And even some special "energy sponge" compounds that help plastic molecules to dissipate the energy without breaking and forming free radicals.
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« Last Edit: June 13, 2025, 11:23:18 AM by RRK »
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dor123
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See here . But I think that the degrading is of the diffuser, not the LEDs, as it is occurs at the center of the panels, and the LEDs are on the edge of the panel inside a LED strip.
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I"m don't speak English well, and rely on online translating to write in this site.
Please forgive me if my choice of my words looks like offensive, while that isn't my intention.
I only working with the international date format (dd.mm.yyyy).
I lives in Israel, which is a 220-240V, 50hz country.
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Michael
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| Toughened glass is more heat and impact resistant than acrylic (PMMA). Acrylic has slightly better transparency than glass and Polycarbonate.
Polycarbonate (PC) is the best solution for vandal proof lighting but lacks on transparency compared to glass and PMMA especially when not UV stabilized. It becomes brittle over the time of use.
What I’ve learned during my years at Schréder is that the best compromise is toughened glass and that’s why so many Schréder lanterns used that material for street lighting like for example the Sapphire, Onyx, DZ and EZ range.
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AsXSn
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| About PC yellowing reasons, except UV, polycarbonate are too not resistant for longer exposure to heat sources like HID lamps, it also yellowing with HPS which UV radiation is extremely small or nothing, I know yellowing process by heat exposure with HPS depends from the lamphouse size, lamp wattage and ofc polycarbonate quality.
Acrylic (PMMA) also sometimes went milky when was overheated or sometimes when quality was not enough by issues on the production process step, by that it went milky when even working on not that extremely conditions
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