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What’s the difference of PC,PMA,Toughened glass?

Choosing what lenses of your LED light bar is what you may ignore.Len is the most possible neglect one when you buy a
LED work light or LED light bar.Usually there are 3 types of lenses,PMMA,PC and toughen glass.Below is detail.
PMMA(poly methyl methacrylate), also know as plexiglas,acrylite,.Advantage:Good light transmission, Excellent resistance to many chemicals, At the same strength and durability, it is only half the weight of glass, Despite the hard conditions of heat, cold, sunlight, and humidity, pmma maintain their original appearance.
Disadvantage:not high-temperature,not impact resistance as PC
Toughen glass:
Advantage:good light transmission,high-temperature resistance,impact resistance
Disadvantage:heavy weight,easily to broke when drop
Improved-clarity PC materials offer high transparency that can provide approximately 90-92% light transmission, nearly comparable to that of PMMA. This capability makes them suitable for HB LEDs used to retrofit high-intensity discharge (HID) fixtures and fluorescents, as well as for flashlights and automotive headlamps.
When diffusion is required, specialized PC resins can provide a broad spectrum of light management to customize performance without compromising forward light transmission .Different diffusion technologies can provide narrow-angle or wide-angle light scattering, while diffusers plus opacifiers combine translucent scattering with wide-angle light scattering.
PC manufacturers such as SABIC may be able to tailor diffusion properties to meet customer requirements. Diffusion-based PC products also provide a system solution that could potentially be more effective and cheaper than a diffuser film that is often used in such applications.
Anti-dust capability helps to maintain long-term reflectivity performance. At the same time, although the PC grades are highly filled, they retain their excellent mechanical properties. Finally, the design freedom provided by PC facilitates the creation
of diverse reflector shapes. In contrast, anti-dust PMMA materials cannot deliver equivalent mechanical performance and do not meet UL94 V0 flame retardancy requirements.

2.PC life span
Improved-clarity PC resins provide an array of performance properties that help LED lights operate effectively over their full useful life. First, PC is renowned for outstanding impact resistance that surpasses the performance of PMMA by a factor of 10 in typical lab or practical impact measurements and that of glass by a factor of 30 (Fig. 2).

In outdoor lighting, transparent, weatherable PC resins offer a welcome alternative to both glass and PMMA because they combine high impact performance to protect the solid-state LED from vandalism and other threats, meet stringent UL requirements for weatherability and flame retardancy and optimize forward transmission of light. In contrast, breakable glass does not provide sufficient impact protection, and PMMA does not meet UL94 V0 requirements.
Heat aging, another aspect of LED life span, is becoming even more important as high-brightness LEDs (HB LEDs) with higher lumen outputs place added stress on optical components. Improved-clarity PCs can handle extended exposure to temperatures of 110°C to 130°C, which is a developing trend for HB LEDs, while retaining their mechanical and optical properties.
3. Polycarbonate vs. PMMA
The increasing adoption of LED lighting creates applications for polycarbonates that were previously the preserve of materials such as glass and metal. For instance, because LEDs emit “cold” light without infrared (IR) radiation, thermal stress on the lamp components is reduced, making it possible to replace glass lenses with those made of transparent thermoplastics, most notably polycarbonate and polymethyl methacrylate (PMMA). PC and PMMA have already been applied to LED lamps and luminaires, especially as parts of housings or transparent covers. PC and PMMA components can be lighter and thinner than glass, and offer design flexibility. In addition, the components have been cost effectively scaled to production volumes using injection-molding processes. Relative to PMMA, polycarbonate benefits from greater heat resistance, higher impact strength and increased resistance to breakage. PC is also more flame-retardant. Benefits of PMMA over PC include its higher light transmission (> 92%) and better resistance to UV radiation.
Special grades of PC have a light transmission in the visible-wavelength range just under 90%, but they absorb radiation in the UV as well as mid- and far-IR regions. UV exposure will damage standard grades of PC, resulting in an increasing yellowness that impairs the transparency of lenses and covers for lighting fixtures. To counter this phenomenon, a new infusion process has been developed to concentrate UV protection at the surface of PC products (see sidebar).

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