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Comparison

LONGLASSTING

As one of the world's most experienced designer and manufacturer of optical glass components for the lighting industry, Auer Lighting highly recommends glass for LEDs. This is due to its features concerning environmental resistivity, transparency and the ability to withstand temperatures well above 300 °C without degradation. In particular, the last point is becoming of increasing interest as the power of LEDs is rising and thus producing more heat. Optics made from plastic materials will only stay stable for much lower temperatures, limiting already the potential performance of high-power lighting systems. The advantages of glass open up the possibility to use more powerful light sources that bring LED lighting to a whole new brightness level.

Properties of optical materials

Property Glass SUPRAX 8488 PMMA PC Silicone Remarks
Density (g/cm³) 2.31 1.18 1.20 1.02  
Water absorption (weight %) no 0.6 - 2.0 0.1 - 0.3 0.2 acc. to ISO 62
Thermal expansion
coefficient (10-6/K)
4.1 80 70 250 - 345  
Thermal conductivity
(W/(m K))
1.20 0.19 0.21 0.31  
Heat capacity
(J/(g K))
0.80 1.20 1.17 1.37 @ 25 °C
Flammability (mm/min)
(class)
no 25 (HB) 2.5 (VO) HB-V1 UL 94
Chemical resistivity ++ - 0 +  
Short-time operating
temperature (°C)
450 93 130 260  
Permanent operating
temperature (°C)
400 <80 <110 150  
Light transmission
(%)
92 92 89 91 D = 3 mm
Refractive Index 1.482 1.492 1.585 1.410 @ 25 °C
Fresnel losses (%) 3.8
7.5
3.9
7.6
5.1
9.9
2.9
5.7
one surface
two surfaces
Thermo-optic coefficient
dn/dT (10-4/K)
0 -1.1 -1.1 -5.0  
Abbe number 65 59 31 50 νd
Coatability ++ 0 0 -  
UV resistivity ++ 0 - +  
Cleanability ++ - - -  
Possible feature size 0 + + +  
Yellowness index 0 8 9 1 30 years ASTM
E313

Glass - The Perfect Companion for long-lasting LEDs

Glass is the perfect companion for long-lasting LEDs, due to its durability as well as versatility in shape and features. And temperature is no problem for glass. It can be easily coated (to enhance initial performance) and cleaned (to keep that initial performance).

From the cost side glass optics can reach competitive pricing levels if adequate design is accounted for, especially for specialized and/or qualitative optics. A simple copy of existing plastic optics will not do so.

Why glass has been put in second place so far in the LED world is not easily understandable. But it shows so many valuable and interesting features that no one can afford to ignore it any longer.