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Coatings and Scratch Resistance
Scratch on the window can greatly reduce the performance of the EM20-85. It is suggested to use abrasion resistant
window material or coating.
The following introduces two commonly-used types of coatings:
• Anti-reflection coatings: Anti-reflection (AR) coatings can be applied to window surfaces to reduce reflected light from
the window back into the engine. Multi-layer AR coatings on windows help to achieve less than 0.5% reflectance and
covered wavelength is 400-780nm.
• Scratch resistance coatings: Scratch resistance coatings require a degree of greater than 5H in its hardness. Coatings
can be applied to plastic surfaces to increase the surfaces' abrasion and scratch resistance.
Both tempered glass and plastic windows can be AR coated. However, it is easier and more cost-effective to put an AR
coating on the glass than on the plastic.
The AR coating specifications below should be met when using an AR coated window.
Single side AR coating: 92% minimum transmittance within spectrum range from 420 nm to 730 nm.
Double side AR coating: 97% minimum transmittance within spectrum range from 420 nm to 730 nm.
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