What Are Mirror Coatings?
Mirror coatings (also called flash coatings or reflective coatings) are metallic or dielectric layers applied to the front surface of a lens to reflect a portion of incoming light. They give the lens a reflective, mirror-like appearance and provide additional light reduction beyond what the base tint alone offers.
How Mirror Coatings Work
Mirror coatings are applied using vacuum deposition, where thin layers of metallic or metallic oxide materials are evaporated and deposited onto the lens surface in a controlled vacuum chamber. The coating reflects light rather than absorbing it (as tints do), providing an additional layer of light reduction.
Two intensity levels are common:
- Flash mirror: A subtle, partially reflective coating that adds a hint of mirror effect while still allowing the wearer's eyes to be somewhat visible. Reflects approximately 10-20% of light.
- Full mirror: A dense, highly reflective coating that conceals the wearer's eyes. Reflects 25-60% of light.
Mirror Coating Colors
| Mirror Color | Effect | Popular Use |
|---|---|---|
| Silver | Classic reflective look, neutral tone | General purpose, classic style |
| Gold | Warm reflective appearance | Fashion, warm-tone frames |
| Blue | Cool, modern appearance | Fashion, water sports |
| Green | Subtle, classic reflective look | Aviator style, general outdoor |
| Red/Pink | Bold, vibrant appearance | Fashion, sport |
| Multi-color (rainbow) | Shifts color with viewing angle | Fashion statement |
Mirror coatings REFLECT light (bounce it back), while tints ABSORB light (convert it to heat). The total light reduction of a mirrored sunglass lens is the combination of both: the base tint absorption plus the mirror reflection. A 50% gray tint with a 20% mirror coating transmits only about 40% of light.
Benefits
- Additional light reduction: Beyond the base tint alone
- Eye concealment: Others cannot see the wearer's eyes, providing privacy
- Cosmetic appeal: Distinctive, fashionable appearance
- Reduced heat: Reflected light does not heat the lens (unlike absorbed light from tints)
- High-altitude/snow use: Extra protection in extremely bright conditions
Limitations
- Durability: Mirror coatings are on the exposed front surface and can scratch, chip, or wear off over time
- Cost: Adds to the overall lens price
- Not for indoor use: Mirror coatings combined with tints are too dark for indoor or low-light conditions
- Back-surface reflections: Light can enter from behind and reflect off the back surface of the lens into the eye; AR coating on the back surface helps
For the best mirrored sunglass lens, apply mirror coating on the front surface and AR coating on the BACK surface. The back-surface AR eliminates annoying reflections from light entering from behind (off the wearer's face or from peripheral light sources), which is a common complaint with mirrored sunglasses.
Assuming mirror coatings alone provide adequate sun protection. Mirror coatings reflect only a portion of light; the base tint does most of the work. A mirror coating without an underlying tint would be too light for outdoor use. Additionally, UV protection must still be verified independently, as mirror coatings do not necessarily block UV radiation.
Key Takeaways
- Mirror coatings reflect incoming light, providing additional brightness reduction beyond tints
- Flash mirrors are subtle; full mirrors conceal the wearer's eyes
- Available in various colors (silver, gold, blue, green, red, rainbow)
- Applied to front surface via vacuum deposition; back-surface AR recommended
- Mirror alone is not sufficient; must be combined with base tint and UV protection