Tints and driving
- BS EN ISO 12312-1:201380 attributes filters for sunglare use into five groups, according to their range of luminous transmittance (Tv).
|Filter category||Description||Range of luminous transmittance in the visible spectral range|
||Clear or very light tint||from over 80% to 100%|
|1||light tint||from over 43% to 80%|
|2||medium tint||from over 18% to 43%|
|3||dark tint||from over 8% to 18%|
|4||very dark tint||from over 3% to 8%|
- Filters suitable for road use and driving shall be of categories 0, 1, 2 or 3 and in addition:
- the spectral transmittance of filters suitable for road use shall be not less than 0.2 x Tv for wavelengths between 475 and 650 nm, and
- the relative visual attenuation coefficient Q of filters of categories 0, 1, 2 and 3 suitable for driving and road use shall be not less than 0.8 for red and yellow signal lights, not less than 0.6 for yellow, green and blue signal lights.
- Sunglass filters with a luminous transmittance of less than 75% are not suitable for road use in twilight or at night.
80 British Standards Institution (2013) BS EN ISO 12312-1:2013: Eye and face protection. Sunglasses and related eyewear. Sunglasses for general use. Para 532 [College members only], [accessed 31 Oct 2013]