Sunglass Light Transmission Limits Ban Certain Lenses for Driving

Sunglass manufacturers sometimes label lenses with the warning “Not suitable for driving and road use.” The notice refers to the lens’s light‑transmission rating, which is classified from 0 (over 80 % light passed) to 4 (only 3–8 % passed). Lenses in categories 3 and 4 are intended for very bright environments such as high‑altitude, snowy or desert conditions and are too dark for road use because they hinder the driver’s ability to see traffic signals and road markings.

Optical standards require that lenses let enough light through to recognize red, yellow, green, and blue signals. Lenses transmitting less than 75 % of light are considered unsafe for night or twilight driving. Neutral gray or brown lenses are recommended for most drivers, as they reduce glare without distorting colours, whereas strongly coloured lenses (blue, red, etc.) can impair signal recognition. The article cites Ray‑Ban and Oakley as brands that have used the “not suitable for driving” label on certain models.