Blinding glare can be potentially lethal when you're driving - particularly at speed. You can be dazzled by low sun or by bright light reflecting off snow, puddles, the car in front, or even your own bonnet.
Glare is frequently blamed as the cause of road traffic accidents, but the right pair of sunglasses can prevent it.
To clear up confusion about the type of sunglasses you should wear when driving, the AA asked The Federation of Manufacturing Opticians for advice.
Read on to find out what the law says and which sunglasses are best for driving in.
Clarity of vision
There are 2 essential requirements in lenses used for driving:
- Vision must remain clear.
- Sufficient light to let you see properly must get to your eyes.
Sunglasses sold for general use can be too dark for driving in. Plus, fashion frames could obscure your peripheral vision if they aren't the right style, so it's best to choose your shades carefully.
There are some sun lenses which are suitable for driving, and they fall into 2 main categories: 'fixed' and 'variable' tint.
Variable tint lenses
Generally known as 'photochromic' lenses, these change their tint density when exposed to certain kinds of light. Generally the brighter the light, the darker the lenses will turn.
Lenses that only react to UV light are not suitable for driving because car windscreens filter out UV, slowing and limiting the reaction of the lenses. You could find yourself driving with lenses too light as a result.
You need to look for lenses designed to react to visible light as well as UV to ensure they'll adapt to the varying light conditions when driving. Check with your optician to find the right ones.
Fixed tint lenses
These stay the same darkness no matter how sunny or dark it is. Fixed tint sunglasses are easy to find, and a fixed tint can be added to prescription glasses too.
Polarised lenses normally have a fixed tint and are specially-designed to reduce glare. They're particularly effective on light shining off wet roads.
Tint density
Not all tinted lenses are the same. They can be different colours and different densities, so you need to pick the ones which are suitable for driving.
- Tinted lenses are given a grading according to the density of the tint.
- All sunglasses should, by law, be labelled and show the filter category number.
- Lenses with light transmission less than 75% are unsuitable for night driving.
- Yellow tinted lenses are not recommended for night driving.
- Due to the light levels within the car, filter category 2 lenses which transmit between 18% and 43% of light are recommended for daytime driving.
- Filter category 4 lenses only transmit between 3% and 8% of light and are not suitable for driving at any time. Sunglasses with these lenses should, by law, be labelled 'Not suitable for driving and road use'.
This is what type of use each category of lens is suitable for:
| Light Transmission | Category | Use | Limitations |
| 80%-100% (clear) | 0 | indoors / overcast day | none |
| 43%-80% (light tint) | 1 | low sunlight | not for night driving |
| 18%-43% (mediium tint) | 2 | medium sunlight | not for night driving |
| 8%-18% (dark) | 3 | bright sunlight | not for night driving |
| 3%-8% (very dark) | 4 | exceptionally bright sunlight | not for day or night driving |
Graduated lenses
Some drivers like the benefits of a graduated tint, as the top part of the lens in which you look out is darkest. The bottom part of the lens is generally lighter and this makes it easier to see the controls within the car.
Safety of the lenses
All sunglasses should carry the CE mark and meet the European Standard BS EN 1836:2005.
A good quality anti-reflection coating is recommended, along with a hard coating to protect the lenses from scratches.
Sunglasses with deep side arms can block side, or peripheral, vision and are not recommended for driving.
Our top tips
- Have a thorough eye examination every two years to find out if you need prescription lenses in your sunglasses.
- Discuss the options for sun and glare protection with your optician.
- Consider a specialist driving lens or tint.
- Be aware that your everyday sunglasses might not be suitable for driving.
- Always keep a spare pair of driving sunglasses in the car so they're ready to put on during road trips.
Remember, the onus is on you to have good vision. If you don't have your vision corrected and protected from the sun, it could invalidate your car insurance if you're involved in a crash.