Sunglasses - a shady business?

The sky's blue, sun is shining and the snow, fog and rain are a distant memory. It's time to get the top down, the shades on and celebrate the great British summer with some open-air motoring. But hold on a minute - those shades might make you look cooler than an ice box, but are they OK for driving? Are sunglasses a boon or burden for the safe driver?

Tim Shallcross, IAM RoadSmart's head of technical policy and advice, has put together a set of tips for Sunglasses Day (today – 27 June) outlining key information that you should be aware of.

Did you know about the EU standards for sunglasses?

As a matter of fact, there is an EU standard for sunglasses, ensuring the frames are reasonably strong and sweat resistant and the lenses are shatterproof, scratch resistant and give good protection against harmful ultra-violet light. 

Any which show the CE mark (and any sold in the EU should have it) should come up to the standards, but they are also graded into five categories - 0 to 4 - to show how dark the tint is, or more specifically, how much visible light they let through.

What categories of sunglasses are there?

Category 0 specs allow 80% to 100% of visible light through and are fine for driving at any time. Categories 1, 2 and 3 are progressively darker tints, shielding against brighter levels of sunshine, and while they are all fine for daylight driving, none of them should be worn if you're driving at night. The darkest is category 4, which lets just 3% to 8% of the light through. These are very dark, like ski goggles. They are so dark that they should not be used for driving at any time, and category 4 sunglasses must be labelled as unsuitable for driving.

Category	Description	Use	Driving	Symbol
0	Light Tint	Indoors or Cloudy Day	Any time
1	Light tint	Moderate Sun	Day only, not for night driving
2	General Purpose Sunglasses	Medium Sun	Day only, not for night driving
3	General Purpose Sunglasses	Bright Sun	Day only, not for night driving
4	Very dark	Very Bright Sun/High Glare	Not for driving at any time

 

Where can I find this information?

Seems simple enough. Sunglasses on sale in shops such as chemists or opticians do have the label and are marked with the category - normally on the arm. However, online shoppers beware; a look through several shopping websites revealed that very few sellers display the tint category or any symbol, so you have no way of telling whether the glasses are suitable for driving until they arrive. A few are advertised as category 4 and suggested as being good for cyclists, although the official standard states they are "not suitable for driving and road use", and common sense would say that if they're too dark for driving, they're too dark for cycling. 

Photochromic glasses aren't marked but they should be fine for most cars because they respond to ultraviolet light to darken. Car windows block UV light, so the glasses will stay more or less clear. Watch out if you drive a convertible though, because once the roof's down the glasses will darken, but at their darkest they still allow about 20% of light through, putting them around category 2 or 3. Just be aware that they will stay dark for quite a while if you drive into a tunnel or underpass or a long stretch of shadows.

So, while the sun stays shining, check the tint number before you drive and make sure your shades keep you safe as well as cool.