|
|||||
 |
|
|
European
Standard EN 1836 specifies how the lenses should perform to permit traffic
lights to be recognized. It does this by defining the ratio between the general
level of light transmission, and the level of transmission for four crucial
colours: red, yellow, green and blue. The ratio must be 80% for red, 80% for
yellow, 60% for green and 40% for blue. This means that the transmission
curve of a lens suitable for driving will usually look similar to that shown in
the diagram above. Such a curve is produced by a brown or orange/yellow lens. AVOIDING
THE BLUES Blue
light makes things look blurred. An explanation for this may be seen the diagram
above, which illustrates how, when green/yellow light is focussed sharply on the
retina, blue light is focussed in front of the retina, and a blurred blue image
results.
The
requirement in European Standard EN 1836 that lenses for driving should retain
some blue transmission, so that traffic lights can be distinguished, means that
lenses suitable for driving are not technically classified as 'blue blockers'.
As blue light is part of the visible spectrum, blocking it completely results in
colour distortion.
Materials
for driving lenses, as for all ophthalmic and sun eyewear, include hard resin,
polycarbonate and glass. An example of a resin lens is the Clarlet Skylet 'Road'
from Zeiss, which is part of a range of colour-contrast lenses with
similarly-shaped transmission curves. It provides 80% absorption. Similarly, 'Thrama
Drive', manufactured by Intercast, is specially developed for improving visual
acuity and drivers' reaction times. As
shown the diagram above, these, and most other contrast-enhancing lenses, not
only reduce blue-light transmission but also frequently have a 'bump' in the
transmission curve at around 550nm wavelength. This wavelength is the one to
which the eye is most sensitive.
With
their exclusive color, Jeep®, JDL lenses provide improved visual perception of
color contrasts and traffic signals. An
example of a polycarbonate lens is the Jeep JDL which combines Sola lens optics,
Jeep branding and L'Amy frames. Some companies make a marketing feature of the
optical qualities of glass, for example,
Serengeti
Eyewear.
Factors
driving our clients choice of lenses for the road should therefore include the
time of day they intend to drive (and therefore the amount of tint permissible),
reduction of blue light, and conformity with EN 1836 - besides looking good. 20/20 03/2001 EYES ON THE ROAD Sun and summer go together like sea and sand. But for Europe's drivers, including holidaymakers on long journeys, sunlight and glare can literally be a killer. Drivers' lenses are to deliver comfortable and stress-free vision - allowing Europe's drivers to keep their eyes on the road. Brian Mc Gee reports. People taking to the roads this summer may be driving in all sorts of conditions - ranging from bright to poor sunlight through to rain, haze and summer storms. Irritating light conditions often accompany driving, an activity which imposes stringent demands on vision and exacts high levels of concentration. Drivers' visual comfort is therefore paramount. "A lot of drivers complain of fatigue and light- sensitivity," says Jean-Pierre Perret of Perret Maitres Opticiens in Geneva, Switzerland. It is difficult to make a direct link between wearing drivers' lenses and improved road safety, given the large number of variables that may be involved in road accidents. But it is reasonable to argue that drivers are more likely to see better if they enjoy the increased visual comfort offered by drivers' lenses. Moreover better, more comfortable vision may mean that drivers are more likely to react quickly in dangerous situations. "You literally see people hiding behind their car's sun visor to shield their eyes from Low or bright light," says Marc Karbaron of Optix Optometrists in London. He compares the danger of this stance to that of holding a mobile phone while driving. "If you are uncomfortable driving then you pose a risk to yourself and to those around you." COMFORT IS KEY "If your vision is comfortable, you are better able to concentrate on driving without being distracted," says Professor Heinz Diepes of Aalen University in Germany. Good lenses for driving, argues the European Sunglass Association, enhance contrast and favour the colour red, making it easier to see brake lights and red traffic signals. Critically, drivers' lenses also reduce glare, which is often mentioned by drivers as a source of visual discomfort. It can be a particular problem on large expanses of open road - which are especially common in mainland Europe. Glare is related to blue light. 'Blue light is very scattered. By reducing it you get less aberration and therefore less glare," explains Marc Karbaron of Optix Optometrists in London. However, European Standard EN 1836 requires that lenses for driving retain some transmission of blue light, so that drivers are still able to distinguish the colour of traffic lights. For this reason, the drivers' lenses available on the market reduce blue light but do not block it completely.
|
Without
sunglasses)
)
)
| Copyright © [2008 [Informoptic CH-1272 Genolier/VD Switzerland ]. All rights reserved |