Cat 0 lenses are either clear or have a very light tint, they are used for safety glasses or spectacles where you need to see clearly what you are doing.
Cat 1 lenses are for casual use, used as a comfort filter in cosmetic and fashion eyewear.
Cat 2 lenses are the most common category to be found in sunglasses, for general use they provide good protection from visible light and from UV rays. This lens will have a tint which allows through less light than category 1 but more light than category 3
General Purpose, watching and taking part in sport
Cat 3 - Provide extra protection from both visible and UV light. These lenses will usually only allow less than 20% of visible light to penetrate the lens. This means that they will block out 80%+ of light.
Open mountain ranges
Cat 4 - Provide a high level of protection from visible and UV light. These lenses are not to be worn when driving as they are too dark. These lenses will allow less than 10% of light to transmit through the lens. They are to be used for specific situations only - not for a pair of everyday sunglasses.
High altitude trekking and mountaineering.
Clearly there is not a single lens to suit every set of conditions, this is where sunglasses with a range of lenses come in, or photochromic lenses that adapt to the light conditions. READ MORE>
Ultraviolet Light (UV) Protection - Overexposure to ultraviolet light is thought to be a cause of cataracts, retinal damage and other eye problems, so protection from UV rays is an essential function of sunglasses, all our sunglasses offer 100% UV protection, no UV light will pass through the lens.
Visible Light Transmission (VLT) - This is the measure of how much light your sunglass lens lets through to your eye and can be expressed as a percentage, therefore a VLT of 1% means very dark glasses indeed, and a VLT of 100% means all the light is getting through and the lens is therefore a 'clear lens'.
Rather than quote a percentage for each lens they are categorised as follows:
Lens Categories - The most common lens colour (tint) is Brown, this is because these lenses (along with Grey and Green) are 'colour neutral', that is they cut down on overall brightness without distorting colours thereby accentuating relief.