Sunglasses lenses are categorised by darkness of tint. There are five categories in total which transmit measurably different amounts of light through the lenses. These tints range from very light (category 0) to extremely dark (category 4.)
So, are dark sunglasses better?
No. Darker lenses simply transmit less visible light which has no effect on UV protection whatsoever. Darker sun lenses simply just transmit less visible light which can make it more comfortable for you to see. UV is invisible and must be blocked, regardless of lens darkness and their designated lens category.
In this article, you can learn about the 5 sunglasses categories and how they affect your vision when looking through each type of lens.
What are the 5 sun lens categories?
The five sun lens categories are defined by their level of darkness which is affected by the percentage of visible light they transmit. Known as Light Transmission Factor (LTF) these five categories range from 0,1,2,3, and 4 with decreasing levels of transmission.
Category 0 and 1 lenses are very light in colour as they transmit a large amount of visible light. Category 2 and 3 lenses are the most common darkness. Category 4 lenses are very dark in colour, transmitting very little visible light.
See the table below as a guide;
|
Category |
0 |
1 |
2 |
3 |
4 |
|
LTF |
80-100% |
43-80% |
18-43% |
8-18% |
3-8% |
|
Colour tone |
Very light |
Light |
Medium |
Dark |
Very dark |
|
Sun use |
Overcast |
Low |
Moderate |
Strong |
Very strong |
|
Driving suitability |
Day & night |
Day only |
Day only |
Day only |
Never |
How do I know what category my sunglasses are?
The easiest way to know the category of your sun lenses is checking with the merchant where you bought them from. Most 'dark' sun lenses are usually category 3. However, if want to be certain, you can have their transmission percentage measured (LTF) by an optician who can use a device called a photometer.
What is the best category for sunglasses?
Depending on your application, most recreational sunglasses use category 2 or 3 lenses for driving, outdoor activities such as hiking or water sports like fishing.
Category 1 lenses are very lightly tinted, with little to no darkening effect. This is usually insufficient for bright sunny days and are typically just used for fashion purposes or light sensitive eye conditions.
Category 4 lenses are considered specialist for high-exposure scenarios like mountaineering and are in fact illegal for driving in the UK.
For more details, check out the following descriptions and applications of the 5 lens categories in the list below.
What are category 0 sunglasses?
Category 0 lenses have little to no tint which barely reduces the darkness of the lens. With as much as 90% of the light being transmitted, category 0 lenses are vaguely tinted and are used for prescription spectacles.
What are category 1 sunglasses?
Category 1 lenses have a more obvious colouration from tinting, but would still be far too light for use as everyday sunglasses. Category 1 lenses are basically a coloured spectacle lens which offer mild relief on bright days. A popular choice for people who live in very sunny locations or have sensitive eyes.
What are category 2 sunglasses?
Category 2 lenses are the halfway point between dark spectacle lenses and a light sunglasses lenses. Their colouration is more prominent and transmits around half of visible light. Category 2 lenses could be used as sunglasses on moderately bright or overcast days.
What are category 3 sunglasses?
Category 3 lenses transmit around one third of visible light which makes them suitable as everyday recreational sunglasses for activities such as sport, driving or a blue-sky day on the beach.
What are category 4 sunglasses?
These are the darkest sun lenses. Because they transmit very little visible light, they’re illegal to wear for driving. Generally, these lenses are only suitable for extreme exposure scenarios such as high-altitude mountaineering. Not your everyday sunglasses lens.
What are category 5 sunglasses?
Category 5 lenses are considered the same as category 4 lenses if you start from 1 instead of 0. These lenses only transmit 3-8% of visible light and are extremely dark to look through. They are designed for high exposure excursions such as mountaineering.
What does UV400 mean on sunglasses?
UV400 or UV40 sunglasses have lenses which block 99-100% of UVA and UVB (ultraviolet) sun light. This means they properly protect your eyes from the most damaging frequencies up to 400 nanometres, hence the name.
You must remember that regardless of sunglasses categories, protection against ultraviolet light is the single most crucial factor of any pair of sunglasses.
Truth be told, the darkness of a lens has nothing to do with UV protection. Tint only reduces the amount of visible light which can pass through a lens and doesn't block any UV.
Ironically (and dangerously) a very dark lens without UV filtration would make your pupils dilate to let more visible and UV light-in. This would seriously damage your eyes and could lead to significant or permanent damage such as cataracts, photokeratitis, macular degeneration or even blindness.
Always check that your sunglasses are rated with full UV protection.
At Banton Frameworks, all our sunglasses are 100% UV protective in compliance with European standards.
Visible light can pass through a UV400 sun lens | UVA & UVB cannot pass through | UVC is absorbed by the atmosphere
Is UV the same as polarised?
UV protection is not the same as polarised lenses. Protection from ultraviolet light is a mandatory function whereas polarisation is an optional upgrade to reduce glare from reflected sunlight.
Polarised lenses must always be UV protective, but they also contain an additional filter called a polariser. This filter is a chemical film which is built into the layers of the lens construction.
Upon the filter are microscopic rows of molecules which are vertically aligned in relation to your eyes. This creates a filter which blocks horizontally orientated light.
But what is horizontal light?
Horizontal light occurs when it’s reflected off molecules in the air or when it bounces off large shiny surfaces such as water, snow, buildings or cars. These flat surfaces re-orientate and condense the light into what is called glare.
Glare is uncomfortable to look towards and interferes with your vision. It can affect your perception of colour and contrast as well as putting more strain on your eyes.
With their in-built filter, polarised sunglasses can block most of this distracting glare from entering your lenses; making them more consistent and smoother than regular sun lenses.
This is why they're such a popular choice for sunglasses for driving or if you play outdoor sports.
Does Category 3 mean Polarised?
Lens category simply denotes the darkness of sunglasses lenses and does not mean they are polarised. Category 3 sun lenses are the most common darkness of sun lenses, fitted to most recreational sunglasses as they provide sufficient visual comfort for most applications.
Polarisation is a separate aspect from lens categories, which means the sun lenses contain a polariser within. This additional feature is what differentiates polarised lenses from regular (non-polarised) lenses and helps diminish glare.
A category 3 lens can be either polarised or non-polarised, but must always be rated as UV400 to give you proper protection from the sun.
How are lenses darkened?
Sun lenses are made by darkening a prescription or non-prescription lens with a tint dye such as grey, green or brown.
Depending on the darkness required, their light transmission factor (LTF) is controlled by the duration of which they're immersed in the tint. This occurs in a heated liquid bath of dye which penetrates the uncut lens (seen below).
LTF denotes the amount of light transmitted by sun lenses which can be anything between 1% or 100%. It’s this percentage that informs the five sunglasses categories.
Summary
- Lenses are categorised into 5 types, ranging from light to dark.
- Tint darkness is measured as a percentage called light transmission factor or LTF for short.
- Sunglasses must be 99-100% protective against ultraviolet light and state or be accompanied with the UV40 or UV400 rating in compliance with European law.
- Lens darkness has no relevance towards UV protection as is merely a personal preference based on how you use your sunglasses.
- Category 4 lenses are illegal for use whilst driving in the UK and are best avoided unless you require them for extreme exposure scenarios.
- Polarised lenses are a secondary option and have no effect on UV protection. They are simply used to reduce reflected glare.
Hopefully you found this article helpful. Please check out our other sunglasses blogs for more useful advice. Thanks for stopping by.