by Jamie Bartlett December 15, 2019 5 min read

Sunglasses are just sunglasses, right?

Nope.

Besides style, material and shape, their lenses are unquestionably the most important element. But what are the sunglasses categories and why are they so important?

 

Sunglasses lenses are categorised by darkness of tint. There are five categories in total which transmit measurably different amounts of light through the lens. These tints range from very light (category 0) to extremely dark (category 4.)

 

In this article, you can learn about the 5 sunglasses categories and how they affect the way you see when looking through each type of lens.

 

5 sunglasses lenses with different levels of tint darkness

 

What are lens categories?

Sun lenses are made by darkening a prescription or non-prescription lens with a tint colour such as grey, blue, green, red or brown.

Depending on the severity of the tint, their darkness can also be controlled which is measured as a percentage called visible light transmission or VLT% for short.

VLT% denotes the amount of light that can pass through a sun lens which can be anything between 1% or 100%. It’s this percentage that informs the five sunglasses categories.

 

Category

0

1

2

3

4

VLT%

80% - 100%

43% - 80%

18% - 43%

8% - 18%

3% – 8%

Tint

Very light

Light

Marginal

Dark

Very dark

Sun use

Overcast

Low

Moderate

Strong

Very strong

Driving suitability

Day & night

Day only

Day only

Day only

Never


 

Which lens category is right for me?

To give you a better idea of how these lens categories affect your vision, check out the following descriptions and applications in sequence of their category.

Remember, lens tinting can be applied to prescription or plano lenses in order to make them suitable for sun use.

 

What are category 0 sunglasses?

These 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?

These 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?

These lenses are the halfway point between a very dark spectacle lens and a light sunglasses lens. Their colouration is prominent and transmits less than half of sunlight through the lens. Category 2 lenses could be used as sunglasses on moderately bright or overcast days.

 

What are category 3 sunglasses?

Of all the sunglasses categories, these lenses are the most common. Category 3 lenses transmit around a third of visible light which makes them suitable as everyday sunglasses for activities such as sport, driving or a blue-sky day on the beach. Banton Frameworks sunglasses are category 3.

 

What are category 4 sunglasses?

These are the darkest sun lenses you can get. Because they transmit very little 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 transmit less than 8% of visible light and are extremely dark to look through. They are designed for high exposure excursions, usually with side shields for the prevention of snow blindness for mountaineers.

 

 

Strong sunlight bursting through clouds on a sunny day

 

What does uv400 mean on sunglasses?

Ultraviolet light comprises of three divisions called UVA, UVB and UVC which range in frequency up to 400 nanometres.

UV40 or UV400 sunglasses are protective against these UV light-divisons to prevent sun-damage to your eyes.

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.

 

Illustrating how ultraviolet light is blocked by UV400 sunglasses

Visible light can pass through a UV400 sun lens | UVA & UVB cannot pass through | UVC is absorbed by the atmosphere

 

Is 100% UV protection same as polarised?

UV protection is not the same as polarised lenses.

Protection from ultraviolet light is mandatory whereas polarisers are an optional filter which helps to reduce glare from reflected and overhead sunlight.

A little more detail perhaps?

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 tiny rows of molecules which create a directional “grain” sort of like prison bars which are vertically aligned to your eyes. This creates a filter which can block-out most horizontally orientated light.

But what is horizontal light? I hear you ask.

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. The flat surface re-orientates and condenses the light into what we call glare.

It’s painful to look into and boy does it interfere with your vision. Especially when you’re trying to drive your car, play sport or just enjoy the sun!

Because of their in-built filter, polarised sunglasses can block most of this distracting glare from entering your lenses. This makes them more consistent and smoother than regular sun lenses.

A popular choice as sunglasses for driving or if you play a lot of sport.

 

Illustration showing how polarised sunglasses reduce horizontally polarised light

 

Summary

  • Lenses are categorised into 5 types, ranging from light to dark.
  • Tint darkness is measured as a percentage called visible light transmission or VLT% 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 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.

 

grey square polarised sunglasses

 

 

Jamie Bartlett
Jamie Bartlett

Co-founder of Banton Frameworks.



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