Understanding the Five Categories of Sunglasses

Understanding the Five Categories of Sunglasses

Sunglasses are not just fashion accessories. They come with different tint levels that absorb varying amounts of light. These tints are divided into five categories, from very light (Category 0) to extremely dark (Category 4).

The Concept of Lens Categories:

Whether prescription or non-prescription, sunglasses are tinted in colors like grey, blue, green, red, or brown, the darkness of the tint is controlled and measured in terms of visible light absorption (ABS%), which ranges from 1% to 100%. This ABS% determines the category of the sunglasses.

Examining the Five Categories of Sunglasses:

The five categories are defined as follows:

• Category 0: ABS% is 0% – 10%, very light tint, suitable for overcast conditions, and can be used day and night.
• Category 1: ABS% is 10% – 20%, light tint, suitable for low sunlight, only for daytime use.
• Category 2: ABS% is 20% – 43%, marginal tint, suitable for moderate sunlight, only for daytime use.
• Category 3: ABS% is 43% – 80%, dark tint, suitable for strong sunlight, only for daytime use.
• Category 4: ABS% is 80% – 92%, very dark tint, suitable for very strong sunlight, not suitable for driving.

Recommended Sunglass Categories for Different Activities:

For recreational activities like driving, walking, and sports, most people prefer category 2 or 3 sunglasses. Category 1 sunglasses, while lightly tinted, are not enough for bright sunny days and are usually used for fashion like Balenciaga sunglasses. Category 4 sunglasses, on the other hand, are meant for high-exposure scenarios like mountaineering and are not legal for driving in some countries.

Detailed Description of Each Sunglass Category:

Category 0 sunglasses have a slight tint and absorb as little as 5% of light. They are often used for prescription glasses.

Category 1 sunglasses have coloration but are too light for everyday use. They offer mild relief on bright days and are popular among people living in sunny locations or those with sensitive eyes.

Category 2 sunglasses balance a dark spectacle lens and a light sunglasses lens. They absorb less than half of the sunlight and can be used on moderately bright or overcast days.

Category 3 sunglasses absorb around two-thirds of visible light. They are suitable for everyday recreational activities like sports, driving, or a day at the beach under a blue sky.

Category 4 sunglasses are the darkest and absorb the most visible light. They are unsuitable for driving due to their darkness but are ideal for extreme exposure scenarios like high-altitude mountaineering.

Decoding the UV400 Label:

The term ‘UV400’ found on sunglasses signifies the level of UV protection offered by the sunglasses. Specifically, ‘UV400’ implies that the sunglasses can block UV light up to the 400-nanometer wavelength, encompassing both UVA and UVB rays. This means they offer nearly 100% effective protection against harmful UV light, blocking out 99-100% of UVA and UVB rays.

The Importance of UV Protection in Sunglasses:

Regardless of the category or darkness of the sunglasses, UV protection is the single most critical factor. Exposure to UV light can lead to severe eye conditions such as cataracts, photokeratitis, macular degeneration, and even blindness. Therefore, always ensure your sunglasses are rated with full UV protection.

The Role of Tint in Sunglasses:

Contrary to popular belief, the darkness of a lens does not correlate with UV protection. The tint on sunglasses only reduces the amount of visible light passing through the lens but does not block UV light. Ironically, a very dark lens without UV filtration could cause your pupils to dilate, allowing more visible and UV light into your eyes, leading to potential eye damage.

Distinguishing Between 100% UV Protection and Polarized Lenses:

While both UV protection and polarized lenses serve to protect your eyes, they are not the same. UV protection is mandatory and blocks harmful UV light. In contrast, polarized lenses are optional and help reduce glare from reflected and overhead sunlight.

Furthermore, while all polarized lenses should be UV protective, they also contain an additional filter called a polarizer. This filter helps block horizontal light, which occurs when light is reflected off surfaces like water, snow, buildings, or cars, causing glare.