Just about everybody understands the concept of UV protection and sunglasses. Scientists have been telling us for years how bad ultraviolet light is for the eyes, so we are all pretty familiar with the idea of wearing sunglasses to prevent UV damage. But what about the VLT? Do you know what the acronym means? Moreover, do you know the difference between UV and VLT protection?
This post will examine that difference along with explaining why it is important. Next time you are in the market for a new pair of sunglasses, pay attention to both ratings. They are equally important for keeping the eyes healthy.
You Can’t See Ultraviolet Rays
We will start with UV protection. The thing about UV rays is that you cannot see them with the naked eye. UV rays are part of the light spectrum that are only visible with specialized equipment. But just because you can see them doesn’t mean you’re safe when exposed to them. You are not.
Ultraviolet rays exist on the electromagnetic spectrum at wavelengths ranging from 10 to 400 nm. This is important to know because it will help you better understand UV ratings. A UV rating of 400 tells you that a pair of sunglasses blocks any and all UV rays. A pair with a rating of 300 only blocks wavelengths up to 300 nm.
Olympic Eyewear, a Salt Lake City company that specializes in wholesale sunglasses, says that just about every reputable manufacturer these days makes lenses with a minimum UV rating of 300. Most go right up to UV 400.
You Can See Visible Light
Moving on, the ‘VLT’ acronym stands for ‘visible light transmission’. Visible light is light you can see with the naked eye. It is the light you see when you are staring at the sun or looking at a lamp. And though it doesn’t do the same kind of damage that UV rays do, visible light can harm the eyes nonetheless.
Protecting against harm is a matter of filtering out excess amounts of visible light. Now, here’s where this gets interesting. Because UV rays cannot be seen by the human eye, UV protection has nothing to do with tint. A pair of sunglasses with absolutely no tint can still offer full UV protection.
Visible light is another story. You filter out visible light by using tint to block it. The darker the tint, the more visible light protection you are getting. Eyewear manufacturers rate VLT protection using something they call the ‘protection index’.
Understanding VLT Ratings
Sunglasses are rated from 0 to 4 in terms of their VLT protection. The higher the rating, the more protection. However, there is a bit more to it. Olympic Eyewear explains that a pair of sunglasses with a VLT rating of 0 allows between 80 and 100% of all visible light to pass through. This would be a nearly transparent pair of glasses with nothing more than a very slight tint.
Here are the other four ratings:
- 1 – 43 to 80% (light tint)
- 2 – 18 to 43% (medium tint)
- 3 – 8 to 18% (dark tint)
- 4 – 3 to 18% (very dark tint).
It should be obvious that blocking all visible light would result in you not being able to see through the lenses. That said, even 3% is still quite low. It is probably a safe bet that anything lower than 18% is not appropriate for everyday use.
Now you know the difference between UV and VLT ratings. As a more educated consumer, you can now make more educated purchase decisions.