What UV400 actually means
Ultraviolet light sits just beyond the violet end of visible light. The part that reaches the ground is divided into UVA, the longer wavelengths up to 400 nanometers, and UVB, the shorter wavelengths below about 315. A lens marked UV400 is rated to block light across that whole band, up to the 400 nanometer boundary where visible light begins.
The protection comes from the lens material and its coatings, not from the tint. Some lens materials block UV on their own; others get a UV-absorbing coating or additive during manufacture. Either way the result is invisible: a UV400 lens can be clear, lightly tinted or very dark, and the UV performance is the same.
Eye care bodies in the United States recommend sunglasses that block UVA and UVB when you are outdoors, and UV400 is the label that states the lens does so. It is the first thing to look for on a sunglass, before shape, tint or brand.
What UV400 does not mean
It is not darkness. Tint controls how much visible light reaches your eye, which is about comfort and glare. A very dark lens without UV protection is the worst combination: your pupils open wider behind the dark lens and let more unfiltered light in. A clear lens with UV400 protects better than a dark lens without it.
It is not polarization. Polarized lenses cut reflected glare from flat surfaces such as water, wet roads and car hoods. That is a separate filter with a separate purpose, and a polarized lens is not automatically UV400, nor the other way round. The guide to polarized vs non polarized sunglasses covers when polarization helps, and what are polarized sunglasses explains the mechanism.
It is not an impact or safety rating. UV400 describes light, not strength. Sport and safety ratings are different standards and are marked differently.
It is not blue light filtering. Blue light is visible light, above 400 nanometers. A UV400 lens may or may not filter it; the label does not say.
UV400 versus "UV protection" and other labels
Sunglasses carry a range of UV wording, and not all of it is equal.
- UV400 states the wavelength ceiling. It is the clearest single label.
- "UVA and UVB protection" or "UV protection" without a figure usually means the same thing but does not state the ceiling. Ask or check the product page for the UV400 figure.
- Category numbers (0 to 4) describe tint darkness, not UV protection. A category 3 lens can be UV400 or not.
- "Blocks UV rays" with no further detail is marketing language. Look for the UV400 label behind it.
How to check a pair you already own
Look for the marking. Many frames print UV400 on the inside of a temple or on a lens sticker when new. If it has worn off, the product page or the box usually states it.
Have it measured. Opticians and many optical stores have a UV meter that reads a lens in seconds and will usually check a pair for free. This is the only reliable test; you cannot judge UV performance by looking at a lens or by how dark it is.
Do not rely on home tests. Shining a UV flashlight through a lens at a fluorescent object gives a rough signal at best, and the "dark lens" assumption is wrong often enough that it is not worth the risk.
How to buy UV400 sunglasses with confidence
- Check the product page states UV400. It should be a stated specification, not implied by the word "sunglasses".
- Then choose tint for the use. Gray keeps colors true, brown lifts contrast, and lighter tints suit low light. The driving sunglasses guide covers tint by situation.
- Add polarization where glare is the problem. Water, snow and wet roads reward a polarized lens; the fishing sunglasses and cycling sunglasses guides go into the trade-offs for each.
- Fit matters for coverage. UV reaches the eye around the edge of a small lens as well as through it. A frame that sits close to the face, or a wrap, covers more of the angles that matter outdoors.
- Keep the lens clean, not scratched. Scratches do not remove UV protection, which sits in the material, but they do scatter light. The cleaning guide covers how to clean without damage.
MUJOSH and UV400
Every MUJOSH sunglass lens is UV400, polarized or not. That applies across the sunglasses range and the WAKE UP sport line, and each product page now states it. Polarization is listed separately: the polarized sunglasses collection gathers the frames whose lenses carry a polarizing filter on top of the UV rating.
Two examples that show the difference. The Numer is a narrow acetate rectangle with polarized UV400 lenses, for drivers and anyone who spends time near water. The Jasmin Straight is a cat eye cut for a lower nose bridge, also polarized and UV400. Both carry the same UV rating; the polarization is the extra.
A photochromic lens blocks ultraviolet in both its clear and dark states; the photochromic lenses guide explains how the darkening works and where it falls short.
UV400 says nothing about lens colour, and lens colour says nothing about UV; the tinted sunglasses guide covers what grey, brown, green, yellow, rose, blue and red lenses each do once the UV block is taken care of.
The bottom line
UV400 is the label that tells you a sunglass lens blocks ultraviolet light across the full UVA and UVB range. It is independent of tint and of polarization, so check for it first and choose the rest for comfort and use. If a product page does not state it, ask before you buy; if you already own a pair and are not sure, have an optician measure it.
If you plan to pay with an FSA or HSA card, the FSA and HSA eligibility guide explains which sunglasses qualify and what the receipt needs to show.
The frame material is a separate decision from the lens; if you are weighing a metal frame, the titanium sunglasses guide covers when titanium is worth the money.
If the question behind your search is screens rather than sun, the do blue light glasses work guide sets out what the trials found.
Full protection is the one thing price should never touch; the affordable sunglasses guide covers what else a pair under $100 should give you.
Protection is the first of six quality checks; the high quality sunglasses guide covers the other five.
Frequently asked questions
What does UV400 mean on sunglasses?
That the lens is rated to block ultraviolet light up to a wavelength of 400 nanometers, which covers the full UVA and UVB range that reaches the ground. It is a statement about UV filtering, not about tint, polarization or impact strength.
Is UV400 good for sunglasses?
Yes. UV400 is the standard to look for, because it states the full UV range is covered. Any sunglass worn outdoors should carry it; tint and polarization are then chosen for comfort and glare.
Are polarized sunglasses the same as UV400?
No. Polarization cuts reflected glare; UV400 blocks ultraviolet light. A lens can be one, both or neither. Look for both labels if you want both benefits.
Do darker lenses block more UV?
No. UV protection comes from the lens material and coating, not the tint. A dark lens without UV protection is worse than a clear lens with it, because the dark tint opens your pupils and lets more unfiltered light in.
How can I check whether my sunglasses are UV400?
Look for the UV400 marking on the temple, the lens sticker, the box or the product page. If none is present, an optician's UV meter reads the lens in seconds and is the only reliable test.
Are MUJOSH sunglasses UV400?
Yes. Every MUJOSH sunglass lens is UV400, whether or not it is polarized, and each product page states it. Polarized frames are listed separately in the polarized sunglasses collection.
