UV400 Sunglasses Explained

What UV400 means

UV radiation sits in the electromagnetic spectrum from approximately 100 to 400 nanometres (nm). The sun emits UV radiation constantly, but most of it is absorbed by the Earth's ozone layer before it reaches us. The UV that does reach the surface falls into two main categories that concern eye health: UVA and UVB.

UV400 certification means a lens blocks 100% of UV radiation up to 400 nanometres. The "400" is not an arbitrary number — it marks the upper boundary of the UV spectrum, the point at which UV transitions into visible violet light. So a UV400 lens covers the entire range of UV radiation that reaches the Earth's surface.

The standard is defined under EN ISO 12312-1, the European standard for sunglasses that is widely adopted globally. It requires that UV400-certified lenses transmit no more than 1% of UV radiation at 380nm and above. In practice, most quality UV400 lenses block close to 100% across the full UV range.

Other terms you may see that mean the same thing:

• "100% UV protection"
• "UV protection to 400nm"
• "Blocks all UV rays"

All of these are equivalent to UV400 when properly certified.

UVA vs UVB — what's the difference?

UV radiation that reaches the Earth's surface is split into UVA and UVB bands. Understanding both helps explain why UV400 coverage matters.

UVA (315–400nm): Longer wavelength UV. Penetrates deeper into the eye, reaching the lens and retina. Associated with long-term damage including cataracts and age-related macular degeneration (AMD). UVA passes through glass and clouds — it is present even on overcast days and through car windshields. This is the UV that concerns you on a daily basis.

UVB (280–315nm): Shorter wavelength UV. More energetic than UVA. Causes photokeratitis — essentially a sunburn on the cornea — which produces pain, redness, and temporary vision loss. UVB is mostly absorbed by glass and is more intense during peak sun hours. It is also the type of UV that causes most of the damage from welding flash without protection.

Both UVA and UVB are blocked by a properly certified UV400 lens. This is why UV400 is the relevant standard rather than just "UV protection" — it specifies that both bands are covered across the full 400nm range.

The World Health Organisation (WHO) and various ophthalmological bodies have linked chronic UV exposure to:

• Cataracts (clouding of the eye lens)
• Age-related macular degeneration
• Pterygium (tissue growth on the cornea)
• Photokeratitis (short-term UV sunburn of the cornea)
• Increased risk of certain eyelid skin cancers

UV400 vs lens tint — a critical distinction

This is one of the most important things to understand about sunglasses: a dark lens does not mean UV protection.

UV protection comes from a chemical treatment applied to or embedded in the lens material — not from the darkness of the tint. A very dark lens with no UV treatment can actually be more harmful than wearing nothing at all. Here's why: behind a dark lens, your pupils dilate more than they would in bright conditions, allowing more UV radiation to enter the eye — without the UV filter to stop it.

Consider this comparison:

The lesson: always look for the UV400 label, not just a dark tint. Cheap fashion sunglasses with no UV certification may look like proper sunglasses but provide no meaningful eye protection.

UV400 vs lens category

These are two separate standards that measure different things and are often confused.

Lens categories (Cat 0–4) measure Visible Light Transmission (VLT) — how much visible light passes through the lens. Cat 3, for example, blocks 83–92% of visible light. This is the darkness rating.

UV400 measures how much UV radiation is blocked — invisible radiation beyond the visible spectrum. A lens can be Cat 3 (very dark) without being UV400. Equally, a nearly-clear Cat 0 lens can carry UV400 certification.

For sunglasses to be genuinely protective outdoors, you want both:

• Cat 3 for visible light reduction (or Cat 2 for overcast conditions)
• UV400 for UV protection

Neither alone is sufficient. Read our Cat 3 guide for more detail on visible light categories.

How to check if your sunglasses are UV400

Here are practical ways to verify UV protection:

Check the label or packaging: Look for "UV400," "100% UV protection," or "UV protection to 400nm" printed on the frame, lens, or packaging. Reputable brands include this clearly.

Ask the retailer: Any legitimate optical or sunglasses retailer should be able to confirm UV certification. If they can't, treat that as a red flag.

UV meter cards: Inexpensive UV-reactive cards (available from optical supply shops) change colour in UV light. Hold the card in direct sunlight, then shade it with your lens — a UV400 lens should prevent the card from reacting. Note: these are indicative, not laboratory-grade.

Be sceptical of street-market sunglasses: Very cheap sunglasses sold without any documentation or branding are unlikely to carry genuine UV400 certification. This does not mean every inexpensive pair is unsafe — some budget brands do use UV-treated lenses — but verification becomes more important, not less.

Why UV protection matters especially in Singapore

Singapore sits approximately 1.3 degrees north of the equator. The sun's angle is nearly vertical for much of the year, which means UV radiation arrives with minimal atmospheric filtering.

Singapore's UV Index (UVI) regularly reaches 11 or above during peak hours (10am–3pm). The WHO classifies a UVI of 11+ as "Extreme" — the highest category on their scale. For comparison, London rarely exceeds UVI 7 in midsummer.

The National Environment Agency (NEA) publishes daily UV forecasts for Singapore, and "Extreme" readings are common year-round — not just in summer, because Singapore has no meaningful seasons.

What this means practically: UV exposure in Singapore accumulates faster than in most countries. Someone who works or exercises outdoors in Singapore is accumulating far more cumulative UV exposure over a lifetime than an equivalent person in a temperate climate. UV400 sunglasses worn consistently during outdoor activities are one of the most effective and accessible ways to protect eye health over the long term.

See our guide to sunglasses for Singapore weather for full recommendations tailored to the local climate.