Photochromic & sun · Guide
How to Choose Prescription Sunglasses: Tint, UV and Frame Shape
Choosing prescription sunglasses comes down to four questions: how dark the lens should be, whether dark means protected from UV, which tint colour to pick, and whether your prescription suits the frame you like. This guide answers each one so you can decide before you pick a frame.
Pick the darkness for where you will wear them, not for how they look in the shop. Check that the lens filters UV, since a dark lens and a UV-blocking lens are not the same thing. Choose grey if you want colours to look normal, brown if you want a little more contrast. If your prescription is strong, a flatter frame usually gives clearer vision than a deeply curved sports wrap.
TL;DR
- Sunglass lenses fall into five darkness categories, 0 to 4. Category 4 lets through only 3–8% of light and is not meant for driving.
- How dark a lens looks tells you nothing about UV. Look for UV400 or a stated UV filter. Every tinted lens we fit filters UV.
- Grey and green keep colours close to normal; brown shifts colours slightly but raises contrast.
- Strongly curved wrap frames suit mild prescriptions best. One US prescription lab puts the comfortable range at about −4.00 to +3.00.
- At Manh Long Optical, polarised lenses are sold without a prescription only, so a tinted lens with anti-reflective coating on the back is the usual alternative.
- 1,850,000₫
- Tinted prescription sunglasses, finished pair including frame
- From 1,550,000₫
- Photochromic pair that clears indoors, frame included
- 3–8%
- Light a category 4 lens lets through (not for driving)
- Non-Rx only
- How polarised lenses are sold at this shop
Prices are from our prescription sunglasses page and vary with prescription strength, lens index and coating. The category figures come from the European sunglass standard, as summarised on Wikipedia.
In this article
How dark should the lens be?
Darkness is measured by how much visible light gets through the lens. The European standard sorts sunglass lenses into five categories by that number. The scale is useful because a lens that feels right under the shop lights can be too dark on a grey afternoon, or not dark enough at midday.
Swipe the table sideways to see all columns →
| Category | Light let through | Typical use |
|---|---|---|
| 0 | 80–100% | Indoors or overcast; a very light tint |
| 1 | 43–80% | Low sun |
| 2 | 18–43% | Medium sun |
| 3 | 8–18% | Strong, bright sun |
| 4 | 3–8% | Very intense light; not for driving or use on the road |
Source: the EN 1836:2005 categories as listed in the Wikipedia article on sunglasses.
If you ride or drive, the category 4 limit matters, because the standard marks those lenses as unsuitable for the road. For daytime use in the city, categories 2 and 3 cover the medium and strong sun conditions in the table.
At the counter we keep tint sample discs. Take one to the doorway and look at the street through it before you decide. Shop lighting flatters every tint.
Is a darker lens more protective?
No. Darkness and UV filtering are two separate properties of a lens. A dark tint cuts brightness. UV filtering blocks ultraviolet light, which you cannot see. A lens can be very dark and still let UV through.
Behind a dark lens your pupils open wider. If that lens does not block UV, the wider pupil lets more of it in, which is the opposite of what you want from sunglasses.
What to look for is a lens labelled UV400, which means it blocks light up to 400 nm and covers both UVA and UVB. The Wikipedia article on sunglasses gives the usual recommendation as blocking 99% or more of UVA and UVB. Every tinted lens we fit filters UV. A clear lens can filter UV too, which is how ZEISS UVProtect clear lenses work, so UV protection is not something only sunglasses give you.
For how UV protection differs from the blue-light filters sold for screen use, see blue-light filtering vs UV protection.
Grey, brown, green or gradient?
Tint colour changes how the world looks, not how well you are protected. Pick it for comfort and for what you do outdoors.
Swipe the table sideways to see all columns →
| Tint | Effect on what you see | Suits |
|---|---|---|
| Grey | Colours stay close to normal | A general-purpose first pair |
| Green | Also neutral; colours stay fairly true | People who find grey too flat |
| Brown | Slightly warmer colours, more contrast | Hazy days |
| Gradient | Dark at the top, lighter at the bottom | Reading a phone, menu or dashboard through the lower part |
Depth of tint usually matters more for comfort than colour. A category 3 grey and a category 3 brown feel closer to each other than a category 2 and a category 3 of the same colour.
Does your prescription suit a curved frame?
Ask this before you fall for a frame. Many sunglass frames curve around the face. A prescription lens has to be ground into that curve, and the stronger the prescription, the harder it becomes to keep the edges of the lens sharp.
One US prescription safety lab gives these working limits for wrap frames with a base curve of 6 to 8:
- Comfortable: about −4.00 to +3.00
- Possible but difficult: up to about −6.00 to +4.00
- Cylinder (astigmatism) above about 2.00 makes adapting to a wrap lens much harder
Those numbers come from one lab, so treat them as a guide rather than a hard rule. The practical point holds: with a strong prescription, a flatter frame with a moderate lens size usually gives clearer vision and thinner edges than a deep wrap. If your lenses are already thick, the lens index guide explains how a higher index keeps them slimmer.
At Manh Long Optical, short-sighted prescriptions up to about −5.00 work fine in a curved sunglass frame. If you are −5.00 or stronger, or also have astigmatism or long-sightedness, bring your prescription to the counter so we can check the specific frame before you decide. Checking first is quicker than changing frames after the lenses are cut.
Photochromic in Hanoi heat and in the car
Photochromic lenses are the other way to wear your prescription in the sun: one pair that is clear indoors and darkens outside. Two things about them surprise people.
First, heat. The chemistry that darkens the lens works less strongly when it is hot, so on a hot day the lens does not get as dark as it would in cool weather. It darkens within about a minute in sunlight, and it does not clear instantly when you walk inside; how long it takes depends on the brand and the temperature.
Second, cars. Photochromic lenses react to UV, and a laminated windscreen blocks most UV. Behind the windscreen the lens stays close to clear even in bright sun. If you drive a lot in daylight, a dedicated tinted pair works better.
For a side-by-side look at both lens types, read photochromic vs polarized lenses. For what the Essilor range costs, see Essilor Transitions prices.
Why not polarised with a prescription?
Polarised lenses block light reflected flat off wet roads and water, which is the glare that makes a road surface look white at midday. That is a real benefit for driving and for time near water.
They also have side effects worth knowing. Phone screens, car displays and other LCD screens can look dark or patchy through a polarised lens, and some car windows show coloured patterns.
At Manh Long Optical we sell polarised lenses without a prescription only. If you need correction and want to cut glare, the usual option here is a dark tint with anti-reflective coating on the back surface of the lens, which cuts the reflections that bounce off the inside of the lens into your eye.
Which setup fits you
- If you spend long stretches outdoors and want proper sunglassesA tinted prescription pair, category 2 or 3
- If you go in and out of buildings all day and hate swapping glassesPhotochromic lenses
- If you drive a lot in daylightA tinted pair; photochromic stays light behind the windscreen
- If your prescription is strong or has high astigmatismA flatter frame rather than a deep wrap
- If glare off water is the main problemNon-prescription polarised over contact lenses, or a dark tint with back-surface anti-reflective coating
FAQ
Can I get sunglasses with a strong prescription?
Usually yes. At Manh Long Optical, short-sighted prescriptions up to about −5.00 work fine in a curved sunglass frame. Stronger prescriptions do better in flatter frames with a moderate lens size, and a higher-index lens keeps the edges thinner.
Which tint category works for riding a motorbike in the city?
Categories 2 and 3 cover medium to strong daytime sun. Category 4 is marked as not for road use in the European standard.
Do darker sunglasses block more UV?
No. UV filtering is separate from how dark the lens looks. Check for UV400 or a stated UV filter rather than judging by colour.
Will photochromic lenses replace sunglasses in Hanoi's summer?
Partly. They darken outdoors, but less in hot weather and hardly at all behind a car windscreen, so people who drive or spend long hours outside often keep a separate tinted pair.
How much are prescription sunglasses at Manh Long Optical?
Tinted prescription sunglasses are 1,850,000₫ for the finished pair, frame included. Photochromic pairs start at 1,550,000₫. The final price depends on your prescription, lens index and coating.
One thing to remember
Choose the darkness for where you will wear the lens, check UV separately, and let your prescription decide how curved the frame can be.
A note on health: Sunglasses reduce brightness and, with a UV filter, block ultraviolet light. They do not treat any eye condition. If something about your vision worries you, see an eye doctor. Prices can change; ask in store before ordering.
Sources
- ReferenceWikipedia: Sunglasses. Lens categories 0 to 4, UV400, tint colours, ISO 12312-1 and ANSI Z80.3.
- ReferenceWikipedia: Photochromic lens. Temperature effect and darkening and clearing times.
- ReferenceWikipedia: Polarized glasses. Glare reduction and the effect on LCD screens.
- Prescription labRx Safety: Prescription limits and lens curvature in wrap frames. Working prescription ranges for 6 to 8 base frames.
- Prescription labRx Safety: Why photochromic lenses don't work well in the car. Windscreens block most UV.
- Business infoManh Long Optical: Prescription sunglasses in Hanoi. Prices, turnaround and the polarised limit.