Sunglasses, Polarised and Photochromic Lenses, Tints and Night-Driving Glasses: A Practical Guide
Last updated: November 2026
RPC Rounds for Optometrists · B.Optom study guide
Patients ask the optician which sunglasses to buy far more often than they ask the doctor. This page explains what sunglasses must do, the filter categories, tint colours, polarised and photochromic lenses, the truth about night-driving and blue-cut glasses, and which lens to recommend for each need.
What good sunglasses must do
- Block ultraviolet (UV) light. Look for "UV400" or "100% UV protection", meaning UVA and UVB up to 400 nm are blocked. Darkness does not equal UV protection: a dark lens without UV filtering dilates the pupil and lets more UV in.
- Reduce brightness to a comfortable level: this is the filter category (below).
- Reduce glare from water, roads and snow: this is what polarisation does.
- Not distort colours or traffic signals, especially for driving.
- Be impact resistant for children and sport (polycarbonate or Trivex).
Filter categories (ISO 12312-1)
| Category | Light let through | Use | Driving? |
|---|---|---|---|
| 0 | 80–100% | Clear or very light tint; indoors, cloudy days, fashion | Yes, day and night |
| 1 | 43–80% | Light tint; overcast days | Yes in daytime; not at night |
| 2 | 18–43% | Medium; ordinary sunshine | Yes in daytime |
| 3 | 8–18% | Dark; bright sun, beach, most sunglasses | Yes in daytime |
| 4 | 3–8% | Very dark; glaciers, high mountains, desert | No, never |
Lenses for driving at dusk or at night must let through at least 75% of light. In practice that means a clear lens with an anti-reflection coating.
Tint colours
| Colour | Effect | Good for | Avoid for |
|---|---|---|---|
| Grey | Reduces brightness evenly; true colours | General use, driving, bright sun | — |
| Brown, amber, copper | Blocks some blue light; increases contrast | Driving, golf, cricket, fishing, hazy days | Work needing exact colour judgement |
| Green (G-15 type) | Near-natural colours with good contrast | General use, outdoor sports | — |
| Yellow or orange | Brightens and sharpens contrast in dull light | Shooting, cycling in haze, indoor sports | Bright sun; night driving |
| Rose or red | Raises contrast against green and blue backgrounds | Skiing in flat light, some sports | Driving (alters traffic-light colours) |
| Blue or violet | Mostly cosmetic | Fashion | Driving |
| Gradient (dark top, light bottom) | Shades the sky while keeping the dashboard and reading clear | Driving, fashion, progressive sunglasses | — |
| Mirror coating | Reflects extra light; hides the eyes | Water, snow, high glare | —; add a back-surface AR coating to stop reflections from behind |
Some tints are medical: rose (FL-41-type) tints can help migraine and light sensitivity, and amber-red cut-off filters help some patients with retinitis pigmentosa, albinism, aniridia or cone dystrophy. Refer these patients for assessment rather than choosing for them.
Polarised lenses
Light reflected from flat, horizontal surfaces such as water, wet roads and car bonnets is partly polarised horizontally. A polarised lens has a filter with a vertical transmission axis that blocks this horizontally polarised glare.
| Advantages | Limitations |
|---|---|
| Cuts reflected glare from water, roads and snow | Phone, car dashboard, ATM and some instrument screens may look dark at certain angles |
| More comfortable, clearer view when driving and boating | Can make icy patches and some reflections that warn of hazards harder to see |
| Fishermen can see into the water | Stress patterns may appear in toughened car windows |
| Available in prescription single vision and progressive | Pilots are usually advised not to use them (cockpit displays, reduced view of reflections from other aircraft) |
Remember: polarisation is about glare, not UV. A polarised lens still needs a UV400 filter, though almost all good ones have it. Quick test at the counter: hold two polarised lenses in front of each other and rotate one by 90°; the view should go dark. Or look at a phone screen and tilt your head.
Photochromic (light-reactive) lenses
- Darken in UV light outdoors and clear indoors, so one pair works as both spectacles and sunglasses.
- Darken poorly in a car, because windscreens block most UV. Some newer versions also respond to visible light and darken partly behind a windscreen; explain this before ordering.
- Get darker in cold weather and lighter in hot weather; in Indian summers they may not become as dark as a category 3 sunglass.
- Darken in about a minute but take several minutes to clear fully; patients may find them too dark when they first walk indoors.
- Performance falls over the years. If one lens is replaced, replace both so they match.
- Available in grey, brown and other colours, in most materials and in progressives; polarised photochromic lenses exist for drivers.
Night-driving and "night vision" glasses
Yellow "night-driving" glasses are widely sold but do not help. Any tint reduces the light reaching the eye at night. In a driving-simulator study, yellow lenses did not improve pedestrian detection and did not reduce the effect of headlight glare.
What does help a patient who struggles to drive at night:
- An up-to-date prescription, including small amounts of myopia or astigmatism that do not matter in daylight.
- Clear lenses with a good anti-reflection coating, kept clean.
- A clean windscreen and correctly aimed headlights.
- An eye examination for cataract, dry eye and other causes of glare. See driving eyesight rules in India.
Blue-cut lenses
A Cochrane review found that blue-light filtering spectacle lenses probably make no difference to eye strain from screens in the short term, and that there is no good evidence that they protect the macula. Offer them as a choice if a patient wants them, without claiming medical benefits. For screen strain, check the refraction, binocular vision and dry eye, and advise regular breaks. "Blue cut" and "blue block" are trade names, not technical terms, and shops use them for the same thing. What differs is how the lens filters blue light: a reflective coating (the lens looks clear but shows a blue or violet reflection), a blue-absorbing lens material (a faint yellow tint, less reflection), or amber or orange "blue-blocker" glasses that remove most blue light and change colours, sold for evening use and sleep. Ask the supplier how much light is blocked between about 400 and 455 nm instead of relying on the name.
What to recommend for each need
| Need | Recommendation |
|---|---|
| Daytime driving | Grey or brown, category 2–3, polarised; check that the dashboard screen is readable |
| Driving at night | Clear lens with AR coating; no tint, no yellow glasses |
| Beach, boating, fishing | Polarised, category 3; amber or copper for fishing |
| Snow, high mountains | Category 4 wraparound with side protection (not for driving); category 3 for normal skiing |
| Cricket, tennis, golf, cycling | Polycarbonate or Trivex, wrap frame, amber or brown for contrast |
| Children | UV400, polycarbonate, category 2–3, a flexible frame or strap |
| After cataract surgery, dilated pupils, light sensitivity | UV400 wraparound, category 2–3 |
| Office and computer | Clear lens with AR coating; tints and blue-cut are optional |
| Pilots | Non-polarised, grey, category 2–3 |
| Albinism, aniridia, retinitis pigmentosa | Refer for filter assessment; wraparound frames with side shields |
| Migraine and photophobia | Discuss rose (FL-41-type) tints after an eye examination |
Ordering prescription sunglasses: checklist
Before you send the order
- Check the prescription range for the chosen lens: polarised and wrap lenses are not available in every power and index.
- In high-wrap sports frames (6 or 8 base), lenses need wrap and tilt compensation; order a freeform single-vision design and give the wrap and tilt measurements. Very high powers may not be possible.
- For progressive sunglasses, measure the fitting height in the actual sunglass frame; sunglass frames often sit lower and further from the eye.
- Write the tint colour, category (or percentage), gradient direction, mirror colour and back-surface AR coating.
- Confirm UV400 on the lens specification.
- Show the patient a polarised demo card and a phone screen, and explain the screen effect.
- For photochromics, explain the car-windscreen and temperature effects before ordering.
- Never sell a category 4 or a tinted lens for night driving.
Practical pearls
- Ask every sunglass buyer one question: "Where will you wear them most?" Driving, water, sport and snow each need a different lens.
- Show the patient a phone screen through a polarised lens before ordering, especially drivers with screen dashboards.
- Tell photochromic buyers that the lenses will not darken much in the car; offer a separate polarised pair for driving.
Where students slip
- Assuming a darker lens gives more UV protection.
- Selling yellow "night vision" glasses for night driving.
- Recommending category 4 lenses for driving.
Test yourself: flip cards
Quick quiz
Related: Spectacle Lens Types Compared: Single Vision, Bifocal, Trifocal, Progressive and Office Lenses, With an Order Checklist, Spectacle Lens Materials and Coatings: CR-39, Polycarbonate, Trivex, High Index, Abbe Value and Blue-Cut, Occupational and Sports Optometry: Visual Standards, Protective Eyewear and Screen Use, Eyesight Rules for a Driving Licence in India: Glasses, Colour Vision and One Eye, Eyeglass Lens Coatings Guide Ahmedabad. Back to the optometry curriculum.
Key sources
- ISO 12312-1:2022. Eye and face protection: Sunglasses and related eyewear. Part 1: Sunglasses for general use
- Hwang AD, Tuccar-Burak M, Peli E. Comparison of pedestrian detection with and without yellow-lens glasses during simulated night driving with and without headlight glare. JAMA Ophthalmol. 2019
- Singh S, et al. Blue-light filtering spectacle lenses for visual performance, sleep and macular health in adults. Cochrane Database Syst Rev. 2023
- American Academy of Ophthalmology. Recommended types of sunglasses (EyeSmart)
- Jalie M. Ophthalmic Lenses and Dispensing. 3rd ed. Butterworth-Heinemann; 2008
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