Prescription lenses guide
Photochromic Lenses in Kenya: How They Work, What They Protect Against and Where They Fall Short
Photochromic lenses are prescription lenses that darken outdoors and clear again indoors, so one pair can often replace switching between glasses and prescription sunglasses. This guide explains how they work, what "100% UV protection" really means on a spec sheet, and when a dedicated sun lens is still the better choice.
Quick answer
Photochromic lenses contain molecules that react to ultraviolet (UV) light. Outdoors they darken, usually within a minute, and indoors they fade back to clear over a few minutes. They suit people who move between indoors and outdoors throughout the day. Most don't darken much inside a car, because windscreens block most UV.
How photochromic lenses work
The lens contains light-sensitive molecules. In plastic lenses these are organic dyes; older glass lenses used silver halide crystals. When UV light hits them, they change shape and start absorbing visible light, which darkens the lens. When the UV goes away, they slowly return to their clear form.
UV is the trigger, not brightness. That's why the lenses still darken on overcast days, when UV passes through cloud, and stay clear at night under headlights and streetlights, which give off little UV.
How fast and how dark depends on the product and the temperature. Manufacturers typically quote darkening within a minute, with fading back to clear taking about 2 to 5 minutes. In hot sun, lenses usually get less dark. In cool conditions they get darker but take longer to clear.
What "100% UV protection" actually means
You'll see this claim on almost every photochromic lens. It can be true, but only for a specific product, tested in a specific way. Here's how to read it.
It's a property of the lens, not the tint
UV blocking comes from the lens material and treatment. A good photochromic lens blocks UV whether it looks clear or dark. A dark tint on its own tells you nothing about UV protection.
It depends on the wavelength range
UVB and UVA run up to about 400 nanometres. "UV400" means the lens is specified to block UV up to 400 nm. If a spec says "100% UVA and UVB", ask what range was tested.
It's the manufacturer's claim
Branded photochromic lenses come with published specifications. Transitions, for example, states that all its lenses block 100% of UVA and UVB. Budget photochromics may not publish a spec at all.
Our commitment
Before you order, we tell you the UV specification of the exact lens you're buying, as published by its manufacturer. If a lens has no published UV specification, we won't describe it as UV-protective.
Why UV matters: long-term exposure to sunlight's UV is associated with cataract and pterygium (a growth on the white of the eye). Lenses only protect the light passing through them. UV can still reach your eyes from the sides and above, so a hat and wraparound frames add protection in strong sun.
What affects how photochromic lenses perform
| Factor | What it changes |
|---|---|
| Product and brand | Darkening speed, maximum darkness, fade-back time and UV specification |
| Temperature | Less dark in heat; darker but slower to clear in cold |
| Car windscreen | Blocks most UV, so most lenses stay light in the car. Some products are designed to darken partly behind the windscreen. |
| Tint colour | Grey keeps colours looking natural; brown gives a warmer look |
| Age of the lens | The darkening effect can weaken gradually after years of daily sun exposure |
Photochromic lenses compared
vs prescription sunglasses
Sunglasses stay dark all the time and work fully in the car. Photochromic lenses are clear indoors and usually lighter outdoors than a dedicated sun lens. If you drive a lot in bright sun, prescription sunglasses are the better driving pair.
vs polarised lenses
Polarised lenses cut glare reflected off water, wet roads and car bonnets. Standard photochromic lenses don't specifically do this. Some products combine both at a higher price. Neither type is for night driving; see our night driving glasses guide.
vs clip-on sun lenses
Clip-ons give a consistent dark tint on demand, including in the car, but they're an extra part to carry and can be lost. Photochromic lenses need no extra step.
vs blue light lenses
They do different things. Photochromic lenses respond to outdoor UV. Blue light filtering lenses are marketed for screen use, but a major 2023 review of the evidence found they probably don't reduce eye strain from computer work. For screen discomfort, an up-to-date prescription, breaks and good screen habits matter more than any lens coating.
Who photochromic lenses suit
Often a good fit: people who move in and out of buildings all day, such as school runs, site visits, errands and campus life. Also people who'd rather not carry and swap a second pair of glasses.
Children: can be practical for children who spend time outdoors at school, since there's no separate pair to lose. We discuss it alongside their children's eye test.
Progressive wearers: photochromic can be added to progressive lenses as well as single vision.
Less suited: people whose main need is sun glare while driving, and people who dislike any delay while lenses clear after coming indoors.
Photochromic lens cost in Kenya
Photochromic is added to the price of your base lens. The total depends on your prescription, the lens design and the brand. For reference, our progressive lens tiers start at KSh 8,500 (standard), KSh 15,000 (premium) and KSh 25,000 (ultra-premium), before photochromic is added.
We give an itemised quote after your eye test, showing the product, its published UV specification and the collection time, before you pay. The eye test is KSh 300, free with glasses.
Photochromic lenses at Ottico Eyecare
We start with an eye test, because an accurate prescription matters more than any lens feature. Then we look at whether photochromic suits your routine. We supply photochromic lenses from Essilor and Zeiss, plus lower-cost options.
Some photochromic lenses are made to order, so we confirm your collection time before you pay. Every pair comes with a 12-month warranty against manufacturing defects.
We're at Westbay Mall, 1st Floor, Unit 109, Red Hill Road, Gachie, with free parking. We see patients from Ruaka, Runda, Gigiri, Nyari, Kitusuru, Lavington and Tigoni.
Photochromic lens questions
Do photochromic lenses block 100% of UV?
Many branded photochromic lenses are specified by their manufacturers to block 100% of UVA and UVB, whether clear or dark. It depends on the product, so ask for the specification of the lens you're buying. We show it to you before you order.
Do photochromic lenses work in the car?
Most only partly, because car windscreens block most of the UV that triggers them. Some products are designed to darken partly behind the windscreen. For bright daytime driving, prescription sunglasses work better.
Do they work on cloudy days?
Yes. UV passes through cloud, so the lenses still darken, usually less than in full sun.
How fast do they darken and clear?
Typically within a minute outdoors, and a few minutes to clear indoors. It varies by product and temperature; lenses clear more slowly in the cold.
Can I wear photochromic lenses at night?
Lenses that return fully clear indoors stay clear at night, because there's little UV. Some extra-dark products keep a slight tint indoors. Ask us about the specific lens if you drive at night.
Are photochromic and "Transitions" lenses the same?
Transitions is a brand of photochromic lens. Other manufacturers make photochromic lenses under their own names.
Do photochromic lenses wear out?
The lens lasts like any prescription lens, but the darkening effect can weaken gradually after years of daily sun exposure.
Will photochromic lenses help with screen eye strain?
No. They respond to UV, not screens. Screen eye strain is usually best helped by an accurate prescription, regular breaks and good screen setup.
How much do photochromic lenses cost in Kenya?
It depends on your base lens, prescription and brand. We give an itemised quote after your eye test, which is KSh 300 or free with glasses.
Not sure if photochromic suits you?
WhatsApp us about your daily routine, or come in for an eye test and an itemised quote. Westbay Mall, Red Hill Road, Gachie. Monday to Friday 10:00 AM to 7:00 PM, Saturday 10:30 AM to 5:30 PM.