Light varying lenses (from tinted to clear)

Hi guys,

Am looking for people's experience on those light changing lenses - you know the ones that change from clear to tinted depending on the light exposed to them. I need to go get my eyes tested again and I'm a little sick of having to squint on sunny days, but at the same time I'm not planning on getting contacts (dislike how they feel).

So anyone have anything interesting to say about them? Are they any good?

Cheers.

Daisies

Transitions/reactions are great lenses. There are some things you should be aware of
1) The lenses work by being exposed to UV light so they dont tend to darken much in a car as the windscreen will block a lot of UV.
2) Also the lenses actually work better in the cold, so cold bright days ,make the lenses darker than bright warm days.
3) When they darken they tend to darken quickly but to go back clear again it takes longer. This process tends to speed up with use but most people are surprised that it takes a longer time.

Im sure there's other thinkgs to but my head is fried. If I think of any more i'll post again

'Reaction' lenses, that's the name of them. I assume you can tell from my post that I couldn't remember the name of them, thanks

Anyone else have experiences of them thus far?

The_Minister

From New Scientist:
http://www.newscientist.com/article/mg18825202.300-tainted-tint.html

I have a photochromic coating on my glasses. Under a blazing Caribbean sun they were only moderately tinted. However, under a weak midwinter sun in the UK they go almost black. Why?

We have two types of explanation here: one physical, one chemical. It seems likely that chemistry is responsible for the greater effect - Ed

I can only assume the questioner was walking around in the Caribbean, rather than lying on his back getting a tan. If so, the following may explain his experience.

The sun would be fairly low in the British winter sky, its rays shining almost directly on, and perpendicular to, the vertical plane of his lenses. In the tropics, the sun could be almost directly overhead, and if he was walking around, the sun's rays would strike his glasses edge-on. A sliver of radiant energy would be all that each lens would receive, thus reducing their shading reaction.

Charles Kluepfel, Bloomfield, New Jersey, US

One of the little details opticians fail to mention about photochromic glasses is that they do not work as well when hot. Particles of silver halide trapped inside the glass are normally transparent, but when struck by ultraviolet light, they disassociate into halogen and metallic silver, which darkens the lenses.

As both components are trapped inside the glass, they will recombine when UV light is removed - when you go indoors - becoming transparent again. The recombination reaction, like many others, speeds up as the temperature rises. As the darkness of the glasses at any moment is a balance between UV light-induced disassociation and the temperature-sensitive reassociation, it takes much more UV to reach a given level of darkening in a warm climate.

Alec Cawley, Newbury, Berkshire, UK

Photochromic materials are sensitive to temperature and darken more when they are colder. My sunglasses turn really dark on an overcast day but change little in the midday sun of Florida. This is fine for skiers but not much use to sun-lovers.

I also found, to my cost, that many photochromic lenses react almost entirely to ultraviolet radiation rather than to visible light, so they don't darken properly inside a car.

William Darlington, Bell College of Technology, Hamilton, Strathclyde, UK

The response of photochromic lenses to light is affected by temperature. Lower temperatures change the kinetics of the photochemical reaction so the reverse reaction - lens lightening - is delayed.

Photochromic lenses become much darker at lower temperatures. Living in the American Midwest provides me with perfect experimental conditions to test the temperature effects. With summer temperatures around 30 °C my photochromic lenses respond with a bluish-grey tint, whereas in deep winter, at around -10 °C, they quickly become very dark.

The darker lens tint on sunny winter days is especially beneficial against strong snow-dazzle. However, this heavy darkening is disconcerting when going indoors on a sunny day because it takes about 10 minutes for the lenses to return to normal.

Barry Timms, University of South Dakota, Vermillion, US

Kwekubo

Have you considered getting a pair of prescription sunglasses? Especially since many places do two-for-one offers, you could get one normal pair and a pair with tinted lenses.

brianthebard

I have reactions, they are great. You can get uv filter lens as well now I think that don't change colour but do the same thing.

anonymous_joe

Really handy even if my glasses do sometimes end up looking like something out of the Matrix.

I found that when I was in Brazil they got almost as dark as my sunglasses (proper Ray Bans) so I was pleasantly surprised. They're bloody handy if you're sensitive to light but... there's always a but... you get used to them. So you get used to not dealing with light so when you do have to face it it's all the worse.

But I'd recommend them whole heartedly.