THE GUIDE
What the filter actually does, and how to choose the right strength for a screen
Blue light glasses are the most asked-about thing we sell, and the most misunderstood. Here is the short version — what the filter does, what really causes the ache at four o'clock, and the choice that matters more than the filter itself.
Blue light is not damaging your eyes
It is simply the short-wavelength end of visible light, and the sun is by far the biggest source — a few minutes outdoors delivers more of it than a full day at a laptop, even in November. There is no good evidence that screen-level blue light harms the eye. So if your eyes hurt by five o'clock, something else is doing it.
Three things actually tire your eyes
You blink about half as often. Concentration suppresses the blink reflex, the tear film dries, and you get that gritty, burning feeling by mid-afternoon. This is the most common cause by some distance.
You hold one focus for hours. The focusing muscle inside the eye stays contracted for as long as you look at something close — from the first email to the last.
Past forty, that focus becomes work. The lens in the eye stiffens with age, and it starts years before you reach for reading glasses. Many people meet it not with a book, but as an ache at the end of a screen day.
Choose your strength for the screen, not the book
This is the part that changes how a screen day feels, and almost nobody is told it. A lens brings one distance into focus — so the strength that is perfect for a paperback at 36 cm is usually too strong for a monitor at 50–70 cm. It pulls you forward and narrows what you can see clearly. Most people want half a step lower at the desk.
| Age | Book (36 cm) | Screen (50–70 cm) |
|---|---|---|
| 40–45 | +1.0 | +1.0, or 0.0 for filter only |
| 46–55 | +1.5 to +2.0 | +1.0 to +1.5 |
| 55+ | +2.0 to +2.5 | +1.5 to +2.0 |
Check it in two minutes. Sit as you normally would and read a few lines on screen. If you drift closer, go half a step up. If the text is sharp but feels tight and magnified, go half a step down. Between two strengths, always take the weaker one. Ours run from 0.0 to +4.0 — choose 0.0 for the filter with no magnification at all.
What the filter does
Every GLAS blue light lens is doing four jobs at once. It filters the harsh blue-white glare of phones and laptops. It carries a multi-layer anti-reflective coating, so the reflections bouncing off your screen and the lights above it stop landing in your eyes. It blocks UV. And it carries your reading strength, if you need one.
That last one is the quiet workhorse. Many customers tell us a long day simply feels easier with a pair on — and the filter costs you nothing to have: no tint, no loss of clarity, no compromise on how they look. For anyone past forty, the strength does real work, and the best part is that you never have to choose between the two. It's all one lens.
And no, the lenses are not blue
This is the question we get more than any other, usually from someone about to order. The lenses are clear — a CR39 lens with anti-reflective and scratch-resistant coatings plus UV protection. No blue cast, no yellow wash, none of the amber tint of gaming glasses. They look like ordinary glasses, because that is what they are.
Why one pair ends up living at the desk
Your strength, or none at all. From 0.0 to +4.0, no prescription, no appointment. Choose 0.0 and you get the filter and the frame with no magnification whatsoever.
Clear lenses, so you can wear them anywhere. No amber tint means nothing to take off before a meeting, a video call or dinner. Screen glasses you'd actually be seen in.
Built to be worn every day, not just at a desk. CR39 lenses with anti-reflective and scratch-resistant coatings and UV protection, in the same frames as the rest of the collection.
Rated 4.6 out of 5 by nearly 5,000 customers. The most common thing they tell us afterwards is that they bought a second pair, so there is one at the desk and one in the bag.
Four habits that help more than any lens
Every twenty minutes, look at something twenty metres away for twenty seconds — the single most effective thing you can do. Push the screen back to arm's length, top edge just below eye level. Match its brightness to the room rather than letting it blaze in a dark one. And blink deliberately, especially on video calls.
When to see an optician
A ready-made lens is a good place to start, not to stop. Book an eye test if one eye reads better than the other, if headaches arrive with the right strength, if your distance vision has changed, or if nothing ever feels quite right. Every two years is sensible, more often after fifty.