Not all blue light is the enemy

Most of what you have read about blue light treats it as one substance to be avoided. It is not. It is a stretch of the spectrum, and the parts of it do opposite jobs: one end stresses the eye, the middle runs your body clock, and the warm end is where the eye recovers. Knowing which is which is the whole of it.

The five bands of light

Every lens is a decision about which of these to keep and which to cut. Before the lenses make sense, the bands do.

Good blue, bad blue, and the difference is when

"Blue light" is not one thing, and it is not the villain the category has made it. It is a stretch of wavelengths, and the parts of it do different jobs. Reading left to right along the bar above:

• UV, below 400nm. Invisible, and no use to the eye at all. Long exposure is associated with cataract and surface damage, which is why every lens we make blocks 100% of it, day and night. This one is simply bad.
• HEV violet, roughly 400 to 440nm. The highest-energy light you can actually see. It scatters more than other wavelengths, which is what makes bright screens and glare feel harsh, and it carries no benefit for your body clock. This is the closest thing to "bad blue", and it can go at any hour.
• Circadian blue, roughly 460 to 480nm. The important one. Cells in your retina read this band and tell your brain what time it is, which sets alertness in the morning and melatonin at night. It is not bad light. It is good light at the wrong hour that causes the problem.
• Green, roughly 490 to 560nm. Most of what you perceive as brightness. Mildly active on the body clock, and the band you most want to keep intact if colours are to stay usable.
• Warm and red, above 560nm. The gentle end. It does not suppress melatonin, so it is the light you can sit in late without paying for it the next morning.

So the honest version of the story is not blue light versus no blue light. It is timing. In the morning, circadian blue is exactly what you want reaching your eyes, because it is the signal that starts your day. After dark it becomes the thing keeping you up. The same wavelength, the same eyes, an opposite effect eight hours apart.

Which is why a lens that blocks everything blue, worn all day, is the wrong tool. It flattens the signal your body clock runs on, and you end up dimmer in the morning without sleeping any better at night.

See the world through the lens

Hover or tap a lens to preview how it changes the view. It is a quick feel for what each one does to the light, rather than a colour-accurate render.

What each lens does with the light

You don't need any of this to wear them. But if you like knowing how a thing works, here is what each lens keeps and what it cuts.

Warm red and near-red light is restorative for the eye. It nourishes the cells at the back of the eye and is linked to healthier ageing. Cutting all the light would be easy. Knowing which light to keep, the gentle, warm end, while removing the harsh, high-energy end, is the whole craft.

Light-touch, and true to colour.

The most discreet lens we make. It blocks 100% of UV and cuts the deepest, harshest violet-blue, but it lets the rest of the blue through, including a good measure of the circadian-peak band (roughly 450 to 500nm) that helps set your body clock. A lighter filter than the others, on purpose: colour stays truest to life, which is what you want for screens, gaming or a film. The clear look is part of it.

Harmful blue out, daytime blue in.

It blocks 100% of UV and all of the harmful blue, then lets a measured, deliberate amount through in the 450 to 500nm band, the circadian-peak light your brain reads as daytime. Enough to keep your body clock set, none of the harsh, high-energy end. Protection that works with your day rather than against it.

The hybrid. The one that does everything.

A touch deeper than the yellow, with the fullest blue protection of the daytime lenses, while still letting just enough through to keep your body clock set. It is as at home on a screen as it is outdoors, where it lets you take in the sun's benefit without the harm. If you want a single lens that does almost everything, and looks its best doing it, this is the one.

Zero blue. Only warm light.

For the last hours before sleep. It lets through no UV and no blue light at all, right up through green, so nothing signals daytime to your brain. Only warm red light comes through, which means the melatonin your body makes for sleep is left undisturbed. Wind down, protected.

A lens that blocks all blue is not protecting you. It is switching off a signal you need.

Still deciding which one is for you? The buyer's guide works through it in plain English, and the size guide covers the fit.