Back in or around 2018 I was teaching an optics lab to non-physics majors — the kind of class where you're trying to make light and waves feel tangible to people who mostly just need the science credit. Excitement was tough to come by, but that didn't stop me from trying. One of my favorite experiments was dead simple: set up a light source, put two polarizing filters in the path, and have students measure the brightness at different angles between them. There's a formula that predicts exactly how much light should get through at each angle, and the point of the lab was to show that when you actually measure it, the data lands right on the predicted curve. Every semester a few students would be genuinely surprised that their messy real-world measurements matched the textbook math almost perfectly, like they expected physics to be less precise than that.
I think about that experiment a lot now, because that same formula — the same cos² relationship those students were plotting on graph paper — is the reason your polarized sunglasses black out your laptop screen. And understanding it is basically the entire foundation of this idea for MacBook sunglasses.
So let's get into it.
Light vibrates in a direction, and that matters more than you'd think
Okay so quick physics refresher. Light is an electromagnetic wave, and like any wave it has a direction it vibrates in — up and down, side to side, diagonal, whatever. Sunlight vibrates in all directions at once, which physicists call "unpolarized." It's just a jumble of waves going every which way.
A polarizing filter lets through light vibrating in one specific direction and blocks everything else. That's fundamentally what polarized sunglasses are — they're oriented to pass vertically vibrating light and block horizontally vibrating light. The reason that's useful is that glare (light bouncing off water, roads, car hoods, etc.) tends to become horizontally polarized when it reflects off flat surfaces. So vertical polarization is occasionally chosen in sunglasses to block that type of glare specifically, rather than just making everything darker the way regular tinted lenses do.
This is all well and good until you point your eyes at a screen.
Your laptop screen is also polarized, and that's where things get complicated
LCD screens don't just blast out random light. The way they actually work is genuinely clever — there's a backlight, then a polarizing filter, then a layer of liquid crystals that twist the light's polarization angle based on electrical signals (this is literally what each pixel is doing), and then a second polarizing filter on the front. So the light leaving your screen and hitting your eyes is always polarized at some specific angle.
And here's the thing that surprised us: there's no standard for what angle that should be. Different manufacturers pick different orientations for that front polarizer. Some screens are polarized vertically, some at 45 degrees, some circularly (we'll get into that). It can even vary between different products from the same company. Nobody coordinated this.
So when you put on any old polarized sunglasses and look at a screen, what happens depends entirely on the angle relationship between your lenses and that screen's output polarization. And there's actually a precise formula that describes it.
Malus's Law is weirdly elegant
Okay so fair warning, we're about to get into some math — the trigonometry stuff you probably hated in school. But stick with me because it's honestly not bad, and it's the key to understanding why any of this matters.
Back in 1809, a French physicist named Étienne-Louis Malus worked out the relationship between polarized light and a polarizing filter, and it's one of those equations that's simple enough to be satisfying:
Light passing through = cos²(θ)
Where θ is the angle between the light's polarization and the filter's orientation.
If you remember cosine from school, great. If not, don't worry — there's a deeper meaning to it, but practically speaking, all you really need to know is that cos²(θ) draws that squiggly curve you might recognize from textbooks (and from the image at the top of this post). It starts at 1 when θ is 0°, smoothly drops to 0 when θ hits 90°, and comes back up again. The cos² part is what makes the relationship interesting — it's not linear, the light doesn't dim proportionally as you increase the angle.
At 0° (perfectly aligned) you get 100% transmission, which makes sense. At 45° you're at cos²(45°) = 50%, so half the light gets through. But at 60° you're already down to just 25%. And at 90° — when the polarizations are perpendicular — cos²(90°) = 0. Complete blackout. Nothing gets through.
That 90° case is the moment when you're sitting outside and your laptop screen looks completely dead and you start pressing the power button before realizing it's your sunglasses. That's the same cos² curve students were measuring in lab — except now it's playing out on your $2,000 MacBook.
The random light thing is actually pretty cool
One detail we kept coming back to because it's just kind of neat — when unpolarized sunlight (vibrating in all random directions) hits a polarizing filter, you might expect the math for how much gets through to be complicated. You'd need to account for every possible angle of vibration and figure out how they all add up.
But when you actually do the integral and average cos²(θ) over all angles from 0° to 360°, the answer comes out to exactly 0.5. Not approximately, not "close to" — exactly half. Every time. Random light through a polarizer always loses exactly 50% of its intensity, as a mathematical certainty. The cosine-squared function just happens to average perfectly to one half.
This is kind of the whole foundation of why polarized sunglasses work. Ambient sunlight — the unpolarized jumble coming from everywhere — loses exactly half its intensity through your lenses. Glare off horizontal surfaces, which is strongly horizontally polarized, gets almost completely blocked (it's near that 90° perpendicular extinction angle). So you keep a reasonable amount of the general light around you but lose almost all of the painful reflected glare. Pretty clever for a piece of film.
How phones deal with this (the 45-degree compromise)
Phone manufacturers have actually thought about this problem more than laptop makers have, because phones get used in two orientations. If you hold your phone in portrait mode and then rotate to landscape, that's a 90° change — and if the screen's polarization was aligned with your sunglasses in one orientation, it would be at the worst possible angle in the other.
So a lot of phone screens put their front polarizer at 45° to vertical. This is a smart compromise: in portrait mode the angle between the screen (45°) and your vertical sunglasses is 45°, giving you cos²(45°) = 50% brightness. Rotate to landscape and the new angle is still 45° — just in the other direction. You get consistently dimmer viewing in both orientations, but no blackout in either. It's not perfect but it avoids the worst case scenario. This of course only holds true with vertically or horizontally polarized glasses.
Apple has iterated on this over the years with iPhones. Some early models had really bad blackout in one orientation. The iPhone 4 reportedly fixed it almost entirely. iPads have historically been worse — certain models go nearly completely dark in portrait through polarized lenses, which pilots have complained about since they use iPads on kneeboards in the cockpit.
Circular polarization: the screens that never black out (but always dim)
There's another type of polarization worth knowing about here — circular polarization. Instead of vibrating in a fixed direction like linear polarization, circularly polarized light sort of corkscrews as it travels. The electric field traces out a helix instead of a straight line.
Some newer screens (including certain iPhones and Samsung devices) use compensating films that convert their linearly polarized output into circularly polarized light before it leaves the screen. This is specifically designed to solve the sunglasses compatibility problem, and it mostly works — a circularly polarized screen won't black out at any rotation angle when viewed through standard linearly polarized sunglasses.
But there's a tradeoff that doesn't get talked about much. When circularly polarized light passes through a linear polarizer (your sunglasses), it always loses exactly 50% of its intensity regardless of how you orient the filter. It can't do better than that. Because the light is constantly rotating its polarization direction, the averaging effect is permanently baked in — there's no angle where you get full transmission, no sweet spot to find.
For phones this is a perfectly reasonable solution. You're holding the device in different orientations, you're usually looking at it for short periods, and "always 50% brightness" is way better than "sometimes 0% brightness." But for a laptop where you're working for hours in a fixed orientation and already fighting outdoor brightness, that constant 50% dimming of your screen adds up. You end up cranking brightness to max, burning through your battery, and still not getting the clarity you'd get with properly aligned linear polarization.
Laptops are different, and that's the whole idea behind Meridian
Laptops basically sit in one orientation. You're not flipping your MacBook between portrait and landscape. So the 45-degree compromise that makes sense for phones doesn't really apply here, and the circular polarization approach — while it prevents blackout — leaves a lot of screen brightness on the table.
What actually matters for a laptop is simpler: what's the linear polarization angle of the display, and can you match your sunglasses to it?
The catch is that laptop manufacturers don't agree on a polarization angle any more than phone manufacturers do. A ThinkPad might be polarized vertically, a Dell at 45 degrees, an older MacBook at a completely different angle — and there's nothing stopping a manufacturer from changing it between product generations. You can't just make one pair of "laptop sunglasses" and call it universal, because the angle you'd need to match is different for different screens.
That's actually why we focused specifically on MacBook Retina displays. Across the models we've tested, Apple has been internally consistent with their polarization orientation on the Retina lineup — which means we can align to one angle and have it work reliably across MacBook Pros and Airs. If you get that match right — if θ in Malus's Law approaches 0° — then cos²(θ) approaches 1. Nearly all of the screen's light passes through your lenses. Meanwhile, the randomly polarized ambient sunlight still loses its guaranteed 50%. Your screen appears relatively brighter than everything around it. The world dims but your display doesn't.
That's what we built Meridian around — that cos²(0°) ≈ 100% transmission case, instead of the cos²(45°) = 50% you'd get from a random pair of polarized sunglasses if you're lucky, or the cos²(90°) = 0% blackout if you're not.
Don't take our word for it — test it with yours
When you get your pair of Meridian glasses, you can verify everything in this post yourself. Hold them up in front of your MacBook screen and look through the lenses normally — you should see your display at full brightness, full color, very light dimming (due to additional coloring of the lenses). That's cos²(0°) = 100%, the polarization alignment we built them around.
Now slowly tilt the glasses to one side. You'll watch the screen start to dim as θ increases and cos² starts dropping. Keep going to about 45° and you'll be at roughly half brightness. Tilt all the way to 90° and the screen goes nearly black — full extinction, cos²(90°) = 0. Malus's Law playing out right in front of you in real time.
Then bring them back to level and the screen snaps back to full clarity. That peak brightness sitting exactly at the natural horizontal wearing position isn't an accident — that's the polarization angle of your MacBook's display, and it's precisely the angle we aligned to. Everything we've talked about in this post, you're holding the proof of it in your hands.
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Meridian: Sunglasses polarized for MacBook Retina displays. Order now →