Why polarized sunglasses make your phone screen go dark or rainbow

Polarized sunglasses make some phone screens go dark because the screen itself is emitting polarized light. Cross the lens's axis with the screen's and almost nothing gets through. Turn the phone 90 degrees and the picture comes back. The rainbow bands some people see are a separate effect from a stressed plastic layer, usually a screen protector or a car windscreen, sitting between the screen and your lens. Neither the phone nor the glasses is faulty; this is polarization working exactly as designed, on a light source that happens to be polarized too.

Why the screen goes dark

An LCD screen works by polarizing light. The backlight is white and unpolarized; a filter in the panel lets through only one plane, and liquid crystals then twist that light pixel by pixel to make the image. The light leaving the screen is therefore vibrating in one direction.

A polarized lens blocks one direction of light. Almost every pair blocks the horizontal plane, because that is the plane glare arrives in. If the screen's light happens to be vibrating horizontally when you hold the phone a certain way, the lens blocks it, and the screen goes dark.

That is the whole explanation. It is the same effect as the screen test people use to check whether sunglasses are polarized, only here it is happening by accident.

Why the screen shows rainbow bands

The rainbow is a different effect. Some transparent plastics, when stressed or moulded, split light into components that travel at slightly different speeds. Put a layer like that between two polarizers, the screen's own filter and your lens, and the two components interfere, cancelling some colours and reinforcing others. You see bands of colour that follow the stress pattern in the plastic.

The usual culprits:

• A tempered-glass or plastic screen protector, especially a cheap one.
• A car windscreen, if you are looking at the phone through it or at a display behind it. Laminated windscreens are full of stress patterns.
• A phone case with a plastic front window.

Take the protector off and the rainbow usually goes.

Screens come up in one other sunglasses question, whether a tinted lens blocks their blue light; our blue light post answers that one.

Which screens are affected most

If you own a recent OLED phone and have never noticed the problem, this is why.

The three fixes

1. Rotate the phone. Turning it 90 degrees moves the screen's polarization out of line with your lens. This works for handheld screens instantly.
2. Change the screen protector. If the problem is rainbow bands rather than darkness, a different protector, or none, usually fixes it. Glass protectors vary; the cheapest ones are worst.
3. Keep a non-polarized pair for the car. If your dashboard is the problem, no rotation will help, because it is bolted in. Some drivers keep a non-polarized pair in the glovebox. Our polarized vs non-polarized post covers the trade-off.

There is no way to make a polarized lens pass polarized light at the crossed angle. That is what the filter is.

Is it a reason not to buy polarized?

For most people, no. Rotating a phone is a small habit, and the glare removal on a road, a lake or a beach is a large benefit. The people who should think twice are those whose job is reading a fixed LCD in bright sun: pilots, some boat skippers with older chartplotters, forklift and machinery operators. For everyone else it is a curiosity that explains itself once you know what you are looking at.

Every pair on this site is polarized, so all of this applies to them. If you spend most of your time behind the wheel, the T01 Grey is the neutral choice, and it is worth checking your own car's display through it before deciding.

Frequently asked questions