If computer screens render different colours by filtering white background light through red, green and blue pixels, and black is the absence of colour, how do computer screens reproduce the colour black?

Question

The most intuitive answer would seem that black pixels get “switched off”, but I know that’s not true because I can tell when a monitor is switched on and off even if the screen is just black. There’s a sort of “black glow” to them.

In: Engineering

Answer 1

So this applies to LCD, and other screen panel types where the pixels dont produce their own light.

On an lcd the backlight is always on in some form, and the way they make “blacks” can be done in a few diffetent ways and a combination of ways.

LCDs generally have a layer behind the pixels that is a polarizing layer, that can be turned on and off to block the backlight from going through that zone of pixels. What you reference when you know your monitor is on but supposed to be black is called “backlight bleeding”

Fancier LCDs use a technique called Local dimming where the backlight is a panel of millions of white LEDs broken into a grod of zones,i beleive current high end lcds have 192+zones of dimming. This is where the tv will actually shut off areas of the backlight to produce a much deeper black, though this effect can create “halos” most noticible on white text on a black background.