How Displays Make Color: LCD, OLED, and the Subpixel

A display is a grid of pixels, and every pixel is really three tiny lights - a red, a green, and a blue subpixel, sitting side by side. They're far too small to resolve, so your eye blends them by optical mixing into a single perceived color. Set all three bright and you see white; set red and green bright with blue off and you see yellow. The screen never makes yellow light - it makes red and green light that looks yellow.

This is pure additive color: lights adding together, brighter as you add more, white at the top. It's the opposite of paint. And it means a display's whole job is to control the brightness of three lights per pixel, millions of times over. How it controls them splits the technologies: an LCD filters a shared white backlight; an OLED lets each subpixel emit its own light. Same three colors, two very different machines.

Put a drop of water on your phone screen and you can almost see them; magnify a patch here and you definitely can. A solid color, zoomed in, dissolves into a grid of red, green, and blue subpixels at different brightnesses. Displays arrange those subpixels in different layouts - simple RGB stripes, or clever shared patterns like PenTile - each a trade-off you can inspect.

Work it the other way: choose how bright each subpixel glows and watch the color they add up to. This is exactly what your device does when it draws a pixel - it looks up the three R, G, B values and lights the subpixels to match. Slide the three lights and build any color from scratch.

Two ways to set a subpixel's brightness. An LCD shines a constant white backlight through the whole panel; each subpixel has a color filter (letting through red, green, or blue) and a liquid-crystal shutter that twists to block more or less of it. An OLED has no backlight at all - each subpixel is its own little light-emitting diode, glowing exactly as bright as needed. See the light path of each.

That difference shows up most at black. To make black, an OLED simply switches its subpixels off - they emit nothing, a perfect, absolute black, and contrast is effectively infinite. An LCD can't turn off its backlight per pixel; it blocks it with liquid crystal, but the block leaks, so LCD black is really a dark gray. Compare a night scene on each.

The parts and terms behind the picture.

Six questions on subpixels, layouts, LCD versus OLED, and black levels. Instant feedback, no scores recorded - a wrong answer comes with a short explanation.

The subpixel connects to optical mixing, additive color, gamut, and the acuity that makes the trick work - here's where to go next.