A pixel is made of tiny light-controlling or light-emitting components, and the exact materials depend on the type of screen. On an LCD, each pixel is a sandwich of polarizing filters, liquid crystals, and color filters layered between glass. On an OLED screen, each pixel contains thin layers of organic compounds that glow when electricity passes through them. Every modern display technology builds pixels differently, but they all share the same goal: combine red, green, and blue light in precise amounts to produce any color you can see.
Inside an LCD Pixel
LCD pixels don’t generate their own light. Instead, they act as tiny shutters that control how much backlight passes through. The structure works like a stack of filters. Two sheets of polarizing film sit on the outside, oriented at right angles to each other. Between them, a thin layer of liquid crystal molecules is sandwiched between two glass substrates. When voltage is applied, the liquid crystal molecules twist or untwist, changing how light passes through the stack. More twist means more light gets through; less twist means the pixel darkens.
Color comes from a separate layer. Because liquid crystals alone can only control brightness, not color, a color filter sits in front of the liquid crystal layer. Each pixel is actually divided into three subpixels, each covered by a red, green, or blue filter. By independently adjusting how much light passes through each subpixel, the display mixes those three colors at different intensities to produce millions of visible shades.
Behind each subpixel sits a thin-film transistor (TFT), a microscopic electronic switch etched onto the glass. The transistor acts as a gatekeeper, holding a specific voltage for each subpixel between screen refreshes. A tiny storage capacitor (as small as 0.2 picofarads in high-density displays) keeps that voltage stable so the image doesn’t flicker or fade before the next update arrives. Without these transistors, you couldn’t address each pixel individually, and the image would blur.
Inside an OLED Pixel
OLED pixels work on a fundamentally different principle. Instead of filtering a backlight, each pixel emits its own light. The core of an OLED pixel is a thin film of organic semiconductor material, typically only a few hundred nanometers thick, sandwiched between two electrodes. The bottom electrode is usually indium tin oxide (ITO), a transparent conductor deposited on glass. The top electrode is a thin metallic layer.
When voltage is applied across these electrodes, electrons and positively charged “holes” flow into the organic layer from opposite sides, meet in the middle, and release energy as visible light. The color of that light depends on the specific organic molecules used. Some OLED displays use different organic materials for red, green, and blue subpixels. Others use all-blue OLED emitters and then convert some of that blue light into red and green using quantum dots or color filters, which can improve efficiency and color accuracy.
Because each pixel is its own light source, OLED screens can turn individual pixels completely off to produce true black. There’s no backlight bleeding through. This is also why OLED displays tend to be thinner: they don’t need the bulky backlight assembly that LCDs require.
How Subpixels Create Color
Regardless of display technology, nearly all screens rely on additive color mixing. Each pixel contains three subpixels: one red, one green, one blue. When all three fire at full intensity, the pixel appears white. When all three are off, the pixel is black. Every other color is a blend. A bright yellow, for instance, comes from red and green subpixels at high intensity with the blue subpixel dimmed. A deep purple blends red and blue with little green.
The number of brightness levels each subpixel can produce determines how many total colors the display can show. A standard 8-bit display offers 256 brightness levels per subpixel, which multiplies out to roughly 16.7 million possible colors per pixel. Higher-end 10-bit panels push that to over a billion. Your eye can’t distinguish all of them individually, but the smoother gradients between shades are noticeable, especially in photography or video content with subtle color transitions.
Quantum Dot Pixels
Quantum dot displays are a newer variation that enhances color purity. In these screens, a layer of nanoscale semiconductor crystals sits in front of a blue light source (either a blue LED backlight or a blue OLED). The quantum dots absorb the high-energy blue light and re-emit it as very precise wavelengths of red or green, depending on the dot’s size. Smaller dots emit bluer light, larger dots emit redder light.
This approach produces more saturated, vivid colors than traditional color filters, which work by blocking unwanted wavelengths (and wasting that light as heat). Quantum dot conversion is more efficient because it transforms light rather than discarding it. Samsung’s QD-OLED panels, for example, pair blue OLED emitters with quantum dot layers for the red and green subpixels, plus a filter to minimize blue light leakage into the wrong subpixel.
MicroLED Pixels
MicroLED is the newest display technology reaching consumers, and its pixels are perhaps the simplest to understand conceptually. Each subpixel is a tiny, individual LED chip made from inorganic semiconductor material (typically gallium nitride for blue and green, and aluminum gallium indium phosphide for red). There’s no liquid crystal, no organic film, no quantum dot conversion layer. Each chip directly emits its color.
The manufacturing challenge is placing millions of these microscopic LEDs with extreme precision. Current commercial MicroLED modules from LG Display have a pixel pitch of about 0.78 millimeters, which works well for large-format displays but is still too coarse for phone or laptop screens. The technology promises the self-emissive benefits of OLED (true blacks, wide viewing angles) with the durability and brightness of inorganic LEDs, which don’t degrade as quickly as organic compounds.
Plasma Pixels: A Legacy Approach
Plasma displays, common in the 2000s and now discontinued, took yet another approach. Each subpixel was a sealed glass cell filled with a mixture of noble gases, typically neon with 10 to 15 percent xenon. When high voltage was applied, the gas ionized into plasma and emitted ultraviolet light. That UV light then struck a phosphor coating on the cell wall, which converted it into visible red, green, or blue light, depending on the phosphor’s chemical composition. Red phosphors were europium-based compounds, green phosphors used manganese-doped materials, and blue phosphors relied on europium-doped barium magnesium aluminate.
This gas-discharge approach gave plasma TVs excellent contrast and color accuracy for their era, but the cells were physically large and power-hungry, which is why the technology couldn’t scale down to small screens and was eventually replaced by OLED.
Pixel Size and Density
The physical size of a pixel varies enormously depending on the display. On a modern smartphone with a 460 PPI (pixels per inch) screen, each pixel is roughly 55 micrometers across, smaller than a human hair. On a 27-inch 4K monitor, pixels are about 0.16 millimeters. On a large outdoor LED billboard, a single pixel might be 10 millimeters or more.
Pixel density is measured in PPI, the number of pixels lined up across one linear inch of screen. Higher PPI means smaller pixels packed more tightly, which produces sharper images at closer viewing distances. At typical smartphone viewing distance, anything above about 300 PPI is difficult for most people to distinguish as individual dots. For a desktop monitor at arm’s length, the threshold drops to around 100 to 150 PPI. The “right” density always depends on how far away you’ll be sitting.