An organic light-emitting diode, or OLED, makes light when electrical current passes through thin organic layers. Each luminous element can be driven separately. Unlike an LCD, it needs no panel-wide backlight shining through a shutter.
Light from the pixel
Electrical charges enter the organic stack and recombine, releasing energy as photons. A display controls the current and combines red, green and blue light to build an image. When a pixel is switched off, it emits no light, which helps an OLED panel render dark areas without a glowing backlight behind them.
Strengths and trade-offs
That advantage does not mean every OLED display is automatically brighter or more efficient in every scene. Materials, color, brightness, aging and heat affect performance. A static bright image can stress some pixels more than moving content. The underlying electroluminescence is related to conventional LEDs, but OLEDs use carbon-based light-emitting materials.
Related: how an LED turns electricity into light.