A liquid-crystal display does not make light at each pixel. A backlight provides it, and layers in front control how much reaches your eyes. That makes an LCD fundamentally different from a self-emitting display.
A valve for light
Light passes through a polarizer, a liquid-crystal layer and another polarizer. An electrical signal changes the molecules’ alignment, which changes how the light passes the second polarizer. Red, green and blue filters divide pixels into colored subpixels; varying their brightness mixes the displayed colors.
Why black is not always black
Because the backlight is behind the panel, blocking light perfectly is difficult. Leakage and viewing angle affect dark scenes and contrast, while a bright backlight takes power. The exact arrangement varies by panel design. A camera sensor solves the reverse problem: it collects incoming light and turns it into electrical measurements.
Related: how a camera sensor converts photons into pixels.