A glossary of display brightness terms
Twenty-two terms that turn up constantly in writing about displays, defined without the marketing language.
Light and measurement
Luminance — the amount of light leaving a surface in a given direction. This is the physical quantity a brightness control changes.
Candela per square metre (cd/m²) — the unit of luminance. An ordinary office monitor peaks somewhere between 250 and 350; a phone in sunlight may exceed 1000.
Nit — an informal name for one candela per square metre. The two are interchangeable.
Lux — a measure of light falling onto a surface, used for room lighting rather than screens. A dim living room might be 50 lux; an office around 500.
Ambient light — the general illumination of the room your screen sits in. It determines what brightness will feel comfortable more than any other factor.
How panels make and control light
Backlight — the light source behind an LCD panel. Adjusting brightness on an LCD means adjusting this, not the pixels.
LCD — liquid crystal display. The crystals act as shutters that let more or less backlight through; they emit nothing themselves.
OLED — a panel where each pixel emits its own light. There is no backlight, so black pixels are simply off.
Mini-LED — an LCD whose backlight is divided into many small zones that can be dimmed independently, giving deeper blacks than a uniform backlight allows.
Local dimming — the technique of driving those zones separately according to the image.
PWM (pulse width modulation) — dimming a light by switching it on and off very rapidly rather than reducing its current. Efficient, but perceptible as flicker to some people at low frequencies.
Flicker-free — a manufacturer claim that a display dims by varying current, or switches fast enough that flicker is not perceptible.
Image characteristics
Contrast ratio — the ratio between the brightest white and the darkest black a display can show at the same time. Lowering the backlight preserves it; overlaying a dark layer in software reduces it.
Gamma — the curve mapping signal values to emitted light. Adjusting gamma changes midtones without moving white or black, which is how software dimming can darken an image without touching the backlight.
Colour temperature — the tint of the display's white, measured in kelvin. Lower is warmer and more orange; higher is cooler and bluer.
White point — the specific colour a display produces when asked for pure white. The standard target for most work is 6500 K.
HDR — high dynamic range. A mode allowing much brighter highlights alongside dark shadows. Enabling it often raises overall backlight output and can make the standard brightness control behave unexpectedly.
Communication between computer and display
DDC/CI — the display data channel command interface: the mechanism letting a computer read and write a monitor's settings, including brightness, over the video cable. Explained at length in its own article.
EDID — the block of identity data a display publishes so the computer knows what it is and which resolutions it supports.
VCP code — a numbered control in the command interface. Brightness is code 16; contrast is code 18.
OSD — the on-screen display, meaning the monitor's own menu, driven by its physical buttons or joystick.
Behaviour and features
Adaptive brightness — automatic adjustment based on a light sensor reading the room.
Content adaptive brightness — automatic adjustment based on the image being displayed, intended to save power.
Bias lighting — a low, neutral or warm light placed behind a screen to raise the brightness of its surroundings, reducing the contrast between display and room.
Night light — the Windows feature that warms the colour temperature of the output on a schedule.