Black level refers to the minimum luminance output of a display — how dark it can make individual pixels appear. In an ideal display, black would be 0 nits (no light emitted at all). LCD displays cannot achieve true black because the backlight is always on and some light leaks through the liquid crystal layer even when it is instructed to block all light. OLED displays can turn individual pixels completely off, achieving near-zero black levels. Black level matters because it determines the perceived contrast ratio of a display and the visibility of shadow detail in dark scenes. A display with poor (elevated) black level will show dark scenes as washed out and lack depth in dark content.

ANSI (American National Standards Institute) black level is measured using the ANSI contrast test — a 4×4 checkerboard of alternating black and white patches displayed simultaneously. The luminance of the black patches is measured using a colorimeter or spectrophotometer while white patches are also displayed. This is a more realistic measure than full-on/full-off contrast, which measures black while the entire screen is black (and the backlight dims automatically). ANSI black level reflects real-world black performance during normal use. A monitor that shows an ANSI contrast ratio of 1000:1 means its black level is 1/1000th the brightness of its white level in a checkerboard pattern.

OLED displays achieve true black by turning pixels off completely — they emit zero light when displaying black, resulting in an effectively infinite contrast ratio and perfect black level. LCD displays use a backlight that illuminates the entire panel; the liquid crystals act as shutters to block light. Even when fully closed, some light leaks through, resulting in a finite black level typically between 0.05 and 0.5 nits. VA (Vertical Alignment) LCD panels achieve the best black levels among LCD types, often reaching 0.05–0.2 nits. IPS panels typically have higher black levels (0.2–0.8 nits) but avoid the "black smear" effect of VA panels. TN panels generally have moderate black levels similar to IPS.

Gamma defines how a display translates digital signal levels (0–255) into actual brightness output. The standard gamma for sRGB and most consumer displays is approximately 2.2. At gamma 2.2, mid-gray (128 out of 255) is displayed at about 22% of the monitor's maximum brightness — much darker than the linear midpoint. If a monitor is set to a lower gamma (1.8 or 2.0), dark tones are lifted, which can make shadow detail more visible but reduces perceived contrast. If gamma is set too high (2.4+), dark tones become crushed and shadow detail disappears. The "black level" setting in many displays independently adjusts where the darkest signal (0) maps to in brightness, separate from gamma. Incorrect black level settings cause either "black crush" (shadow detail lost) or "lifted blacks" (black appears gray).

Auto Brightness Limiting (ABL), also called Automatic Brightness Limiter or ASBL (Automatic Sustained Brightness Limiter), is a power management circuit in OLED displays that reduces peak brightness when a large percentage of the screen is displaying bright content. When displaying a mostly white page, the OLED panel limits its brightness to prevent excessive power consumption and heat generation. ABL does not directly affect black level (individual dark pixels are still fully off), but it can make dark content adjacent to large bright areas appear differently. In practice, ABL is most noticeable when using a white-background application at full brightness, and it can cause the entire display to appear slightly dimmer.

To calibrate your monitor's black level using the PLUGE pattern: lower room lighting as much as possible and allow 5–10 minutes for your eyes to adapt. Set your monitor brightness to its minimum or near-minimum setting. View the PLUGE pattern — the center patch should be just barely visible above absolute black; the two flanking patches (slightly below and above the black reference) should ideally be invisible (below) and just barely visible (above). Adjust the monitor's "Black Level," "Shadow Enhancement," or "Brightness" control until this relationship is correct. For CRT and plasma displays, the "Brightness" control sets black level; for most modern LCD monitors, it is also labeled "Brightness" but affects backlight intensity. Some monitors also have a separate "Black Level" or "Low Light" control in the OSD.