The black level test shows whether your screen keeps the darkest and brightest shades apart, the detail in shadows and highlights that picture settings most often crush. The run starts on numbered near-black squares, moves to near-white squares and a gamma chart, and ends on near-black gray fields and black, so you can see the effect of each setting you change.
Press Start full-screen test. Dim the room for the dark steps: Lagom’s test pages call a dark room and full screen essential for the black level test.
1. Black level: squares 1 to 24
Each square is one level lighter than the last, from 1 to 24 on a black (0) background. On an ideal monitor you can see all of them. If the first few melt into black, raise brightness (or the black-level setting) one step at a time until square 1 or 2 is just visible, without the background turning gray.
2. White level: squares 231 to 254
The same on white: each square should stand apart from the white background. Squares that disappear mean highlights are clipped; lower contrast until they come back. Lagom’s white saturation test uses the same idea with 12 checkerboard squares.
3. Gamma: the line chart
Each column holds alternating black and white single-pixel lines with a solid gray patch in the middle, mixed for gamma 1.8, 2.0, 2.2, 2.4 and 2.6. From a few steps back the lines blend into a gray. The column where the patch vanishes into its surround is your screen’s gamma; for an ordinary sRGB desktop you want it on 2.2.
The patch values come from the formula the chart relies on: lines of 0 and 255 average to half the light, so the matching gray is the level whose light is 50% at that gamma.
4. Near-black uniformity and black
Once black level is set, the 5% and 10% gray fields show whether the panel is even near black, and the black field shows bleed or glow.
If something is off
A full-range signal on a screen set to limited range makes squares 1 to 16 disappear and clips the top squares into white. The opposite mismatch, a limited-range signal (16–235) on a full-range screen, keeps every square visible but turns black gray and whites dull. Either way, match the graphics driver’s range with the screen’s. For banding in the ramps, use the gradient banding test; for a plain black, the black screen.