Monitor test
In fullscreen, the arrow keys and space change colour. Press Escape to leave.
Runs entirely in your browser · nothing is recorded, saved or uploaded
Fills the screen with solid colours so you can judge a monitor as a whole: uniformity across the panel, backlight bleed at the edges, and colour casts that are invisible against normal content.
How to use the monitor test
This is the same set of screens as a dead pixel test used for a different question. There you are hunting a single wrong dot; here you are judging the panel as a surface, and what you are looking for is unevenness — a corner dimmer than the centre, a patch with a colour cast, a gradient across a field that should be flat.
Backlight bleed shows on the black screen and only in a dark room. Light leaks around the edges of an LCD panel because the backlight is always on behind it — black on an LCD is a closed shutter, not an absence of light. Some bleed is normal on any edge-lit panel; large bright patches or obvious corner glow are not. OLED screens have none at all, because each pixel emits its own light and black means genuinely off.
Uniformity shows best on the grey and white screens. Cheaper panels are noticeably brighter in the centre, and a colour cast toward one side is common on large IPS displays. Whether it matters depends entirely on the work — invisible for text, disqualifying for photo editing.
One genuine limitation: a browser cannot measure any of this. There is no API for panel brightness, colour accuracy or contrast, so what this page gives you is a controlled surface and your own eyes. Actual measurement needs a colorimeter, and no web page can substitute for one.
Questions
Light leaking around the edges of an LCD, visible on a black screen in a dark room. Some is normal on edge-lit panels; large patches are not.