Monitor Test

What monitor test does

A monitor test displays a series of full screen fields and tells you what a fault looks like on each one. The order matters more than most people expect: black first for backlight bleed and stuck pixels, white for dead pixels and dust, then red, green and blue individually to catch a fault in a single subpixel, then grey and a gradient for uniformity and banding. Run it when a screen is new and still returnable, before buying anything used, and before a warranty expires.

How to use it

1. Clean the screen first, so dust is not mistaken for a pixel fault.
2. Dim the room. Backlight bleed and dark-end problems are invisible in bright light.
3. Go full screen and work through the steps in order, reading what to look for on each.
4. Look across the whole panel each time, corners included, from about arm's length.
5. Note anything you find, then check it against the dead pixel, uniformity or burn-in pages.

About monitor test

Why this order finds more than random colours

Each field exposes a different class of fault, and some hide others. Black switches the pixels off, so anything stuck lit stands out and backlight bleed becomes visible at the edges; nothing else reveals either. White drives everything to maximum, which is the only way a fully dead pixel appears. The primaries each drive one channel alone, which is the only way a single failed subpixel shows, since the other two channels mask it on every mixed colour. Grey sits at partial output where panels are least uniform, and the gradient is the only field where banding appears at all.

What backlight bleed is, and how much is normal

Backlight bleed is light escaping around an imperfect seal at the edge of an LCD panel, and it appears as pale clouding in the corners on a black field in a dark room. Almost every edge-lit LCD has some. What matters is whether it is even and faint, which is normal, or a bright patch or streak, which is not. OLED panels do not have this problem at all, because there is no backlight. Be careful comparing against review photographs: a long camera exposure exaggerates bleed dramatically, so panels always look worse in pictures than in person.

Banding, and why the gradient step exists

A gradient should be a continuous ramp. If you can see distinct steps or stripes, the panel is not resolving all the levels it is being sent, which is banding. It usually means an 8-bit panel handling content smoothly enough for most purposes but not for gradients, or a panel using dithering to simulate more levels than it has. It is most visible in dark blues and greys, which is why those are where you should look hardest. Banding is a limitation to know about rather than a defect to return a screen over, unless it is severe.

Viewing angle, and why you should look straight on

Most of these checks assume you are square to the screen. LCD panels shift in brightness and colour when viewed off-axis, and the effect varies a lot by panel type: TN panels shift dramatically, VA panels less so, IPS least. If you move your head and the dark areas lighten or take on a purple cast, that is IPS glow rather than a fault, and it is normal for the panel type. Judge uniformity from one fixed position, centred, at arm's length.

When to act on what you find

Timing matters more than severity. Inside a retailer's return window you can usually send a display back for any reason, which is far easier than a warranty claim. Under warranty, manufacturers work to the ISO 9241-307 class system and typically allow a small number of faulty subpixels before replacing a panel, with the threshold varying by brand and screen size. Some premium monitors carry a zero bright pixel guarantee, which is a stronger promise and always stated explicitly. Test on the day it arrives, not a month later.