Free screen test
Fill the screen with solid colors to find dead or stuck pixels, light leaking from the edges, and uneven brightness. It runs in the browser on monitors, laptops, phones, and TVs.
Click or press → for the next color, ← to go back, Esc to finish.
What each color shows
A screen fault is a spot that stays the same while everything around it changes. That is why the test cycles plain colors: each one hides some faults and makes others obvious. Look at the whole screen on every color from your normal seat, then up close at anything suspicious.
| Color | Look for |
|---|---|
| White | Dark dots (dead pixels), dust, pressure marks, and a tint on one side of the screen. |
| Black | Lit dots (hot or stuck pixels), light leaking from edges or corners, and glow. |
| Red | Dots of another color. A stuck green or blue subpixel stands out on red. |
| Green | Stuck red or blue subpixels, and green or magenta tint shifts at the edges. |
| Blue | Stuck red or green subpixels. Blue is also the dimmest color, so dark dots are harder to see here. |
| Mid gray | Darker corners (vignetting), blotches, and the grainy “dirty screen” texture on large TVs. |
| Dark gray | Clouding on LCDs and faint vertical or horizontal bands on OLEDs. |
Dead, stuck, or just dust?
On most screens every pixel is made of a red, a green, and a blue subpixel, so a 4K screen has almost 25 million of them. The color of a faulty dot tells you which part failed:
- Dead pixel: black on every color. All three subpixels are off. Easiest to see on white.
- Stuck pixel: stays red, green, blue, or a mix such as yellow. One or two subpixels are stuck. Easiest to see on a color that differs from the stuck one.
- Hot pixel: white or very bright on every color. Easiest to see on black.
Many “dead pixels” turn out to be dust or a speck under a screen protector. Dust looks slightly soft and can cast a faint shadow when you look from the side; a pixel fault is perfectly sharp and exactly one pixel wide. If a dot moves when you drag a window over it, it is part of the picture, not the panel. A panel fault never appears in a screenshot, because a screenshot saves the image the computer made, not what the panel shows.
A dead pixel almost never recovers. A stuck pixel sometimes does, often after hours of ordinary varied content. Pressing or rubbing the panel can damage it and may void the warranty, so document the fault before you try anything.
Backlight bleed or IPS glow?
On black, most LCDs leak some light, and it shows up in two ways. Move your head while you look at the black screen:
- Backlight bleed stays in the same place and keeps its shape. It usually sits along an edge or in a corner and comes from uneven pressure on the panel layers. Heavy bleed is often treated as a defect.
- IPS glow changes brightness and shape as you move, often with a silver, amber, or bluish tint, and fades when you sit farther back. Almost every IPS panel shows it on dark content; it is not a defect.
A black screen in a dark room at full brightness is the worst case. Judge it again at your normal brightness with real content, such as a film with black bars. OLED screens have no backlight, so they cannot show bleed or glow at all. Cameras exaggerate leaking light: if you photograph it for a return, set the exposure so the photo looks like what you see, and note the brightness setting.
Uneven brightness and tint
No screen is perfectly even. Slightly darker corners are common on edge-lit monitors and laptops, which light the panel from LEDs along the edges. Mid gray shows that fall-off best. Dark gray shows clouding, the blotchy patches of edge-lit LCDs, and the faint bands some OLEDs show at very low brightness. On white, look for one side that looks warmer, greener, or pinker than the other.
Let the screen warm up for 20–30 minutes before you judge uniformity, because it shifts slightly as the panel and backlight heat up. Calibration cannot fix one dark corner, since it corrects the whole screen at once. Some professional monitors have a uniformity compensation mode that dims the brighter areas.
How many bad pixels are allowed?
There is no single rule. The withdrawn ISO 13406-2 standard is still widely quoted: its Class II allowed up to two always-lit pixels, two always-dark pixels, and five faulty subpixels per million pixels. It was replaced by ISO 9241-307 in 2008, and manufacturers now write their own policies, which differ by brand, product line, and region. Some promise zero bright pixels; others count by type and position. A retailer's return window is often easier to use than any pixel policy.
For a claim, take one close photo of the fault and one wide photo that shows where it is on the screen, then put them in a defect report with the colors it shows on.
Other tests
Input Lag Test
Compare the delay of two screens with one phone photo, or measure your full click-to-screen delay.
HDR Capability Check
See whether your browser and display report HDR, and which settings decide if HDR is really on.
Gradient Banding Test
Look for steps in smooth gradients and find out whether the file, the graphics settings, or the panel causes them.
Burn-in Test
Check OLED and plasma screens for burned-in shapes, and tell temporary retention from permanent wear.
Color Temperature Test
Compare white presets and Night Light on one fixed white to see how warm or cool the screen really is.
Text Clarity Test
Check small text for blur and colored fringes caused by scaling, ClearType, or the subpixel layout.
Touch Screen Test
Draw across a grid to find touch dead zones and count how many touches the screen reports at once.