White Screen Test: Check Dead Pixels and Backlight Bleed
White Screen Test. Click Start White Screen Test to fill your display with pure white and spot dead pixels, dust and dark spots. Use the free black screen test to confirm whether your monitor shows this issue before you adjust settings or return it.
Interactive Tool
White Screen Test fills your entire display with a pure white field so you can scan for dead pixels, dust, smudges, and faint dark spots that stay invisible against normal content. Click Start White Screen Test to open the pattern — iPhone's Safari has no native Fullscreen API, so the test drops into a pseudo-fullscreen overlay there instead, giving you the same edge-to-edge white field either way — then use the arrow keys or on-screen controls to step through the rest of the color sequence.
Bought a new monitor, or wondering why your old one looks patchy? This white screen test tool fills your monitor, laptop, phone or tablet with a solid white background right in your browser, so dead pixels, uneven brightness, tints and trapped dust stand out in seconds instead of hiding behind everyday content.
What a Free White Screen Test Reveals
A check like this works because pure white asks every pixel on the display to light its red, green and blue elements at full strength at once. A plain screen with no icons, text or photos gives your eye nothing to follow except the faults themselves. There is no download: the page draws the white screen itself, so any device with a browser can run it.
Dead Pixels and Stuck Pixels on a Bright White Screen
On a bright white screen, dead pixels show up as tiny black dots, because a dead pixel cannot light any of its subpixels. Stuck pixels look different: a stuck pixel holds one color, so it appears as a red, green or blue speck that never changes. Stuck pixels sometimes respond to pixel-fixing software that flashes rapid colors; true dead pixels almost never come back.
Backlight Bleed and Light Leakage
A white field shows where the backlight is uneven, but it is a poor tool for backlight bleed itself. Light leakage is easiest to judge on a dark field, where bright spots and edge glow along the frame stand out. Use white to map evenness, then confirm any suspected backlight bleed on black.
Screen Uniformity and Color Tint
Good screen uniformity means the white looks the same in the center, the edges and all four corners. Watch for warm tints that drift towards yellow, cool tints that lean blue, and brightness variations between zones. Before blaming the hardware, switch off Night Light and similar eye-comfort modes: the color temperature setting moves the white point, which can create a color tint that has nothing to do with poor color uniformity.
Dust and Scratches, Fingerprints and Smudges
A bright, empty field exposes fingerprints, smudges, lint trapped under a screen protector, hairline scratches and pressure marks. These can mimic dark spots, so if a mark moves when you wipe it, it was dirt, not one of the pixel defects you are hunting.
How to Run the White Screen Display Test
A careful display test takes only a few minutes. These steps make your white screen tests repeatable.
Clean the Panel and Let It Warm Up
- Wipe the glass with a dry microfiber cloth, never a sprayed liquid.
- Let the screen warm up for a good while first; color and output drift while it is cold.
- In your display settings, turn off vivid mode, dynamic contrast and HDR so you see the native picture.
- Dim the room lighting, but save a fully dark room for the black-screen pass.
Enter Fullscreen Mode and Scan Every Corner
Click the white area, then press F11 on a desktop (or tap the fullscreen icon on mobile) so the browser bars disappear; press Esc to leave. Fullscreen mode matters because the address bar and taskbar cover exactly the edges where faults tend to sit. Set the operating system to the display's native resolution, since scaling can blur a single bad dot into its neighbors. Start at maximum brightness, scan in rows from the top-left corner, then step back to your normal viewing position and viewing distance. A fault visible only up close, at an odd viewing angle, rarely matters. A full screen pass at two brightness levels catches more than one long stare.
Repeat With a Black Screen and Solid Colors
White is only one of the colors in a complete screen test. Switch to each solid color in turn, because each one isolates a different fault:
| Screen color | What it reveals best |
|---|---|
| White | Dead or unlit dots, dust, tint and brightness uniformity |
| Black screen | Backlight bleed, corner glow and bright pixels |
| Red, green, and blue | Single color channels stuck on or off |
| Gradients | Color banding and uneven tone steps |
A dot that stays black on every color is dead; a dot that only disappears on one color is stuck. Run the black screen pass last, in a dark room, once your eyes have adjusted.
Dead Pixel Test Allowances: How Many Faults Are Acceptable
Finding a fault during a screen test is half the job; the rest is deciding if it merits a return. Every manufacturer sets its own limit, and most still echo the old ISO 13406-2 classes, which count faults per million pixels across the whole panel.
Bright Pixel vs Dark Pixels: Which Faults Count Most
The standard splits faults into three types: a bright pixel that is always lit (Type 1), dark pixels that never light (Type 2), and single faulty subpixels (Type 3). A lit fault is far easier to see than a dark one, so strict policies allow zero bright pixels even when they tolerate a few dark ones.
Worked Example: A 27-Inch 1440p Monitor
Take a 27-inch screen at 2560 × 1440. It holds 3,686,400 pixels, or about 3.69 million. Its density follows from the diagonal:
$$\text{PPI} = \frac{\sqrt{2560^{2} + 1440^{2}}}{27} \approx 108.8$$That makes each pixel 0.233 mm wide (25.4 ÷ 108.8). Seen from 75 cm, one pixel spans 1.07 arcminutes, just above the 1-arcminute detail limit of 20/20 vision, so a single dead pixel is visible but only barely.
The same size screen at 3840 × 2160 drops to 0.71 arcminutes, while a 24-inch 1920 × 1080 screen rises to 1.27. Under Class II (2 bright, 2 dark and 5 subpixel faults per million), the allowance scales like this:
| Fault type | Class II per million | 27-inch 1440p allowance |
|---|---|---|
| Bright (Type 1) | 2 | 7 |
| Dark (Type 2) | 2 | 7 |
| Subpixel (Type 3) | 5 | 18 |
At 1080p the same class allows 4, 4 and 10 faults; at 4K it allows 16, 16 and 41. In other words, a screen with six dead pixels can still be "in spec," which is why the shop's rules matter more than the standard.
Return Window, Warranty and Pixel Policy
Test on the day the display arrives. A retailer return policy usually accepts any visible fault inside the return window, while the maker's pixel policy only grants a warranty replacement once you pass its fault count. Buying used devices, such as a second-hand monitor, run the check before you pay, because cover may no longer apply.
Judging a Second-Hand Laptop With a Screen Test
I am meeting a seller about a used 15.6-inch notebook, 1920 × 1080, listed at $412.50, and I have one question to answer before paying: is the screen good enough to keep, or worth a price cut? The short answer from the white screen test: two dark dots, both inside the Class II limit, but one sits where I would see it every day.
I wipe the glass, open the page, tap fullscreen and scan in rows. Two specks show up: one about 3 cm left of center, one near the bottom-left corner. Before calling them faults I switch to red, green and blue. Both stay black on all three, so they are dead dots, not lint. A black field is useless for this check, by the way: a dead dot disappears into black, so only the bright colors confirm it.
Next, the math. The screen packs 2,073,600 dots, so Class II allows 4 dark faults (2 × 2.07, rounded down). Two is in spec. Size is the real issue. At 141.2 PPI each dot is 0.180 mm wide, and how visible it is depends on distance:
| Eye distance | Angular size | Visible to 20/20 eyes? |
|---|---|---|
| 40 cm (leaning in) | 1.55 arcmin | Clearly |
| 52 cm (my desk) | 1.19 arcmin | Yes |
| 70 cm (docked, arm's length) | 0.88 arcmin | Barely, if at all |
I solved for the break-even point: below about 61.8 cm, a single dot on this screen exceeds 1 arcminute. I recompute it by hand (0.180 ÷ tan(1/60°)) and get the same figure. Since I work at 52 cm, the center dot will show on every white document.
My judgement: the corner dot does not matter, the center one does. I offer $360, citing the center fault, and plan to run the check again on day one inside the seller's 14-day return promise. The caveat worth knowing is that "in spec" only describes the count; it says nothing about position, and position is what decides whether you notice it.
White Screen Testing on Different Devices
White screen testing follows the same idea everywhere, but each type of hardware hides faults in its own places.
Testing Desktop Monitors
When testing desktop monitors, repeat the screen test on every input you use, HDMI and DisplayPort alike, since a bad cable can add sparkles that look like faults. Confirm the refresh rate in system settings too: some screens only show flicker or noise at higher refresh rates.
Testing Laptops
Testing laptops adds mechanical checks. Open the lid to several angles, because pressure from the hinge or a flexed bezel can create pale blotches. If the screen dims in steps, look for PWM flicker by filming it with a phone camera.
Testing TVs
Open the page in a smart TV browser or through a streaming stick. Turn off motion smoothing and local dimming first, since both alter a flat field, then judge the TV from your sofa, not the stand. The same approach works on projectors.
Testing Phones and Tablets
Testing phones is quick: disable auto-brightness, set brightness by hand, tap fullscreen, lock rotation, and turn on Do Not Disturb so notifications do not cover the edges mid-scan.
How Panel Type Changes a White Background Check
Your panel type decides which faults are defects and which are normal behavior. A white field reads differently on an LCD panel than on a self-lit screen.
IPS Glow on LCD Screens
On IPS panels, a silvery sheen in the corners that shifts as you move your head is IPS glow, a normal trait of the technology. Bleed stays fixed in place whatever your viewing angles. Most LCD screens show a little of one or the other.
OLED Screens, Burn-In and Screen Retention
OLED screens have no backlight, so there is nothing to bleed, but they can carry burn-in: faint ghosts of taskbars or logos that a white field makes obvious. Temporary screen retention fades within minutes; the permanent kind does not. White also maximizes power consumption on OLED, so keep test sessions short.
What a Screen Tester Cannot Measure
A browser screen tester shows faults but cannot measure picture quality; that takes instruments and proper screen calibration.
Color Accuracy Needs a Hardware Colorimeter
Your eyes adapt to whatever white they see, so they are poor judges of color accuracy. A hardware colorimeter reads the actual output and builds a correction profile; without one, a tint you spot on the white field is a reason to investigate, not a measured fault.
Display Brightness in Nits and Luminance
Screen brightness is specified in nits, which is the same unit as candelas per square meter. A white screen lets you compare luminance between areas by eye, but only a meter can tell you whether the display reaches its rated peak.
Other Uses for a Full White Screen
Off duty, a full white screen still earns its keep: the same white page works as a light or a backdrop. Since it is a white screen online, a blank white screen is ready on any device the moment you open the white screen tool.
A White Screen as a Light Source for Video Calls
Placed in front of you, the display becomes a soft fill light for video calls, which helps when window lighting is poor. As a light source it beats nothing, though it is no match for studio lighting, and long sessions at full brightness can cause eye strain. Think of it as a white light background, not a lamp.
Product Photography and Tracing
For small-item product photography, a tablet running the white screen gives a clean backdrop with even lighting, and laid flat it works as a makeshift lightbox for tracing thin paper.
Download a White Screen Image
If you need a pure white screen offline, a white screen image at 1080p or 4K serves as a wallpaper or slide. For testing, though, a downloaded image is weaker than the live fullscreen white screen, because image viewers add borders and toolbars. Keep a blank screen file handy only for jobs that need one.
Frequently Asked Questions
- How do I make my whole screen white?
- Click the white preview to enter fullscreen, or press F11 on a desktop browser. Press Esc to leave. On a phone or tablet, tap the fullscreen icon and lock rotation so the white field fills every edge.
- Can a white screen test find dead pixels?
- Yes. A dead pixel shows as a black dot on white. Confirm it by switching to red, green and blue: a dot that stays black on all of them is dead, while one that disappears on a single color is stuck.
- How many dead pixels are acceptable?
- It depends on the maker's pixel policy. Many still follow the old ISO 13406-2 Class II limit of 2 bright and 2 dark faults per million pixels, which works out to about 7 of each on a 2560 × 1440 screen. A retailer's return window is usually more generous, so test as soon as the screen arrives.
- Can this tool fix a dead or stuck pixel?
- No. It only displays colors so you can find faults. Stuck pixels sometimes respond to pixel-fixing software that flashes rapid colors; dead pixels are usually permanent and fall under warranty or return rules.
- Why does my white screen look yellow or blue?
- Night Light and other eye-comfort modes, the color temperature setting, ambient light and viewing angle all shift how white looks. Turn those modes off before judging the screen's own white point and uniformity.
- Should I use a white or black screen for backlight bleed?
- Use black. White maps dust, dead pixels and uneven brightness, but light leaking from the edges of an LCD is easiest to see on a black screen in a dark room.
- Can a white screen measure brightness or color accuracy?
- No. It lets you compare areas by eye. Brightness in nits and true color accuracy need a hardware colorimeter or light meter.
- Does a white screen use more power?
- On OLED screens, yes: every pixel lights at full strength, so power use and heat rise. Keep test sessions short and lower the brightness when you use the white screen as a light source.