LCD Screen Tester
Cycle through solid colors, grayscale shades, and a checkerboard pattern fullscreen to spot dead pixels, stuck pixels, and backlight uniformity problems. The bandwidth calculator calculates the signal bandwidth required for any resolution, refresh rate, colour depth, and chroma subsampling combination.
Click Start Full Screen Test to cycle through all test patterns, or use Prev/Next to jump straight to one. Press ESC to exit anytime.
Ever unboxed a brand-new monitor, notebook, or handset and wondered whether every single dot is performing exactly as it should? Your LCD screen tester gives you a definitive, web-based answer — revealing dead pixels, stuck pixels, backlight bleed, gradient banding, and touch dead zones in minutes, without installing a single app. Whether you're evaluating a fresh purchase, preparing a warranty return, or simply doing routine display diagnostics, the results you get here directly determine your next move.
How to Run Your LCD Screen Tester in Full-Screen Mode for Dead Pixel Detection
Getting the most accurate results from your dead pixel test starts with eliminating distractions. Before you begin, wipe the glass gently with a soft cloth to remove dust or smudges — even a small speck can mimic a dot fault and send you on a false hunt. Once the surface is clean, enter full screen mode so every point from edge to edge falls under inspection. Run the monitor color test to quickly spot colour banding, tinted grays, or warm/cool casts that indicate calibration drift.
Keyboard Shortcuts and Mouse Controls for Pixel Fault Detection
- Press F11 (Windows/Linux web browsers) to toggle full-screen mode. On macOS, use the browser's View menu or the green resize button.
- Click the left mouse button to advance to the next color field once you have finished scanning the current view.
- Press Space to show or hide the on-screen navigation bar without leaving the current test.
- Press Esc to exit fullscreen mode at any time and return to this page.
- Let your eyes accommodate to the luminance level for a few seconds on each field before declaring it clear — your visual system needs a moment to calibrate to a uniform field, which aids screen calibration judgment.
"A super fast tool to verify dead pixels on any monitor or screen, including tablets and mobile devices. I use it often without errors."
Running the LCD Test on Handsets and Tablets
On handsets and tablets the experience is fully touch-driven. Tap the full-screen button within the tool, or allow the Fullscreen API to engage automatically when you tap the first color field. If your web client does not support the API — a common fallback situation on older Android WebViews — the tool still fills the visible viewport so you can look carefully at every region of the unit. Swipe left or tap to change test fields, and make sure to check all areas including corners, which are most prone to light bleeding on edge-lit units. Everything stays in your browser — no data is sent to any server and nothing is stored, so your device information remains completely private.
Test Pattern and Baseline Screen Check Using the LCD Screen Tester
The opening test pattern is your baseline lcd test reference. It displays overlapping geometric shapes, fine frequency patterns, and color gradients simultaneously, letting you assess multiple dimensions of image quality before you isolate individual problems. Think of it as the overview frame: if anything looks wrong here, the subsequent single-color fields will pinpoint exactly what type of visual defect you are dealing with. Use the refresh rate tester after a driver update or refresh rate change to confirm the new setting is active.
Reading the Three Resolution Numbers — Pixel Size Calculator and LCD References
Below the pattern you will see three resolution numbers. Understanding what each means prevents misreading your results. These figures also serve as useful lcd references when comparing units side by side, and a pixel size calculator approach helps you gauge how fine the dot structure actually appears at your seating distance:
- Viewport resolution — the dot dimensions the rendering engine is currently using. This is what the image quality check actually fills. It is controlled by zoom level and OS scaling settings.
- Native screen resolution — the physical dot count of your hardware, reported by the operating system regardless of scaling.
- Device pixel ratio — the multiplier between logical CSS units and physical hardware dots, retrieved via
window.devicePixelRatio.
On a Retina display or any other high-DPI unit, the device ratio is typically 2× or 3×. That means a viewport of 1,440 × 900 logical units maps to 2,880 × 1,800 physical dots on the hardware. For an element inspection to be meaningful on these units you need to view the full-screen color fields from a short distance so individual dots remain visible. For lcd screens on desktop monitors running at 4K with 100 % OS scaling you will see a 1:1 ratio and every physical dot is directly exercised. For lcd screens on a notebook using fractional scaling, the viewport will be smaller than the native resolution, and you should treat the native figure as your reference when counting columns or rows of faults.
Dead and Stuck Pixel LCD Test — Checking Screen Quality Across Every Color Field
The core of any solid visual inspection is the series of solid, single-color full-screen fields. A dead pixel (sometimes called a dark dot or missing point) is one whose transistor has permanently failed — it stays black regardless of what color the unit tries to render. A bright dot is one whose sub-element components are locked open, continuously illuminated even when they should be off. Partial sub-element faults occur when only one of the three color channels inside a dot is stuck, producing a faint colored tint rather than a fully lit or fully dark spot. These are among the most common pixel defects found on both LCD and emissive technology surfaces, and they directly affect display quality.
Cycle Every Color in One Full-Screen Pass to Catch All Pixel Defects
The most efficient approach is a color cycle check: loop through all six color fields without skipping any. The table below maps each field to the specific category of fault it best exposes, along with what you are looking for — part of a thorough banding test and color-shift test routine to assess lcd pixels structure integrity.
| Color field | What it reveals |
|---|---|
| Black | Faults on black — any dot lit in color (a glowing point or always-on sub-element) is a stuck dot. Also reveals illumination leakage and clouding. |
| White | Faults on white — any dark dot indicates a missing point. Reveals any area where the light source fails to pass through the liquid crystal layer. |
| Red | Faults on red — a dark dot indicates a missing red sub-element; a cyan-lit dot (green + blue) shows a stuck red channel. |
| Green | Faults on green — a dark dot reveals a missing green sub-element; a magenta dot shows a stuck green channel. |
| Blue | Faults on blue — a dark dot reveals a missing blue sub-element; a yellow dot indicates a stuck blue channel that remains blue when neighboring dots switch off. |
| Gray | Mid-gray — mid-range luminance anomalies, subtle illumination unevenness, and partial sub-element faults invisible at full saturation become apparent during this gray tone evaluation. |
Gray Tone, Emissive Burn-In, and Sub-Element Fault Isolation
The gray tone field deserves special attention. Because it sits at roughly 50 % luminance, it can expose dot faults that hide at extremes — a sub-element stuck at a low value might blend into a black field but stand out clearly against mid-gray. It also reveals grayscale uniformity problems: if one half of the unit appears lighter than the other, your illumination or local dimming zone configuration may be uneven. This kind of check is essential for proper screen calibration.
For OLED surfaces — found in premium smartphones, high-end notebooks, and modern emissive units for computing — the black field is particularly important. Because each self-emitting dot generates its own light, a true black means the dot is fully off. Any lit point on the black field is unambiguously stuck. However, users of emissive technology should limit the duration of each solid-color pass to reduce burn-in risk. Running each field for 15–30 seconds is sufficient for a thorough scan. On an emissive surface, if you notice faint image remnants from previous content appearing on the white or gray fields, that is burn-in rather than a dot fault — a different (and currently irreversible) issue.
Worked example — stuck sub-element vs. missing dot: Imagine you are running the black field on a new monitor and you spot a bright red point. Because the field is all black and the point stays lit, you are looking at a stuck sub-element — specifically, the red channel of that dot is continuously illuminated. Switch to the white field: if the same location now appears white like the rest of the surface, you have confirmed it is not a dead pixel (which would appear dark on white). Switch to the red field: if the spot looks identical to its neighbours, the red sub-element is stuck open. Now switch to the green field: if a cyan dot appears in the same location, that further confirms only the red channel is locked on. Document the position, capture the evidence, and check your manufacturer's warranty policy — most brands require a minimum count of stuck or non-functioning dots (commonly five or more for office monitors and all-in-ones) before authorising a replacement.
Uniformity, Color Accuracy, and Gradient LCD Screen Tester Evaluation
Once you have cleared the solid-color fields, the lcd test continues with uniformity and gradient evaluation — the tests that separate a mediocre unit from an excellent one for photography, design, color grading, and medical imaging work. Checking screen quality at this stage reveals subtle issues that the solid-color pass cannot expose, including lights and shadows distribution across the surface.
Tell Backlight Bleed From a Viewing-Angle Gradient Artifact
Image uniformity problems come in several flavours that are easy to confuse. Load the uniform gray or dark gray field and dim the room lights to enhance contrast. Genuine backlight bleed — also called illumination leakage — appears as diffuse bright patches fixed in position, usually in corners or along edges, regardless of whether you are looking straight at the surface or from an angle. Clouding creates irregular lighter blobs across the centre. IPS glow is a silver-blue luminance halo visible only at steep off-axis positions; it vanishes when you return to a perpendicular angle, distinguishing it from true leakage. Move your head left and right during the uniformity check: if the bright area shifts or disappears, it is a viewing-angle gradient artifact from your technology — not a hardware defect. If it stays fixed, escalate to the manufacturer.
Worked example — notebook illumination leakage: A notebook user notices that the bottom-left corner of the screen looks noticeably lighter during dark scenes in films. They open the uniformity check and select a near-black field. The bright patch is clearly visible from directly in front of the surface and does not move when they tilt their head. Shifting the seating position makes no difference. This rules out a viewing-angle gradient and confirms genuine illumination leakage. They photograph the fault against the dark background and contact the manufacturer's support line, citing the uniformity result.
Levels, Gradients, and Color Distances — Bit-Depth and Color Reproduction
The gradient check pushes a smooth ramp from pure black (0) to pure white (255) across the full width of the surface. At a normal viewing distance, a healthy 8-bit unit should render this as a perfectly continuous transition with no visible banding — abrupt tone steps between adjacent shades. If you can see distinct bands or steps, your hardware may be limited to 6-bit color output (with dithering), or your OS color management settings may be clipping values. A banding test at this stage is the fastest way to confirm bit-depth limitations. This is also where a 10-bit unit genuinely differentiates itself from an 8-bit one: at 256 intervals, the 10-bit surface resolves steps that are invisible on 8-bit hardware. Enable the maximum interval count in the gradient settings and study the shadow end of the ramp — shadow clipping indicates your dynamic range settings are too aggressive. The Levels sub-test within the gamma section specifically targets highlight and shadow clipping for a dynamic range check, helping you identify whether the brightness slider in the system menu is set too high or too low.
The color distances check lets you create two adjacent color patch swatches and adjust their R G B values independently. The goal is to find the smallest difference — measured perceptually in delta-E style color distances — that your unit can render as two distinguishable swatches. Units with excellent color fidelity separate shades that cheaper alternatives merge into a single flat tone. This check is especially well-suited for a direct visual comparison between two units side by side, and it can reveal a color-shift test failure when one swatch unexpectedly blends into the other.
Sharpness, Viewing Angle, Gamma, and Response Time Check
A comprehensive evaluation goes beyond dots and uniformity. The remaining test modules assess the optical and electronic performance characteristics that determine whether your unit feels crisp, colour-stable, and lag-free during real use.
Speed (Units Per Second), Motion Blur, and the Panning Sequence
The response time test moves a pair of rectangles horizontally across the surface. You configure two key variables:
| Setting | Range | What it controls |
|---|---|---|
| Speed (units per second) | 480 – 3,840 | How fast the rectangles traverse the surface — higher speeds expose more motion blur |
| Distance (units) | 0 – 150 | Gap between the left rectangle and right rectangle; reduce until the trailing streak of the right rectangle overlaps the leading edge of the left |
| Background color | Custom RGB | Contrast between the rectangle color and background affects streak visibility |
| Font size (point) | 10 – 18 | Sets the label text inside each rectangle for text sharpness assessment during motion |
Set a speed units per second value that creates visible streak rectangles — typically 1,920 units/s is a good starting point for a 60 Hz unit. Then reduce the distance setting until the trailing smear of the right rectangle just overlaps the left rectangle's lower edge. The shorter the minimum distance at which they remain visually separate, the faster your hardware's dot response and the shorter its response time. Use this check to evaluate the effect of your overdrive setting: excessive overdrive often introduces inverse ghosting (a white halo ahead of moving objects) that is visible as a glowing leading edge ahead of the rectangles. You can also compare refresh rates by enabling high-refresh mode and rerunning the check — blur reduction improvements between 60 Hz and 144 Hz become immediately measurable.
The sport pan sequence scrolls a detailed photographic scene horizontally at a fixed rate, simulating a camera panning across a sporting event. Ghosting appears as duplicated edges trailing behind high-contrast objects. Any smearing in this sequence translates directly to reduced clarity during fast-paced gaming and action video. A thorough evaluation using the sport pan alongside the movement check gives you a complete picture of how dot response interacts with refresh rate to determine perceived sharpness. Running a second sport pan pass at a higher speed helps confirm whether the smearing is speed-dependent.
Left Rectangle, Right Rectangle, Distance Settings, and Gamma Value
The left rectangle serves as your stationary reference. The right rectangle moves at the configured speed. When you observe color banding or tonal breaks inside the rectangles themselves, that is a sign that your hardware's gamma value is miscalibrated — typically set too high or too low relative to the standard gamma 2.2 reference curve used for most content. Use the gamma slide to dial in the value where the test logo's grayscale blends most cleanly into the surrounding background. A correctly set gamma (2.2 for most content, 2.4 for darker environments) ensures mid-tone rendering accuracy across the full luminance range, which is critical for color management in design and photography workflows. Calibration hardware can confirm this reading, but the on-screen gamma slide provides a fast, free first check. The sharpness module complements this by verifying font rendering: choose a font size of 10 pt and look for halos or soft edges — signs of oversharpening in the image settings, or under-sharpening caused by suboptimal text smoothing in your OS.
The viewing angle check presents a set of circles and geometric shapes. Walk or tilt to an off-axis position and observe whether the circles remain round and the shapes retain their color stability. A circle distortion check reveals geometry errors. A color-shift test at the boundary angle — especially a red-to-yellow or blue-to-green shift on cheaper IPS or VA units — confirms that colour rendition is viewing-angle dependent rather than a calibration error at your default seating position. Luminance and dimming controls can be adjusted to keep results comparable across sessions, and studying the lights and shadows behavior at oblique angles helps distinguish panel technology limitations from genuine faults.
Touchscreen Test and Handset Full-Screen Check
The touchscreen test adapts to any size surface, covering handsets, tablets, Chromebooks, and any other touch device. It divides the active area into a grid of touch zones and tracks which squares have been activated — making it a straightforward tool for finding dead zones, edge responsiveness failures, and multi-touch inaccuracies.
How to Test Your Touch Surface Step by Step
- Start the test: tap Touch anywhere to initialise the grid. Each square begins blue.
- Slide your finger slowly across every square on the surface, covering all areas including all four edges and corners.
- Check for colour changes: each square that registers correctly turns orange (or your device's success colour). A square that remains blue even after you have touched it multiple times indicates that area has a problem — likely a dead zone in the touch digitiser.
- Check the far left edge: if a vertical strip along the left side remains blue despite repeated contact, you have found an unresponsive strip — document its width and position.
- Press the camera button to capture a screenshot of results before the grid resets. This captured image becomes your evidence for a warranty claim or a repair assessment.
- Test more aspects of your device — microphone, camera, and sensors — using the full device check available from the main menu.
Multi-Touch Point Verification on Handset, Tablet, and Chromebook
If the areas of touch work individually but you suspect a multipoint limitation, perform a touch at several points simultaneously — press five fingers flat onto the surface and verify that all five are tracked at once. Most modern smartphones register ten simultaneous touch points. A Chromebook touch surface typically supports ten points as well. If your device only registers two or three simultaneous contacts when the specification states more, the digitiser may be partially failed or damaged. On a tablet, schools and institutions issuing shared devices will find this especially useful: run the multi-touch check on every unit before distribution and again after collection to detect physical damage. Touch sensitivity issues near a cracked edge are a common failure mode that this check will expose as a persisting blue square even after repeated taps.
Worked example — unresponsive strip on a new handset: A user runs the touch surface check on their new handset and notices a narrow vertical strip of squares along the left edge remains blue after slide your finger has passed over them multiple times. They confirm the issue by tapping individual squares in that column — each time the square remains blue rather than turning orange to signal a successful contact. The check is not successful for that column. They capture the result, note the strip width (approximately 8 mm), and contact the retailer with the photographic evidence. The screen quality defect qualifies as a manufacturing fault under the device's warranty return policy, and a replacement unit is dispatched.
When the Fullscreen API does not engage on older web clients, the tool falls back to filling the viewport as completely as CSS allows — a mobile fullscreen fallback that works reliably on virtually all devices. Even without true OS-level fullscreen, the grid covers enough of the visible area to make the check valid. On an iPhone, tapping the Share icon and selecting Add to Home Screen launches the tool in standalone mode, which eliminates browser chrome and maximises the test surface. Everything stays in your browser — no data sent to any external server — so running this check on a school device or a corporate handset raises no privacy concerns.
Frequently Asked Questions About LCD Screen Testing
What is a dead pixel and how is it different from a stuck pixel?
A dead pixel has a transistor that has permanently failed, leaving it always black regardless of the image being displayed. A stuck dot is one whose sub-element components remain always-on, showing as a bright point in one or more colors. Both are types of pixel defects, but their appearance and potential fixes differ: some stuck dots respond to rapid cycling or gentle pressure techniques, while non-functioning dots rarely recover without a hardware replacement.
How many dead pixels does it take to qualify for a warranty return?
Manufacturer thresholds vary by product tier. Most consumer monitors and LCD surfaces require five or more faulty dots — or a single non-functioning dot within a specific zone — to qualify for replacement under standard warranty policies. Emissive technology manufacturers are often stricter, accepting even one or two non-functioning dots on a premium device. Always document faults with the color field checks and capture the results before contacting support.
Can this tool fix stuck pixels?
The rapid color cycle check can sometimes help fix stuck pixels by cycling the sub-element rapidly between on and off states. Leave the color cycle running on the affected area for several minutes. Results are not guaranteed, and this technique works far more reliably on stuck dots than on non-functioning ones.
Does the test work on OLED screens?
Yes. The tool works on any display technology — LCD, emissive, AMOLED, and Mini-LED. On an OLED surface, the black field check is especially revealing because each dot is self-emissive, so any lit point on a black background is unmistakably stuck. Limit each solid-color pass to 30 seconds on emissive surfaces to minimise burn-in risk during testing.
Why does my viewport resolution differ from my native screen resolution?
Your OS scaling setting and zoom level both affect the viewport. A high-DPI or Retina surface with 2× scaling shows a native resolution twice the viewport dimensions. The web client reports the scaling factor via window.devicePixelRatio. The visual quality check fills the logical viewport, not the physical dot grid, so on high-DPI surfaces you are testing logical units that each correspond to multiple physical dots.
What should I do if my touch screen doesn't pass the test?
First, clean the surface — oils and moisture on the glass can interfere with capacitive touch sensitivity. If after cleaning a touch surface still fails the check, reboot the device and rerun it. If specific squares remain blue consistently across multiple sessions, the digitiser has a hardware fault. Capture the result and contact your manufacturer or retailer. For a device under warranty, a touch digitiser failure typically qualifies for repair or full replacement.
Does everything really stay in my browser?
Yes — this is a fully client-side, web-based check. No dot data, resolution figures, or device information are transmitted to any external server. No data sent means you can safely run this on personal, corporate, or institutional devices. The tool requires only a standards-compliant web client to function.
Can I use this as a free online check before buying a used monitor?
Absolutely. Bring any laptop with a web client to the seller's location, open the tool, and run a full color cycle check through all six solid-color fields — it takes under two minutes. This is one of the most practical online checks you can run before committing to a second-hand purchase. Pair it with the uniformity check to assess illumination leakage and the response time module for ghosting.
Does the touchscreen test support multi-touch and how do I verify it?
Yes. After sliding across all squares to verify individual touch accuracy, place multiple fingers simultaneously on the surface to test multipoint touch. Check all areas including corners, where digitiser sensitivity is often reduced. If only some of your fingers register while others produce no orange response, the hardware's multi-touch layer has a capacity limitation or a localised fault.
"I used this free online screen test to check my new laptop before the return window closed — found two stuck dots in the top-right corner on the blue field. Returned it the same day and got a perfect replacement. Took less than three minutes total."
Display quality matters most when you push a unit to its limits — whether you are doing professional color work, gaming at high refresh rates, or just expecting every dot of a premium purchase to earn its place. Running a complete lcd test with this lcd screen tester the moment you unbox a new screen costs nothing and could save you weeks of dealing with a faulty unit you failed to notice within the return window. Bookmark this page, run it on every new screen, and check all areas — your evaluation is only as thorough as the tests you actually carry out.
Frequently Asked Questions
- What is the difference between a dead pixel and a stuck pixel?
- A dead pixel receives no power and appears permanently black on any background. A stuck pixel is trapped sending one color signal — often red, green, or blue — and stays that color regardless of what the screen displays. Stuck pixels are more common and sometimes recoverable; dead pixels usually are not.
- Does this test send any of my screen data anywhere?
- No. All calculations happen entirely in your browser using the values you enter. Nothing is transmitted to any server. Your screen resolution, defect count, and results stay completely local.
- How many dead pixels do I need to qualify for a warranty return?
- Most manufacturers follow the ISO 13406-2 standard. For Class II panels (typical consumer monitors), up to 2 fully dead pixels and up to 5 stuck pixels are considered acceptable. Some premium brands like EIZO offer zero-defect guarantees. Always check your specific manufacturer's dead pixel policy.
- Can this tool fix stuck pixels?
- This calculator identifies and scores defects — it does not fix them. Some stuck pixels can be recovered by rapidly cycling colors on screen using a dedicated pixel-fixing tool, or by gently massaging the affected area with a soft cloth while the screen is on. Dead pixels cannot be repaired.
- Does the test work on OLED screens, and is anything different?
- Yes, you can select OLED as your display type. OLED screens have individual self-emissive pixels, so dead pixels appear as black dots visible on any color. OLED is also susceptible to burn-in rather than backlight bleed, since there is no backlight. The scoring reflects these differences.
- What does each solid test color reveal?
- White reveals dark or dead pixels. Black reveals bright stuck pixels and backlight bleed. Red, green, and blue each expose stuck sub-pixels in those channels. Cyan, magenta, and yellow help identify sub-pixel defects that pure primary colors might miss.
- Why might a 'dead' pixel look alive on a high-DPI or Retina display?
- On Retina and high-DPI displays, the OS often renders at a lower logical resolution and upscales. A single hardware pixel defect may be invisible at normal viewing distance because surrounding pixels compensate visually. Testing at native resolution or zooming in closely helps reveal such defects.
- What is pixel density (PPI) and why does it matter for screen quality?
- PPI (pixels per inch) measures how many pixels are packed into each inch of screen area. Higher PPI means sharper, crisper images. For typical desktop viewing distances, 90–120 PPI is standard; laptops and phones benefit from 200+ PPI. Low PPI displays may show individual pixels visibly, affecting perceived quality.