Just bought a new monitor? Considering a used phone? Need to verify your TV is working correctly? Testing your display properly can save you hundreds of dollars by catching defects before the return window closes or revealing issues before you buy.

I've tested hundreds of displays over the years—from budget monitors to flagship OLED TVs. Most people skip testing entirely, then discover dead pixels or backlight bleed weeks later when it's too late to return. This guide shows you exactly how to test any display, what results mean, and when you should demand a replacement.

This takes about 15-30 minutes for a thorough test. Grab a clean microfiber cloth and let's start.

Before You Start: Testing Environment Setup

The environment affects what you can see. Get this right before testing anything:

Clean your screen first:

Use a microfiber cloth (slightly damp if needed)
Dust and fingerprints look like dead pixels from a distance
Wait for the screen to completely dry
I've seen people "find" 20 dead pixels that were actually just dust

Control your lighting:

Test in normal room lighting first (baseline)
Then test in complete darkness (reveals backlight bleed)
Then test in bright sunlight/office lighting (reveals screen uniformity issues)
Different defects show up in different lighting

Screen settings:

Set brightness to 100% for backlight bleed testing
Set to 50% for dead pixel testing (easier on eyes, still effective)
Disable auto-brightness
Turn off blue light filters or night mode
Disable HDR for baseline testing

Use fullscreen mode:

Press F or F11 in most browsers
Essential for accurate testing
UI elements hide defects

Takes 5 minutes to set up properly. Worth it.

Test 1: Dead Pixel Detection (Most Critical)

Dead pixels are your #1 concern. They're permanent and can't be fixed. Most manufacturers allow 3-5 dead pixels before replacement, so catching them early matters.

What Are Dead Pixels?

Dead pixel: Completely black. The pixel is off and won't turn on. Stuck pixel: Stuck on red, green, or blue. Sometimes fixable. Hot pixel: Always white. Rare, but annoying.

How to Test for Dead Pixels

Step 1: Pure white screen

Go to our free testing tool
Select "White Screen"
Enter fullscreen mode (F or F11)
Slowly scan the entire screen in a grid pattern
Look for tiny black dots

Move your eyes slowly. Don't rush this part. Dead pixels are tiny—about 0.2mm on a 27" monitor.

Step 2: Pure black screen

Switch to "Black Screen"
Turn off room lights
Scan for colored dots or bright pixels
Stuck pixels show up as red, green, blue, or white dots

Step 3: Primary colors

Test pure red screen
Test pure green screen
Test pure blue screen
Each color reveals different stuck sub-pixels

Step 4: Document what you find

Take photos with your phone (tough to capture, but try)
Note the exact location (e.g., "2 inches from top-left corner")
Count total dead vs stuck pixels
Check manufacturer's dead pixel policy

Interpreting Dead Pixel Results

0 dead pixels: Perfect. Keep it.

1-3 dead pixels:

Check manufacturer policy
Premium brands (Apple, LG UltraFine): Usually replace for 1 pixel
Budget brands: Often allow 3-5 pixels
Location matters: Center screen is worse than edge

4+ dead pixels: Almost always grounds for replacement.

Pixel clusters (3+ adjacent pixels): Usually qualifies for replacement regardless of manufacturer policy.

Can You Fix Stuck Pixels?

Sometimes. Dead pixels (completely black) can't be fixed. Stuck pixels (colored) might respond to:

Pixel cycling:

Use our rapid color cycle mode
Run for 30-60 minutes
Cycles through all colors rapidly
Forces the pixel through state changes

Success rate is maybe 30-40%. Worth trying before returning if it's just outside the return window.

Test 2: Backlight Bleed and Light Leakage

LCD monitors use backlights. Sometimes light "leaks" around the edges—that's backlight bleed. It's normal to some degree, but excessive bleed is a defect.

What's Normal vs Defective?

Normal: Slight glow in corners visible only in a completely dark room on a pure black screen at 100% brightness.

Borderline: Noticeable glow on edges in normal lighting, or covering more than 1 inch from edges.

Defective: Bright spots or bands visible in normal room lighting, or bleed covering significant portions of the screen.

OLED exception: OLED displays should have ZERO backlight bleed (they don't use backlights). If you see glow on an OLED, something's wrong.

How to Test Backlight Bleed

Step 1: Environment

Turn off all room lights
Close curtains (complete darkness)
Let your eyes adjust for 2-3 minutes

Step 2: Display setup

Set brightness to 100%
Display pure black screen (use our tool)
Enter fullscreen mode
Sit at your normal viewing distance

Step 3: Observe

Look at all four corners
Check all four edges
Note any bright spots or clouding
Move your viewing angle (IPS glow changes with angle, bleed doesn't)

Step 4: Test at 50% brightness

Reduce brightness to 50%
Bleed should decrease significantly
If it doesn't change, it might be a different issue

IPS Glow vs Backlight Bleed

People confuse these:

IPS Glow:

Whitish/silvery glow at angles
Changes when you move your head
Normal on IPS panels
More visible at higher brightness
Not a defect

Backlight Bleed:

Yellowish or white light from edges
Doesn't change with viewing angle
Same brightness from all positions
Stays consistent as you move
Can be a defect if excessive

Test by moving your head left and right. If the glow moves or changes, that's IPS glow. If it stays in the same spot, that's bleed.

When to Return for Backlight Bleed

Return if:

Visible in normal room lighting
Covers more than 2 inches from edges
Bright spots in the center of the screen
Significantly affects dark content viewing
You paid premium price (expect better QC)

Keep if:

Only visible in complete darkness at 100% brightness
Minor corner glow
Doesn't bother you during normal use
Budget monitor (some bleed is expected)

Test 3: Screen Uniformity (Dirty Screen Effect)

Uniformity issues cause uneven brightness or color across the screen. Called "dirty screen effect" because it looks like the screen is dirty even when clean.

How to Test Screen Uniformity

Step 1: Gray uniformity

Display 50% gray (RGB 128, 128, 128)
Use our custom color selector or gray screen
Fullscreen mode
Look for darker or lighter patches

This is the most revealing test. Gray shows uniformity problems clearly.

Step 2: Color uniformity

Test pure red screen
Test pure green screen
Test pure blue screen
Look for tinting (e.g., one side looks pinker than the other)

Step 3: Test angles

View from directly in front (reference)
Move your head left and right
Move up and down
IPS panels should maintain color, TN panels will shift

Step 4: Real-world test

Open a large white document (Google Docs, blank page)
Open a large gray image
Scroll slowly and watch for brightness shifts

Interpreting Uniformity Results

Perfect uniformity: Rare. Even expensive monitors have slight variations.

Acceptable: Minor brightness variations (5-10%) visible only on pure gray. Not noticeable in normal use.

Poor uniformity: Obvious patches, vertical/horizontal bands, or "dirty" appearance on solid colors. Affects productivity work.

Very poor: Looks like water stains or clouds on gray/white screens. Return it.

Special Case: Vertical Banding

Vertical banding (lighter/darker vertical stripes) is particularly annoying because it shows up on documents and spreadsheets. If you see clear vertical bands on gray, that's grounds for return even if it's "within spec."

Test 4: OLED Burn-In Detection

OLED displays (iPhone 12+, Samsung Galaxy, OLED TVs, newer laptops) can suffer from burn-in—permanent ghost images of static content.

How to Test for OLED Burn-In

Step 1: White screen test

Display pure white screen at 80% brightness
Look for faint shadows or outlines
Common burn-in sources:
- Status bar icons (phone)
- Navigation buttons (phone)
- News tickers (TV)
- Game UI elements (monitor)

Step 2: Gray screen test

Display 50% gray
Burn-in is often more visible on gray than white
Look for "ghosts" of app icons, keyboard, etc.

Step 3: Color shift test

Display pure colors (red, green, blue)
Look for patches that appear different in color intensity
Indicates uneven OLED degradation

When to Worry About Burn-In

Don't worry if:

Display is less than 1 year old and used normally
Very faint shadows only visible on pure white at max brightness
No visible burn-in during normal content

Consider replacement if:

Obvious ghosts visible on normal content
Display is under warranty
Burn-in developed quickly (manufacturing defect)

Accept if:

Display is 3+ years old and heavily used
Minor burn-in on a cheap/old OLED
Outside warranty period

Burn-in usually isn't covered by warranty (wear and tear), but early/severe burn-in might be.

Test 5: Color Accuracy (Basic Check)

Full color calibration requires expensive tools, but you can do basic checks with our free tool.

How to Test Color Accuracy

Step 1: Primary colors

Display pure red (RGB 255, 0, 0)
- Should be vibrant red, not orange or pink
Display pure green (RGB 0, 255, 0)
- Should be grass green, not yellow-green or teal
Display pure blue (RGB 0, 0, 255)
- Should be royal blue, not purple or cyan

Step 2: White balance

Display pure white (RGB 255, 255, 255)
Should be neutral white (not yellow, blue, or pink)
Compare to a known-good reference (phone, laptop, etc.)

Step 3: Black level

Display pure black (RGB 0, 0, 0)
Should be true black (not gray)
LCD monitors will show some glow in dark rooms (normal)
OLED should be completely black

Step 4: Gradient banding

Display a smooth gradient (black to white)
Should transition smoothly without visible bands
Banding indicates limited color depth or poor calibration

Interpreting Color Results

Looks good: Colors appear vibrant, white is neutral, no obvious issues. For most users, this is enough.

Colors look washed out: Might need to adjust saturation settings or enable sRGB mode on wide-gamut monitors.

Colors look oversaturated: Disable "vivid" or "dynamic" modes. Enable sRGB mode if available.

White looks yellow: Color temperature too warm (usually 5000K-6000K). Increase to 6500K.

White looks blue: Color temperature too cool (usually 7500K+). Decrease to 6500K.

Complete Testing Checklist

Use this for new purchases, used buys, or periodic checks:

Pre-purchase inspection (if viewing in person):

[ ] Clean screen with provided cloth
[ ] Check for visible scratches or damage
[ ] Test all inputs work (HDMI, DisplayPort, etc.)
[ ] Run dead pixel test with phone (show white, black screens)
[ ] Check backlight bleed in store (if they'll dim lights)

New monitor within return period (do this immediately):

[ ] Clean screen thoroughly
[ ] Dead pixel test (white, black, RGB screens)
[ ] Backlight bleed test (dark room, 100% brightness)
[ ] Screen uniformity test (gray screen, normal lighting)
[ ] Color accuracy check (primary colors, white balance)
[ ] Physical inspection (no scratches, stand works, buttons functional)
[ ] Test at different brightness levels (25%, 50%, 75%, 100%)
[ ] Run for 24 hours (some issues develop after warm-up)

Used display purchase:

[ ] All of the above
[ ] Plus: Check for OLED burn-in
[ ] Plus: Test multiple video inputs
[ ] Plus: Check for firmware update availability
[ ] Plus: Verify warranty status (if applicable)

Annual/periodic check (for existing displays):

[ ] Dead pixel test (new pixels can fail over time)
[ ] OLED burn-in check (if OLED)
[ ] Color accuracy drift (colors fade over years)
[ ] Clean screen and chassis

How to Document Defects for Returns

If you find a defect and need to return or exchange:

1. Take clear photos/videos:

Use your phone camera
For dead pixels: Macro mode if available
For backlight bleed: Camera shows it better than eyes sometimes
Take photos from normal viewing distance and close-up

2. Write down specifics:

Exact location of defects
Count of dead pixels
Severity (visible in normal use or only in testing)
When you discovered it

3. Check the policy:

Manufacturer's dead pixel policy (usually on website)
Retailer's return policy (Amazon, Best Buy have different rules)
Warranty coverage (what's included, what's not)

4. Be polite but firm:

"I found X dead pixels at this location..."
"The backlight bleed is excessive and visible during normal use..."
Reference the manufacturer's own standards if they push back

5. Know your rights:

Many regions have consumer protection laws
"Fit for purpose" laws cover severe defects
Credit card purchase protection might help

When Is a Defect Worth Returning?

Not every imperfection justifies a return. Here's my take after testing hundreds of displays:

Definitely return:

4+ dead pixels anywhere
1-2 dead pixels in the center third of the screen
Backlight bleed visible in normal lighting
Severe uniformity issues affecting productivity
OLED burn-in on a new display
Physical damage (scratches, cracks)

Probably return (depends on price/usage):

2-3 dead pixels at edges
Moderate backlight bleed (dark room only)
Noticeable uniformity issues on gray
Color accuracy way off with no fix via settings
You paid premium price (expect premium quality)

Probably keep:

1 dead pixel at screen edge
Minor IPS glow (normal)
Slight uniformity variations only visible on test patterns
Budget monitor with minor issues (expected at the price)

Definitely keep:

Zero dead pixels
Minimal backlight bleed (dark room, 100% brightness only)
Good uniformity
Colors look accurate

My rule: If the defect bothers you during normal use (not just testing), return it. You're paying good money for this screen—don't settle.

Professional Testing vs Home Testing

What we've covered here is home testing—sufficient for catching obvious defects and making return decisions. Professional testing involves:

Equipment you don't have:

Colorimeter (X-Rite, Datacolor) - $150-500
Spectrophotometer - $1,000+
Response time measurement tools
Light meter for luminance testing

Professional testing reveals:

Exact color gamut coverage (% of sRGB, DCI-P3, etc.)
Delta E color accuracy (lower is better, <2 is excellent)
Precise response times (GTG measurements)
Exact brightness uniformity percentages

When to get professional testing:

Professional photo/video editing
Critical color work
Expensive reference monitor ($1,000+)
Already own calibration equipment

For 95% of people, home testing is enough.

Common Testing Mistakes

I see these mistakes constantly:

Testing in the wrong environment:

Bright room makes backlight bleed invisible
Dirty screen looks like dead pixels
Wrong brightness settings

Expecting perfection:

No display is perfect
Even $2,000 monitors have minor imperfections
"Acceptable" varies by price point

Testing once and giving up:

Some issues develop after warm-up
Test after 24 hours of use
Dead pixels can appear later (rare, but happens)

Not checking the policy first:

Manufacturer's policy varies widely
Some allow 0 dead pixels, some allow 10
Know what you're entitled to before testing

Mistaking IPS glow for backlight bleed:

IPS glow is normal and changes with angle
Backlight bleed is static and can be a defect
Learn to tell the difference

Frequently Asked Questions

How long should I test a new monitor?

Minimum 15 minutes for a quick check (dead pixels, obvious bleed). Ideally, test within the first day, then again after 24 hours of use. Some issues only show up after the display warms up or settles in.

Is one dead pixel acceptable?

Depends on manufacturer policy and location. Most manufacturers allow 1-3 pixels. Premium brands (Apple, Dell UltraSharp) often replace for even one pixel. If it's in the center of your screen, push for replacement even if policy says it's acceptable.

Can I test my phone screen the same way?

Yes. Use our free testing tool on your phone's browser. Enter fullscreen mode and test for dead pixels, screen uniformity, and OLED burn-in. Phone screens are smaller, so dead pixels are even more annoying.

What if the store won't let me test before buying?

Buy from a retailer with a good return policy (Amazon, Best Buy, etc.). Test immediately at home. Many stores won't let you power on displays before purchase, so a flexible return policy is your safety net.

How do I test a TV from across the room?

TVs are viewed from farther away, so minor imperfections matter less. Focus on backlight bleed (very noticeable from a distance) and large dead pixel clusters. Single dead pixels are nearly invisible from 6-10 feet away.

Is backlight bleed worse on curved monitors?

Not inherently, but curved panels can show bleed differently. The curve can amplify corner bleed or make it less visible depending on viewing angle. Test both on-axis and at angles.

Do OLED monitors have backlight bleed?

No. OLED displays don't use backlights—each pixel produces its own light. If you see "bleed" on an OLED, it's either reflections, ambient light, or a defect. True blacks should be completely black.

Will dead pixels spread over time?

No. Dead pixels don't "spread" to nearby pixels. Each pixel fails independently. If you're seeing more dead pixels over time, they're separate failures, not spreading—but that might indicate a quality issue worth investigating.

Can heat or cold cause dead pixels during testing?

Extreme temperatures can cause temporary pixel issues. Test at normal room temperature (18-24°C / 65-75°F). If you just brought a monitor in from cold weather, let it warm up for 30 minutes first.

Related Resources

Display troubleshooting guides:

Windows Black Screen Fix - Startup and login black screen solutions
Laptop Black Screen Fixes - Laptop-specific hardware diagnostics
Computer Black Screen Checklist - Quick diagnostic flowchart

Testing tools and prevention:

Free Black Screen Tool - Our professional testing tool (all devices, no download)
OLED Burn-In Prevention - Protect your OLED investment
Best Monitor Testing Tools - Comparison of testing software and tools

Start Testing Your Display

Don't wait until it's too late. Whether you just bought a new monitor, considering a used one, or haven't tested in years, spending 15-30 minutes now can save you money and frustration later.

Use our free black screen testing tool to run all the tests mentioned in this guide—no download, works on any device, completely free.

Found a defect? Document it properly, check the return policy, and act before your window closes. Your eyes (and wallet) will thank you.

How to Test Your Display: Complete Step-by-Step Guide [2025]