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Backlight Bleed Test

Click anywhere or press any key to start. For best results, test in a completely dark room at maximum display brightness.

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About

Backlight bleed occurs when light from an LCD panel's edge-lit or direct-lit backlight escapes around the bezel, creating bright spots or uneven luminance - most visible on dark backgrounds at brightness levels above 80%. IPS glow, a related but distinct phenomenon, appears as warm white or yellowish haze in corners and shifts with viewing angle; it is inherent to In-Plane Switching technology and cannot be eliminated by panel replacement. Both defects reduce effective contrast ratio, which matters critically for color-grading workflows where deviations above 5% luminance uniformity violate ISO 3664 viewing conditions. This tool renders pixel-perfect solid fills via the Canvas API - no CSS backgrounds, no image compression - so every photon your panel emits is accounted for.

To get accurate results, perform the test in a completely dark room with your display at maximum brightness. The tool cycles through pure black (R=0, G=0, B=0), pure white, and primary/secondary colors. Black reveals backlight bleed and IPS glow. Solid primaries expose dead or stuck pixels. Note: this tool cannot distinguish manufacturing defects from temporary image retention on OLED panels - persistence testing requires sustained display times exceeding 10 minutes per pattern.

Formulas

Luminance uniformity is quantified as the ratio of minimum to maximum luminance measured across a grid of points on the panel surface. The ISO 3664:2009 standard for graphic arts viewing requires uniformity above 75%.

U = L_minL_max × 100%

Where U = luminance uniformity percentage, L_min = lowest luminance reading in cd/m², and L_max = highest luminance reading in cd/m². A perfectly uniform panel yields U = 100%. Backlight bleed effectively increases L_max locally while L_min remains at the panel's native black level, thus reducing U.

Perceived contrast ratio at any given screen region is:

CR = L_whiteL_black + L_bleed

Where L_bleed = luminance contribution from backlight bleed at that point. As L_bleed increases, the effective contrast ratio drops. A panel rated at 1000:1 static contrast with bleed adding 0.5 cd/m² to a native black of 0.3 cd/m² yields effective CR of approximately 375:1 in the affected region.

Reference Data

Defect Type	Appearance	Affected Panels	Viewing Angle Dependent	Fixable	Typical Location	Test Color
Backlight Bleed	Bright patches on dark screen	All LCD (TN, VA, IPS)	No	Sometimes (pressure fix)	Edges, corners	Black
IPS Glow	Warm white/yellow haze	IPS / PLS only	Yes	No (inherent to tech)	Corners	Black
Dead Pixel	Permanently dark dot	All LCD & OLED	No	No	Anywhere	White, Red, Green, Blue
Stuck Pixel	Permanently lit single color	All LCD	No	Sometimes (pixel exerciser)	Anywhere	Black, complementary colors
Clouding (Mura)	Broad uneven brightness areas	VA, IPS	Slightly	No	Center, large areas	Gray (50%)
Flashlighting	Bright glow from extreme corners	Edge-lit LCD	No	No	Extreme corners	Black
Banding (Gradient)	Visible steps in smooth gradients	8-bit, 6-bit+FRC panels	No	No (panel limitation)	Across gradient	Gray gradient
Image Retention	Ghost of previous image	IPS, OLED	No	Yes (temporary)	Where static content was	Gray
Uniformity Error	Brightness varies >10%	All panels	No	No	Quadrant-based	White, Gray
Color Shift	Hue changes at off-axis angles	TN (worst), VA	Yes	No	Top/bottom on TN	White, Red
Scanlines	Faint horizontal lines	PWM-dimmed panels	No	No (raise brightness)	Full screen	Gray
Pixel Inversion	Checkerboard flicker	Defective LCD driver	No	No (hardware fault)	Full screen	Checkerboard pattern

Frequently Asked Questions

Change your viewing angle. IPS glow shifts position and intensity as you move your head - it follows the viewer. Backlight bleed remains fixed in the same physical location on the panel regardless of your viewing angle. On a black test screen, note which bright areas move with you (IPS glow) and which stay put (bleed). Both are most visible at brightness above 80%.

Test at maximum brightness first - this is the worst-case scenario and reveals all defects. Then reduce to your normal working brightness. Many backlight bleed spots become invisible below 50% brightness. If bleed is only visible at maximum brightness levels you never use, it is functionally irrelevant for your workflow.

ISO 9241-307 defines pixel defect classes. Class I panels (medical, professional) allow zero defects. Class II (standard consumer monitors) allows up to 2 bright (stuck-on) pixels, 2 dark (dead) pixels, and 5 total sub-pixel defects. Most manufacturers follow their own stricter policies - Dell allows 1-6 depending on model tier, Samsung typically allows 0 on premium lines. Check your specific manufacturer's dead pixel policy.

Yes. Thermal cycling (repeated heating and cooling from power on/off) can cause the panel frame to warp slightly, increasing pressure irregularities on the light guide plate. Panels in hot environments or those left on continuously may develop new bleed points. Conversely, some users report bleed diminishing over the first 2-4 weeks as the panel settles (sometimes called 'break-in').

True 8-bit panels (not 6-bit+FRC) can display 256 discrete levels per channel. However, if your GPU output is compressed (e.g., YCbCr 4:2:0 chroma subsampling over HDMI) or limited-range RGB is sent to a full-range panel, quantization artifacts appear as visible banding. Ensure your GPU is outputting full RGB range (0-255) at the panel's native resolution with no chroma subsampling.

Partially. OLED panels have per-pixel illumination, so backlight bleed does not exist by design. However, this tool is still useful for OLED dead pixel detection (use white and primary color screens) and uniformity testing (gray screens reveal brightness variations across the organic layer). For OLED burn-in testing, you would need sustained static images displayed for extended periods, which this tool does not enforce.