The illustrated panel sits in a test fixture with its flexible printed circuit tails folded out, the stage at which a TFT screen is switched on and judged before it goes into a product. No panel with millions of sub-pixels comes out perfect, so each maker publishes the defects it accepts. Three such documents, from a display-module maker, a module distributor and an electronics distributor, show how differently the same defects are counted.
Covers the defect definitions, acceptance limits and inspection conditions for TFT LCD panels and modules: pixel (dot) defects, line defects, spots, lines and scratches, polarizer bubbles, uniformity, sampling and lot acceptance. Module interface, brightness, viewing angle and backlight selection are on the LCD module page (5449); backlight units on 6724; smart display modules with on-board controllers on 644; impact-rated touchscreens on 3982; medical-grade monitors on 9078. Instrument TFT screens built into power meters share the name and are outside this page.
CNFX editorial research · Sources checked October 13, 2026 · 3 sources
Bright dots, dark dots and clusters: three makers' limits
Velleman's information sheet defines a bright dot as a pixel or sub-pixel visible through a 5% neutral density filter, held parallel at 2.5 to 3 cm, on a black pattern, and a dark dot as one that appears dark on an RGB pattern. Riverdi counts bright sub-pixels on a black pattern and dark ones on red, green, blue and white.
Velleman counts adjacent dots toward the single-dot total as well. Riverdi classes pixel defects, line defects and flicker as major defects.
Velleman's example monitor has 1,280 × 1,040 = 1,331,200 pixels, about 4 million sub-pixels; nine dot defects is about 2.3 per million sub-pixels (Editorial calculation).
Defect
Velleman (monitor panels)
Riverdi (3.5–15.6 in modules)
Bright single dots
N ≤ 6
N ≤ 1 sub-pixel
Dark single dots
N ≤ 6
N ≤ 2 sub-pixels
Total dots
N ≤ 9
—
Two adjacent
≤ 3 pairs
Dark: N = 1; bright: not allowed
Three adjacent
≤ 2 sets
Dark: not allowed
Four adjacent
≤ 1 set
—
Spacing
Two bright dots ≥ 10 mm apart
—
Line defects
Not allowed
Vertical and horizontal not allowed; flicker not allowed
The Riverdi bright-pixel row is read from the PDF table layout (sub-pixel N ≤ 1, two adjacent not allowed); confirm against the current revision before quoting it in a purchase specification.
02
Spots, lines, scratches and bubbles: limits scale with size
Cosmetic defects are judged by size. Velleman and EastRising size a round defect as the average of its longest and shortest dimension; Riverdi scales its allowances with screen diagonal.
EastRising separates 'clear' spots and lines, whose shade and size do not change with the drive voltage, from 'unclear' ones that do, and allows larger unclear defects.
Velleman leaves mura, non-uniform brightness over the display area, to individual evaluation rather than a numeric limit; EastRising's uniformity ratio of 2 is the only numeric brightness-uniformity limit among the three.
How the panel is inspected and how lots are accepted
The same panel can pass or fail depending on light, distance and angle, so each document fixes them.
The three setups differ enough that a defect count is only meaningful with its conditions attached: Riverdi's light level is 2 to 4.3 times Velleman's (Editorial calculation from 1,000–1,300 lx against 300–500 lx).
EastRising defines a lot as one delivery to the customer and classes a functional failure as major and a cosmetic shortfall on a working unit as minor.
Condition
Velleman
Riverdi
EastRising
Viewing distance
"approximately 35 ~ 40 cm" (much closer for adjacent dots)
35–60 cm
Lamp at 100 mm
Angle
Normal to panel, ≤ 10° off
60° from front surface, vertical
Tilted 45°
Light
300–500 lx ambient
1,000–1,300 lx
20 W lamp
Climate
25 ± 5 °C, 60 ± 5% RH
15–25 °C, 25–65% RH
—
Sampling
—
100% (exceptions by quality department)
MIL-STD-105D, single, level II; AQL 0.4% major, 1.5% minor
Inspection time
—
6–10 s
—
04
What to agree with a TFT panel supplier
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Agree in writing which document applies: bright and dark dot limits including adjacent clusters and spacing, line defects, spot, line, scratch and bubble limits by size for your diagonal, uniformity limit and measuring points, inspection light, distance, angle and test patterns, sampling plan and AQL for major and minor defects, and whether a panel with defects inside the limits can be returned. Ask for the supplier's inspection standard with its revision number and a limit sample.
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
How many dead pixels are allowed on a TFT screen?
It depends on the maker's standard. Velleman's sheet allows up to 6 bright and 6 dark dots, 9 in total, with no line defects; Riverdi allows 1 bright and 2 dark sub-pixels on its modules. [1][2]
How is a bright dot defined?
Velleman defines it as a pixel or sub-pixel visible through a 5% neutral density filter held 2.5–3 cm from the screen while a black pattern is displayed. [1]
What AQL is used for TFT LCD modules?
EastRising's ER-TFT1.95-1 datasheet uses MIL-STD-105D single sampling, general level II, with AQL 0.4% for major and 1.5% for minor defects. [3]
Sources and what still needs a direct check
Sources checked 2026-10-13. A distributor's information sheet on display defects (Velleman), a display-module maker's aesthetic standard (Riverdi) and a TFT module datasheet with inspection criteria (EastRising).
