Must-Do Screen Tests: Dead Pixels, Backlight Bleed & the ISO 13406-2 Standard

GearLab Hardware Column・Last updated: January 25, 2025

Excited about your new monitor? Don't throw away the box yet! Panel manufacturing defects aren't a rare exception — they're a normal part of the industry. The most important thing to do within your 7-day return window is a "Screen Check." Once the box is gone and the return window closes, any issue you find later has to go through warranty instead, and you might even be told it's "within normal range" and non-returnable.

Besides walking you through a standard inspection with GearLab, this article explains how manufacturers actually define that "normal range" and why some defects simply aren't eligible for a swap — so you can make an efficient decision the moment your new monitor arrives.

1. Why You Must Inspect Within the Return Window

An LCD panel is a precision product built from millions, sometimes tens of millions, of transistors and liquid crystal cells — a 100% manufacturing yield simply isn't realistic. That's why panel makers and downstream brands alike follow international standards to define an "acceptable number of defects," rather than demanding every panel leave the factory flawless — that kind of standard would show up directly in the price, if such units were even available at all.

This creates a real-world consequence: as long as the defect count is within spec, support may well tell you it's "within normal range" and decline a return, even with photo evidence. So the golden window to inspect is the moment you receive the monitor — not two or three months down the line. Most platforms only give you a 7-day return window; miss it, and your only path left is warranty, which is typically even more lenient than return policies.

2. Pixel Defects Explained: Bright, Dark & Sub-pixel Faults

Every "pixel" is actually made of three "sub-pixels" — red, green, and blue. A failure in the transistor or driving circuit of any of them can produce a different type of defect:

• Bright / Hot Pixel: Fixed at a certain color (usually white, sometimes a single color) regardless of what's on screen. Easiest to spot on a black background.
• Dark / Dead Pixel: Permanently black, unresponsive to any background color. Easiest to spot on a white or bright background.
• Stuck Sub-pixel: Only one of the three sub-pixels fails (e.g., the green one stuck on) — from a distance it might just look like an "off" color, not solid black or white, so you need the matching single-color screen (red/green/blue) to confirm it.

Dark pixels are the trickiest: they're barely noticeable on dark game scenes or wallpapers, and many people don't discover one until months in.

3. The ISO 13406-2 Pixel Fault Standard

"How many defects count as normal?" Most panel makers and brands answer this by following ISO 13406-2, an international standard originally about ergonomic requirements for flat panel displays. It groups defects into classes — the higher the class, the more defects are tolerated:

"Per million pixels" means the tolerance scales with resolution. Take a 27" 1440p monitor at roughly 3.69 million pixels as an example: under Class II, it theoretically takes 7 or more bright or dark pixels before it's even considered defective — far more lenient than most people assume "even one pixel should qualify for a return."

* ISO 13406-2 is a commonly referenced guideline, not a mandatory regulation, and actual return/warranty policies vary by brand — some premium lines (like certain professional color-grading monitors) advertise a "zero bright pixel guarantee," but that's usually limited to bright pixels only, for a limited period after purchase, and doesn't necessarily cover dark pixels or sub-pixel faults. Always check the specific brand and product line's official warranty terms before buying, rather than assuming the generic numbers here apply.

4. Interactive Demo: Where Do Defects Hide on Each Color?

This small demo recreates exactly why you need to cycle through five colors: there's a fixed white "bright pixel" and a fixed black "dark pixel" in the middle of the screen. Click a color swatch to change the background, and you'll see the same defect become completely invisible on certain backgrounds — that's exactly why checking only one color makes you miss defects.

* The bright/dark pixels in this demo are fixed for illustration; on a real screen, defects appear at random positions — which is exactly why you scan the whole screen instead of just the center.

5. Backlight Bleed vs. IPS Glow

This is mainly an IPS-panel issue. In a dark room with a full black screen, you may see whitish or yellowish glow near the edges or corners — but this actually covers two frequently confused phenomena:

• IPS Glow: An inherent physical trait of IPS technology — viewed off-axis or from an angle on a black screen, there's a uniform hazy grayish-white glow that gets more visible at wider angles and nearly disappears when viewed head-on. Every IPS panel has this to some degree; it's not a defect.
• Backlight Bleed: An assembly-related defect caused by tolerances in how the panel meets the backlight module, or bezel screws torqued too tight. It shows up as an uneven bright patch concentrated in one or two specific corners or edges, visible even head-on, rather than evenly distributed across all four corners.

The comparison below places both side by side: on the left, four corners glow evenly and symmetrically — normal IPS Glow. On the right, there's a clearly uneven bright patch in the top-right corner — the kind of backlight bleed worth flagging.

* VA and OLED panels don't bleed for quite the same reasons (OLED is self-emissive, so it has no backlight to leak in the first place, though it can show other uneven-emission issues). This section uses the most common case, IPS, as the example.

6. The Complete Inspection Procedure

1. Clean the screen surface: Remove dust, fingerprints, or leftover packaging residue so you don't mistake grime for a defect.
2. Turn off room lights: The darker, the better — ambient light seriously affects how well you can judge brightness differences, especially for backlight bleed.
3. Check at two brightness levels: Run through the test once at default brightness, then again after lowering it (e.g., to 20–30%) — backlight bleed is usually more visible at lower brightness.
4. Open GearLab's Dead Pixel Tool: Cycle through full-screen black, white, red, green, and blue.
5. On an OLED, add a burn-in check: Especially for used or display units. Burn-in doesn't show on black, so use the gray and single-color fields in the OLED Burn-in Check and look for fixed darker shapes like the taskbar or icons.
6. Scan by zone, not at a glance: From about 30cm away, mentally divide the screen into a 3×3 grid (or finer) and check each zone in turn, paying special attention to the corners and edges — bleed is almost always at the edges, while pixel defects can appear anywhere.
7. Recheck bleed from an angle: After the head-on check, view the full black screen from a slight angle. If the glow's shape and extent barely change and it's still concentrated in the same small area, it's more likely bleed than plain IPS Glow.

FAQ

I found one bright pixel — can I demand a return?

Depends on the platform and brand's policy. Under ISO 13406-2 Class II, a single bright pixel is usually still within tolerance and doesn't count as "defective." But if you're still inside a no-questions-asked return window, you can often return it anyway even without meeting the defect threshold — it just gets processed as a standard return rather than a defective-item return, which may affect who pays return shipping. Check your specific retailer's actual terms first.

Why can a monitor advertise a "zero bright pixel guarantee" and still have dark pixels?

Because most zero-bright-pixel guarantees only cover "Type 1" (bright) defects — the type most noticeable on bright content and in everyday use. Dark pixels and sub-pixel faults aren't necessarily included. Before buying, read the warranty text carefully: "zero defects" and "zero bright pixels" are very different promises.

Does backlight bleed get worse over time?

Mild bleed is usually caused by assembly tolerances and won't spontaneously worsen with normal long-term use. But if the monitor has been impacted, squeezed, or has loosened bezel screws, that can genuinely cause new bleed to appear or existing bleed to spread.

Can a phone photo prove my monitor has a defect or bleed?

It's useful as supporting documentation, but a phone camera's dynamic range, white balance, and the screen itself all interact in ways that often make bleed look far more dramatic — or far less — than what your eyes actually see. Most support teams will still want to test the physical unit themselves; photos are mainly there to document the moment you filed the claim.