Last month, we reviewed the latest ROG Swift gaming monitor from Asus, the PG279Q. It’s a premium 27-inch display with an AHVA panel, G-Sync, ULMB and a max refresh rate of 165 Hz with overclock. It impressed us enough to earn an Editor Recommended Award, but all was not perfect with our sample. In the screen uniformity tests, we found some backlight bleed (aka "IPS glow"), in the lower-right zone of the screen.
Our test measures nine areas of the screen for luminance. The outer zones are compared to the center one in order to derive a percentage variation. That means lower numbers are better. In our experience, any monitor scoring under 10 percent for either the full white or full black field test has no visible variations in light output. To the eye, it will appear to render a smooth and uniform tone from edge to edge.
Often a monitor will show one area that is a little hot in the black field test. If we can see it, the result is likely to be over 10 percent. In the case of the PG279Q sample, we measured a value of 17.58 percent, which is higher than average. If we had removed the hot zone from our calculations, the result would have been 12.62 percent, which is a barely visible situation.
So what does it all mean? In dark material, you will likely see a hotspot artifact, and it may or may not be distracting depending on the quality of your particular sample and the particular content you’re viewing. The issue is not an isolated one, and many users have reported visible light bleed on their PG279Qs. Fortunately for purchasers of the early production run, Asus is providing a solution by replacing defective panels.
This phenomenon is not that unusual among all types of LCD monitors. It’s caused by tiny variations in the gap between the first two screen layers. You’ve all seen what happens when you apply a bit of pressure to the screen with your finger: A glowing spot appears underneath. What you’re seeing is displacement of the crystals. Or in other words, the crystals become disoriented and allow more light through. This same pressure can be exerted by the anti-glare layer, causing a permanent hotspot. It’s more common in monitors that use a tight layer gap for clarity’s sake.
Manufacturers have to walk several thin lines with a mass-produced product. A tighter layer gap means a clearer picture, but it also means more panels will exhibit light bleed, because even the tiniest variation in flatness can cause the anomaly. Opening up the gap means fewer panels are thrown away, but it also reduces picture quality. Finding that happy medium is a challenge when you’re already selling displays at razor-thin profit margins.
We recommend inspecting any monitor thoroughly before committing, especially when you order it by mail. Light bleed can happen to any panel type – TN, IPS or VA, and their different variations. It all depends on how tight the layer gap is and what quality control measures have been taken to weed out defective parts before shipment. In the case of the PG279Q, Asus is maintaining its status as a premium display maker by taking care of dissatisfied customers.