Screens have millions of pixels, which each have a surface area of less than a hundredth of a square millimeter. These elements may have defects, which are expressed by them being constantly lit or unlit. Visibility is fundamentally dependent on the surrounding area. For example, lit elements are almost invisible in a bright environment. Each LCD screen is unique in terms of pixel errors. To give you a clear statement about what frequency of pixel errors EIZO deems tolerable, EIZO screen models are tested according to internationally recognized standards. On average the actual levels are in fact far below the tolerances across all of the devices. LCD modules that do not meet these requirements are not used at EIZO.  Depending on the model, EIZO monitors have a zero pixel error guarantee for completely illuminated sub-pixels (partial pixels ISO 9241-307). Valid: six months from the purchase date.