Pixels

LCD Monitors and Faulty Pixels

LCD monitors are subject to a phenomenon where a dot on the screen is permanently stuck on or off. The result is a small point of either red, green or blue light or a small black point resembling a period [.] on the screen. In most cases, these individual spots go unnoticed.

What is a Pixel?

LCD monitors are made up of a fixed array of cells. Each cell has a single red, blue and green sub-pixel. Three sub-pixels make up a single pixel. A typical LCD monitor has 1280 x 1024 pixels. Since each pixel has three sub pixels that equates to approximately 3.9 million sub-pixels. Given the large number of sub-pixels per monitor the odds of finding a faulty sub-pixel are high. While faulty sub-pixels are common, a faulty pixel (three adjacent sub-pixels) is an extremely rare occurrence. Faulty sub-pixels typically happen during the manufacturing process. While they can fail in the field, this is also extremely rare.

What is Acceptable?

ISO9241-30x:2008 is the International Standard for the image quality of flat panel LCD monitors. 9241-30x:2008 covers key issues related to the quality of an LCD monitor including pixel defects.

Elo maintains high quality standards in its flat-panel touch monitors and has selected criteria based on the International Organization for Standardization (ISO) 9241-30x:2008 specification, which defines standard measurements of pixel defects. Elo LCD touchmonitors meet and, in most cases exceed, the ISO9241-30x:2008 Class 2 requirements for pixel defects noted in this table:

A Class 2 display allows 2 type 1 and 2 type 2 faults per million pixels. There are 5 type 3 sub-pixel faults (most common type) allowed per million pixels. The monitor examples below show the allowable number of fault pixels and sub-pixels.

What Does This Mean to the Customer?

Use this table, based on the ISO9241-30x:2008 specification, as a guide for assessing pixel defects. If any of the criteria above are exceeded, this validates a warranty claim.

Video Card and Pixel Faults

The system's video card can also be responsible for apparent faulty pixels or sub pixels. A faulty memory cell in the video graphics card can exhibit a phenomenon that looks like a faulty pixel or sub pixel on the LCD screen. To check for this, simply change the resolution of the system or hook the monitor to another system. The video graphic card is at fault if the faulty pixel moves or goes away.

Image Sticking

What is Image Sticking? What Causes Image Sticking?

Image persistence, image burn-in, and image sticking are terms used to describe LCD image retention. LCD image retention occurs when a fixed pattern is displayed over a prolonged period of time. The fixed pattern causes a parasitic capacitance build up within the LCD component, which prevents the liquid crystal molecules from returning to their normal relaxed state.

All LCDs/CRTs and color plasma displays are susceptible to image retention, at varying degrees. Phosphor based display devices, such as CRTs and color plasma displays are most susceptible, and image retention on phosphor based devices is often irreversible. Transmissive devices, such as LCDs are less susceptible, and in most cases LCD image retention can be reversed.

The rate of image sticking depends on the image pattern, duration of fixed image, the temperature, and production variations. Likewise, the rate of diffusion of the image sticking (recovery time) also depends on these factors.

What Can Be Done about It?

The best way to avoid image burn-in is to limit the amount of static content on the display. Image sticking may be avoided by turning the display off periodically for a period of time between 24 to 48 hours.

To reduce the possibility of image retention, we recommend:

• Displaying alternating black/white images for 48 to 72 hours
• Power down the unit for a period of time (minimum 24 to 48 hours)
• Use a screen saver when the touchmonitor is not in use

Image retention caused by static (non-moving) images displayed for lengthy periods (image burn-in) is not covered under Elo warranty.