Introduction

Dark spots or patches may occasionally appear on some liquid crystal display (LCD) panels. This clouding phenomenon is recognized in the industry as YOGORE or "Mura", a Japanese term for "unevenness." This term is used to describe a low-contrast, irregular pattern or region that causes uneven screen uniformity under certain conditions. Mura is a result of the deterioration of the liquid crystal (LC) alignment layer; most commonly caused by long-term operation under high ambient temperatures. It is an industry-wide phenomenon and Mura is not repairable.

Mura has been around since the introduction of LCD technology. LCD screens are getting bigger, touch monitors typically run 24/7, and we are enjoying more content now in low light conditions. All these factors add to the possibility of Mura affecting displays.

Symptoms

There are many manifestations of the Mura condition and the causes are quite diverse. For instance, color Mura (white or yellow, strips) is known as an irregular color distribution. Several possible causes of Mura are:

• Impurities or foreign particles in the crystal matrix
• Uneven distribution of LCD matrix during manufacturing
• Non-uniform luminance distribution of the backlight
• Panel assembly induced stress
• Flaws in the LCD cells
• Thermal induced stress - high temperature operation over long periods of time

Recommendations to Avoid Mura

Generally, the appearance of Mura can be minimized by the following methods:

• Lower the backlight brightness
• Use a screen saver
• Reduce the ambient temperature around the unit

Elo Mura specifications

Mura-like image retention is not covered by the Elo TouchSystems product warranty.

The visual performance of liquid crystal displays (LCDs) has usually been evaluated by visual inspection. One of the visual problems hardest to recognize are regions of low contrast and non-uniform brightness or Mura. The accurate and consistent detection of Mura is extremely difficult as it can appear in various shapes and sizes and the inspection results tend to be subjective and based on opinion. As Mura does not lend itself to quantitative measurement, no specification for Mura is available.