What is MURA in LCD Screens and How to Avoid Mura?

Regarding MURA, this is a key professional term in the display industry and optical inspection field.

Core Definition: What Exactly is MURA?

MURA (often transliterated into Chinese as “MURA” or translated as “cloud pattern,” “stain,” or “display non-uniformity”) refers to a defect on a display screen characterized by uneven brightness or color. It manifests as a visually discernible difference in brightness or color between a localized area of the screen and its surroundings; however, it lacks a clear boundary. Typically, it appears as cloud-like, patchy, or streaky patterns.

In short, MURA can be described as a screen appearing “dirty” or exhibiting “uneven color or brightness.” Nevertheless, it should be noted that this is not caused by dust—rather, it is an inherent defect of the panel itself.

Key Characteristics of MURA

Understanding MURA’s traits helps in identification. Its key characteristics include:

1. Non-uniformity: The core issue is uneven brightness or color.
2. No Clear Boundary: Unlike point defects like dead pixels, MURA transitions gradually and blurrily.
3. Viewing Condition Dependent: It is most visible on solid-color images, especially low grayscale levels like gray or white, and often less noticeable in dynamic content.
4. Subjectivity: Determining its severity involves some personal judgment, which is why objective industry standards are necessary.

Common Types of MURA (Based on Shape and Cause)

MURA appears in various forms, each linked to specific manufacturing issues:

Why Does MURA Happen? Root Causes Explained

MURA originates from the unavoidable physical non-uniformities in the display panel manufacturing process. The specific causes vary across different display technologies.

Causes of MURA in LCD Screens

LCD Screens:

• Uneven backlight (LED/diffuser variations)
• Inconsistent glass gap thickness
• TFT transistor differences

OLED Screens:

• Uneven organic material coating
• Moisture/oxygen leakage in pixels
• TFT drive inconsistencies

Assembly Issues:

• Mechanical pressure, dust, or uneven glue during assembly can also cause MURA.

How is MURA Detected and Evaluated?

Since human vision is subjective, the industry relies on objective methods:

1. Machine Vision Inspection: Uses high-resolution CCD cameras to capture specific test patterns displayed on the screen (e.g., full white, full black, grayscale images). Image analysis algorithms then evaluate the brightness/color distribution and calculate the degree of non-uniformity.
2. Key Quantification Metrics:
   1. Signal-to-Noise Ratio (SNR): Measures the contrast of the non-uniform area.
   1. Brightness Difference (ΔL): The brightness difference between the brightest and darkest points.
   1. Standard Deviation (σ): The standard deviation of the brightness distribution across the entire screen.
3. Industry Standards: Major panel manufacturers and brands (e.g., Apple, Samsung, LG) have stringent internal MURA acceptance criteria. Panels exceeding these limits are classified as defective.

How is MURA Different from Other Screen Defects?

Summary: What You Need to Know About MURA

In conclusion, here are the essential takeaways:

• What is MURA: An area defect causing uneven brightness/color without clear borders.
• Why it matters: It is a core metric for display panel quality grades (A-grade, B-grade), directly impacting user experience and product tier.
• Can it be fixed: It cannot be completely fixed by software as it’s a physical defect. However some manufacturers use “De-Mura” compensation technology to mitigate the effect visually, but this is a corrective measure, not a fundamental solution.

Final Tip: Therefore, when purchasing a monitor or phone, if screen purity is critical, you should display full-white and full-gray images upon receipt to check for obvious MURA.