"Our double-sided digital signage looks clear from the front, but when customers walk from the side of the elevator entrance, the screen appears fogged up."
This was the feedback we received from a retail customer last week. The root cause of the problem was a "blind spot" in optical performance testing.
In the digital signage industry, 85% of purchasing decisions focus on size, brightness, and price, neglecting the core parameters that truly impact long-term user experience.
As a provider of commercial display solutions deployed in shopping malls, airports, and medical facilities for many years, we have tested over 200 screens and found that screens with impressive lab specifications may exhibit poor display quality in real-world scenarios due to optical performance issues.
The Importance of Optical Performance in LCDs
Commercial displays are frequently found in various commercial sectors, and their optical performance directly determines the effectiveness of information transmission, affecting whether viewers in different positions can have a consistent visual experience.
Commercial environments typically require support for multi-viewing angles. Good optical performance ensures that viewers from the side can clearly read the content, avoiding information loss due to viewing angle issues. This is especially crucial in high-traffic areas.
The stability of optical parameters affects the long-term performance of the device. Commercial displays often need to operate continuously, and excellent optical performance ensures that the display effect does not significantly degrade over time, guaranteeing a return on investment.
From a user experience perspective, a comfortable and clear display can extend viewer dwell time. In retail and education scenarios, this directly relates to conversion rates and learning outcomes, making it an indispensable technical factor.
5 core indicators of optical performance
Brightness Attenuation Rate
Brightness attenuation rate, more specifically called "viewing angle brightness attenuation rate," is used to quantify the ability of a display screen to maintain brightness at different viewing angles.
It directly determines the user's experience when viewing an LCD screen from the side. It refers to the ratio between the white screen brightness measured at a specific viewing angle and the white screen brightness measured at a perpendicular angle (0° viewing angle) directly in front of the screen.
This metric directly reflects the degree of brightness loss when users view the screen from the side. In commercial scenarios where multiple people view the screen simultaneously, such as digital signage or conference screens, a lower brightness attenuation rate ensures that each viewer can have a clear and bright visual experience, avoiding problems such as the screen turning white or dark.
①Brightness Attenuation Rate Test Procedure:
Place the display screen in a dark room with ambient light below 1 lux, and preheat it for 5 minutes with a white screen until performance stabilizes. Use a CS2000 or CA410 device to measure the center brightness value at a distance of 50cm at a 0° angle in the normal direction.
Then, rotate the platform sequentially to 30°, 45°, and 60° angles, measuring the brightness in the top, bottom, left, and right directions respectively. Substitute these measurements into the formula to calculate the attenuation rate.
② Recommended Criteria For Brightness Attenuation Rate:
According to the current mainstream customer standards for controlling the brightness attenuation rate of LCD display modules, the attenuation rate in all directions at a 30° viewing angle should be ≤70%.
The larger the viewing angle, the more obvious the attenuation usually is. Using brightness enhancement films such as APF or DBEF can significantly improve performance. These technical characteristics should be the focus when purchasing.
Contrast Ratio Attenuation
Contrast ratio attenuation is a key indicator of an LCD display's ability to maintain image detail and clarity at different viewing angles.
It is defined as the ratio of the screen's contrast ratio (the ratio of white to black brightness) at a specific viewing angle to its contrast ratio at a directly perpendicular viewing angle.
A higher contrast ratio attenuation means that the image is more likely to appear "grayish" or "washed out" when viewed from the side, resulting in loss of detail in dark areas and reduced text readability.
① Contrast Ratio Reduction Test Procedure:
In a standard darkroom environment, the LCD module is powered on, switched to an L255 white screen, and run continuously for at least 5 minutes to allow it to reach thermal stability (optical performance stability).
The brightness values of the L255 white and L0 black screens are measured at a 0° angle between the test lens and the normal direction of the LCD module plane, respectively, and the initial contrast ratio is calculated.
Subsequently, the test platform is rotated so that the normal direction of the LCD module plane forms angles of 30°, 45°, and 60° with the test equipment lens, and the brightness values of the L255 white and L0 black screens are measured again, and the contrast ratio is calculated.
② Recommended Criteria for Contrast Ratio Attenuation:
At a 30° viewing angle, a contrast ratio attenuation of ≤70% is also recommended. The key is whether the blacks are "black enough," which is directly related to the panel itself and the selection of the polarizer.
Excessive attenuation will cause the image to appear grayish and text edges to be blurred when viewed from the side.
Color Shift
Color shift, often referred to as "color cast," is used to evaluate the accuracy of color display on a screen under different viewing angles. It characterizes the difference between the color presented at a wide viewing angle and the standard color at a normal viewing angle. The industry commonly uses JNCD (Joint Navier-Standard Diameter) to characterize color shift.
If color shift is significant, the same screen will display inconsistent hues (e.g., appearing yellowish or bluish) at different angles, severely impacting the consistency of a brand's visual image. This metric is particularly important in scenarios where color consistency is crucial, such as retail displays and advertising.
① Color Shift Test Procedure:
Under darkroom conditions, the screen displays a white image and reaches thermal stability. The CIE 1976 color coordinates u'v' are measured at the 0° normal position as a baseline. The test platform is rotated to 30°, 45°, and 60° angles, and the color coordinates of the white image are measured again at each angle.
The u,v coordinate values measured from different viewing angles and orientations are substituted into the color shift calculation formula to calculate the color shift at different viewing angles and orientations.
② Color Deviation Judgment Standards:
The smaller the color deviation of an LCD display module, the smaller the color difference, and the better the color reproduction.
According to current mainstream customer standards for controlling the contrast ratio decay of LCD display modules, color deviation should be controlled at ≤3 JNCD at a 30° viewing angle, and at ≤4 JNCD at a 45° viewing angle.
Color Uniformity
Color uniformity, also often referred to as color uniformity, is a parameter that evaluates the consistency of color reproduction across different areas of a display screen.
Due to factors such as manufacturing processes and backlight distribution, slight color differences may appear in different locations on the same screen.
Color uniformity quantifies this difference by measuring the color coordinates of multiple test points and calculating the maximum deviation between them.
Poor color uniformity manifests as visible color spots or unnatural color transitions, severely impacting the overall visual effect and professional feel of large-size displays.
① Color Uniformity Test Procedure:
Under darkroom conditions, after the screen displays a white image and reaches thermal stability, test points are set according to size (135 points for 5-7 inches, 187 points for 7 inches and above).
Using a surface measurement device CA2500A or a spot measurement device CS2000, the overall effect of the LCD display module is tested. The diameter of the test spot is approximately 1.56mm.
Before testing, ensure the test lens and the normal direction of the LCD display module plane form a 0° angle, and maintain a distance of 50cm between the test lens and the display module. Test the white point color coordinates (u and v) of all points on the entire LCD display module under CIE1976 on an L255 white screen.
Substitute the u and v coordinates of all test points within the LCD AA surface into the color uniformity calculation formula to calculate the color shift between any two points and between any two adjacent points.
② Recommended Control Standards For Color Uniformity:
According to current customer control standards for color uniformity of LCD display modules, the color deviation ∆u'v' between any two points should be ≤3.75 JNCD (≤0.015), and the color deviation between two adjacent points should be ≤1.5 JNCD (≤0.006).
Color Accuracy
Color accuracy specifically refers to the color difference between the ink area of the fully laminated screen cover and the display area, which requires a seamless black effect. The smaller the color difference value, the better the seamless black effect, and the lower the corresponding color accuracy value (Delta E).
Of course, the color difference mentioned here usually refers to color accuracy under a vertical viewing angle, which is different from the color deviation that occurs when the viewing angle changes, as discussed earlier.
Color Accuracy Control Standards:
The color difference ΔE between the cover ink area and the display area of a fully laminated display should be ≤3-4. For high-end applications, ΔE < 2 is recommended to achieve a good seamless black effect.
For flagship products, when ΔE ≤ 1, the display boundary is almost invisible when the screen is off. Note that the L, a, and b values in the ΔE calculation represent the degree of difference in brightness, red-green axis, and yellow-blue axis, respectively.
Choosing the Right Commercial Display for Your Needs
Create a procurement checklist based on these five indicators: conduct on-site testing of brightness and color variation at a 30° viewing angle, request a color uniformity distribution diagram, confirm the specific value of color accuracy ΔE, and prioritize suppliers that provide complete darkroom testing reports.
Selecting a commercial display requires considering the specific application scenario. For retail environments, prioritize color shift and color accuracy to ensure accurate brand color transmission; for control rooms, focus on contrast degradation rate to ensure clear and discernible details.
Before deployment, request the supplier to provide a commitment to the optical performance consistency of screens from the same batch to avoid visual differences caused by mixing different batches and ensure stable performance over a five-year service life.
If your screen involves special installation angles or complex lighting environments, we recommend contacting us for more information on LCD displays and solutions.
