CONTENTS
Foreword
1 Scope
2 Normative References
3 Terms, Definitions, and Abbreviations
3.1 Transparent Automotive Micro LED Display
4 Standard Measurement Conditions
4.1 Standard Test Atmospheric Conditions
4.2 Standard Darkroom Conditions
4.3 Optical Measurement Instruments
4.4 Test Layout
4.5 Conditions for Testing Stability
4.6 Conditions for High-Temperature Testing Stability
5 Optical Requirements
5.1 Luminance
5.2 High-Temperature Color Shift
5.3 Color Gamut Area Ratio
5.4 Luminance Uniformity
5.5 Chromaticity Non-Uniformity
5.6 Primary Wavelength Error
5.7 Color Purity
5.8 White Point Color Coordinates
5.9 Diffuse Reflectance
5.10 Transmittance
5.11 Haze
5.12 Halo
6 Test Methods
6.1 Luminance
6.2 High-Temperature Color Shift
6.3 Color Gamut Area Ratio
6.4 Luminance Uniformity
6.5 Chromaticity Non-Uniformity
6.6 Primary Wavelength Error
6.7 Color Purity
6.8 White Point Color Coordinates
6.9 Diffuse Reflectance
6.10 Transmittance
6.11 Haze
6.12 Halo
Foreword
This document has been drafted by the provisions of GB/T 1.1-2020 “Directives for Standardization – Part 1: Rules for the Structure and Drafting of Standardization Documents.”
Please note that some content in this document may involve patents. The issuing organization of this document does not assume responsibility for identifying such patents. This document is proposed under the jurisdiction of the China Video Industry Association (CVIA).
Drafting organizations of this document include Tianma Institute of New Display Technologies (Xiamen) Co., Ltd., Tianma Microelectronics Co., Ltd., BOE Technology Group Co., Ltd., TCL China Star Optoelectronics Technology Co., Ltd., AU Optronics (Xiamen) Co., Ltd., Chongqing HKC Optoelectronics Technology Co., Ltd., Shanghai Tianma Microelectronics Co., Ltd., Xiamen Tianma Microelectronics Co., Ltd., BOE Crystal Chip Technology Co., Ltd., Altair Display Technology Co., Ltd., Xiamen University, University of Electronic Science and Technology of China, Shenzhen Refond Optoelectronics Co., Ltd., Guangzhou Hongli Display Electronics Co., Ltd., Xi’an NovaStar Tech Co., Ltd., Suzhou Megvii Technology Co., Ltd., Wuhan Jingce Electronic Group Co., Ltd., Hangzhou Yuanfang Optoelectronic Information Co., Ltd., Visco (Shanghai) Optoelectronic Technology Co., Ltd., Suzhou Jingli Optoelectronics Co., Ltd.
The principal drafters of this document are: An Feifei, Peng Xuhui, Qin Feng, Xi Kerui, Hao Yabin, Feng Xiaoxi, Peng Jianfeng, Li Xin, Zhou Wenqi, Wang Xiaoling, Wu Tianyi, Gong Weibin, Huang Weidong, Sun Yuanhao, Dun Shengbao, Zhuang Jianbang, Ding Xinyu, Liang Wenji, Guo Weijie, Zhang Jiaxian, Sang Jian, He Guojing, Feng Yanli, Zheng Zhongming, Yu Yunshan, Zou Qicai, Zhu Jianfei, Tan Guanghui, Liu Luning, Wang Zhou, Ye Kun, Song Li, Shen Huan, Zhang Lili, Zhu Yuliang, Feng Lin, Shi Xiaoyu.
This is the first edition of this document.
Technical Specification for Optical Performance of Transparent Automotive Micro LED Displays
1 Scope
This document specifies the optical performance requirements and testing methods for transparent automotive displays and display modules using Micro Light Emitting Diodes (Micro LEDs) (hereinafter referred to as “displays”). This document applies to the design, production, and acceptance of transparent automotive displays and display modules using Micro LEDs. Other application scenarios may refer to this document as appropriate.
2 Normative References
The following documents are indispensable for the application of this document through normative references in the text. For dated references, only the version corresponding to that date applies to this document; for undated references, the latest version (including all amendments) applies.
- GB/T 2410-2008: Determination of Luminous Transmittance and Haze of Transparent Plastics
- GB/T 3978: Geometrical Conditions for Standard Illuminants
- SJ/T 11141: General Specification for LED Displays
- SJ/T 11281-2017: Test Methods for LED Displays
- T/CVIA 126-2023: Technical Specification for Optical Performance of Micro LED Displays for Automotive Applications
3 Terms, Definitions, and Abbreviations
The terms, definitions, and abbreviations defined in SJ/T 11141, SJ/T 11281-2017, and T/CVIA 126-2023 apply to this document.
3.1 Transparent Automotive Micro LED Display
Transparent automotive Micro LED display
A transparent automotive Micro LED display refers to a transparent panel that uses Micro LED chips (Micro LED Chip) with a length of less than 100 micrometers and a width of less than 50 micrometers, without a substrate, to display information.
4 Standard Measurement Conditions
4.1 Standard Test Atmospheric Conditions
Unless otherwise specified, all tests are conducted under the following temperature, humidity, and atmospheric pressure conditions:
a) Temperature: 25°C ± 3°C;
b) Relative humidity: 25%–75%;
c) Atmospheric pressure: 86 kPa–106 kPa.
4.2 Standard Darkroom Conditions
Unless otherwise specified, the illumination of the testing environment should be less than 1 lx.
4.3 Optical Measurement Instruments
- Luminance Colorimeter: Luminance error ≤ ±3%, chromaticity error ≤ ±0.003. Similar instruments for measuring optical performance such as luminance and chromaticity may also be used.
- Colorimeter: Equipment meeting the requirements of GB/T 3978 for diffuse 8° geometry, including specular reflection light (denoted as di:8°).
- Haze Meter: Haze testing instrument that meets the geometric requirements specified in GB/T 2410-2008.
- Transmittance Meter: Transmittance testing instrument that meets the geometric requirements specified in GB/T 2410-2008.
- Imaging Luminance Meter: Luminance error ≤ ±3%, chromaticity error ≤ ±0.003, field of view ≥ 50×50 mm, resolution capability ≤ 1 mm.
Note: To maintain the accuracy and repeatability of optical measurement instruments, calibration should be performed periodically according to the instrument manufacturer’s recommended schedule.
4.4 Test Layout
The standard test setup for the luminance colorimeter is shown in Figure 1:
a) Unless otherwise specified, the luminance colorimeter should be perpendicular to the measurement surface of the display during testing;
b) An appropriate testing distance and measurement field angle should be used depending on the equipment, and the measured area should include at least 500 pixels in a circular or rectangular region.
Description of Index Numbers:
1 — Display screen;
2 — Luminance colorimeter;
S — Measurement area;
θ — Measurement field angle;
L — Measurement distance.
4.5 Conditions for Testing Stability
As shown in Figure 1, the luminance colorimeter standard test setup requires the display screen to be set at its rated luminance with a full white field. A preheating period of at least 30 minutes is necessary until the luminance of the display screen stabilizes (i.e., the variation per minute is less than 2% of the average value, where the average is determined from at least 10 measurements over 10 minutes). Once stability is achieved, measurements can begin.
4.6 Conditions for High-Temperature Testing Stability
The high-temperature test setup is illustrated in Figure 2. The display screen should be placed inside a thermal chamber adjusted to the designated temperature, T. The conditions for achieving high-temperature testing stability are met when the ambient temperature inside the chamber is maintained at T ± 2°C for at least 10 minutes, and the luminance of the display screen reaches a stable state (i.e., the variation is less than 2% of the average value, where the average is determined from at least 10 measurements over 10 minutes).
Description of Index Numbers:
1 — Luminance colorimeter;
2 — Thermal chamber cover;
3 — Test opening;
4 — Clamping mechanism;
5 — Display screen;
6 — Thermal chamber.
5 Optical Requirements
The optical requirements outlined in this document refer to the general standards for automotive transparent products. If the customer has specific requirements, those should take precedence.
5.1 Luminance
The luminance of the display screen under a full white field at room temperature should meet the requirements specified in Table 1 for 13 different measurement angles.
| Viewing Angle | Measurement Angle | Requirement | |
| Horizontal Angle θH | Vertical Angle θV | ||
| Frontal View | 0° | 0° | ≥1000 |
| A+ Angles | +10° | +8° | Lower limit ≥ positive viewing Angle brightness value *90%; Upper limit ≤ positive viewing Angle brightness value *105% |
| +10° | -4° | ||
| -10° | +8° | ||
| -10° | -4° | ||
| A Angles | +40° | +20° | Lower limit ≥ positive viewing Angle brightness value *80%; Upper limit ≤ positive viewing Angle brightness value *105% |
| +40° | -10° | ||
| -40° | +20° | ||
| -40° | -10° | ||
| B Angles | +50° | +20° | Lower limit ≥ positive viewing Angle brightness value *75%; Upper limit ≤ positive viewing Angle brightness value *105% |
| +50° | -10° | ||
| -50° | +20° | ||
| -50° | -10° | ||
The luminance of the display screen under a full white field at 70°C and 85°C should meet the requirements specified in Table 2 for 13 different measurement angles.
| Temperature | Requirement |
| 70±2℃ | ≥ 70% of the Luminance at Room Temperature |
| 85±2℃ | ≥ 50% of the Luminance at Room Temperature |
5.2 High-Temperature Color Shift
The color coordinates of the display screen under a full white field at a high temperature of 85°C should deviate no more than |△x| ≤ 0.03 and |△y| ≤ 0.03 from those at room temperature.
5.3 Color Gamut Area Ratio
The color gamut area of the display screen should be at least 110% of the NTSC color gamut area (GNTSC ≥ 110%).
5.4 Luminance Uniformity
The luminance uniformity (Lu) of the display screen should not be less than 75%.
5.5 Chromaticity Non-Uniformity
The chromaticity non-uniformity of the display screen should not exceed 0.01.
5.6 Primary Wavelength Error
The error between the peak wavelength of each primary color (R/G/B) of the display screen and its nominal wavelength should not exceed ∆λ ≤ 7 nm.
5.7 Color Purity
The color purity of the display screen should comply with the requirements specified in Table 3.
| Primary Color | Color Purity |
| Red | ＞97% |
| Green | ＞85% |
| Blue | ＞97% |
5.8 White Point Color Coordinates
The difference between the white point color coordinates of the display screen and the standard D65 white point (6500K, x=0.3127, y=0.329) should satisfy |△x| ≤ 0.03 and |△y| ≤ 0.03.
5.9 Diffuse Reflectance
The di:8° diffuse reflectance (SCI) of the display screen, including specular reflection light, should not exceed 5%.
5.10 Transmittance
The transmittance of the display screen should be greater than 50%; if used for the front windshield, it should be greater than 70%.
5.11 Haze
The haze value (H) of the display screen should not exceed 10%.
5.12 Halo
The halo of the display screen should meet the requirements specified in Table 4.
6 Test Methods
6.1 Luminance
Refer to Section 6.1 of T/CVIA 126-2023 for the luminance testing method.
6.2 High-Temperature Color Shift
Refer to Section 6.2 of T/CVIA 126-2023 for the high-temperature color shift testing method.
6.3 Color Gamut Area Ratio
Refer to Section 6.3 of T/CVIA 126-2023 for the color gamut area ratio testing method.
6.4 Luminance Uniformity
Refer to Section 6.4 of T/CVIA 126-2023 for the luminance uniformity testing method.
6.5 Chromaticity Non-Uniformity
Refer to Section 6.5 of T/CVIA 126-2023 for the chromaticity non-uniformity testing method.
6.6 Primary Wavelength Error
Refer to Section 6.6 of T/CVIA 126-2023 for the primary wavelength error testing method.
6.7 Color Purity
Refer to Section 6.7 of T/CVIA 126-2023 for the color purity testing method.
6.8 White Point Color Coordinates
Refer to Section 6.8 of T/CVIA 126-2023 for the white point color coordinate testing method.
6.9 Diffuse Reflectance
Measure the display screen’s di:8° diffuse reflectance under CIE D65 illumination conditions. The testing steps are as follows:
a) Ensure the testing environment meets the requirements of Section 4.2;
b) Refer to the schematic in Figure 3 and use a colorimeter set to CIE D65 diffuse illumination conditions. After performing black and white calibration, place the sampling port in contact with the display surface, ensuring no other objects are placed within 50 mm behind the test area;
c) The test area should include no fewer than 500 adjacent pixels;
d) Set the display screen to an unlit state;
e) Record the di:8° diffuse reflectance SCI value of the display screen.
Description of Index Numbers:
1 — Colorimeter receiver;
2 — Light source;
3 — Screen shield;
4 — Display screen;
5 — Integrating sphere.
6.10 Transmittance
To measure the percentage of luminous flux transmitted through the screen relative to the luminous flux incident on the sample, the following steps should be performed:
a) Use a transmittance tester, and set the light source type to CIE D65 or CIE C mode; the type of light source used must be specified;
b) Ensure the test area covers no fewer than 500 adjacent pixels;
c) Set the display screen to an unlit state;
d) Refer to GB/T 2410-2008 to complete the screen transmittance (Tr) test;
e) Calculate the transmittance (Tr) using incident light flux (T1) and total transmitted light flux through the sample (T2) according to formula (1).
6.11 Haze
The haze is measured as the percentage of scattered luminous flux deviating from the direction of the incident light relative to the transmitted luminous flux (considering scattered luminous flux deviating more than 2.5° from the direction of incident light for haze calculation). The testing steps are as follows:
a) Use a haze meter with the light source type recommended to be set to CIE D65 or CIE C mode; the type of light source used must be specified;
b) Ensure the test area covers no fewer than 500 adjacent pixels;
c) Set the display screen to an unlit state;
d) Use the haze meter to measure the haze value (H) of the screen, referring to Section 7.1 of GB/T 2410-2008.
6.12 Halo
The test equipment should use an imaging luminance meter, and the test setup is shown in Figure 4. Given the transparency characteristics of the display screen, the screen should be elevated with spacers around its perimeter to a height of at least 5 mm before testing to prevent direct contact between the display screen and the test platform.
Description of Index Numbers:
1 — Imaging luminance meter;
2 — Display screen;
3 — Spacer;
4 — Test platform.
Main Test Steps:
a) Place the display screen and the imaging luminance meter under standard testing conditions;
b) Set up the testing system;
c) Adjust the display screen to show the test pattern with a black border and a white central frame, as shown in Figure 5 (actual observed effect shown in Figure 6);
d) The size of the white frame should be 20×20 mm (if the display screen size is smaller, the white frame size can be reduced to 10×10 mm or 5×5 mm), and maintain this setting for 5 minutes.
e) Adjustment of the Imaging Luminance Meter: Set the field of view to be at least three times the size of the white frame, i.e., ≥60×60 mm. The image single-point resolution should be at least equal to the pixel pitch of the display screen and no greater than 1 mm. Measure the luminance value of the bright area (Lw) by directly measuring the overall luminance. Lw is defined as the average luminance within a square region that is 2 mm inward from each edge of the test input pattern (16×16 mm), corresponding to the red frame area shown in Figure 7.
f) Measurement of Halo Luminance Value (Lhalo): To minimize the impact of glare from the imaging system, use a MASK made of black opaque material to cover the bright area before measuring the halo luminance. The MASK should have the same size as the white frame of the input pattern. After completing the halo luminance measurement, extract the halo luminance values from four different directions at various distances, recorded as Lhalo(x1 = d), Lhalo(x2 = d), Lhalo(y1 = d), and Lhalo(y2 = d). Here, “d” represents the distance from the data collection point to the white frame, with the starting point set at the midpoint of each direction of the test pattern. Distances of 1 mm and 5 mm should be used (refer to Figure 8 for the illustration of x1 and y1 directions).
g) Calculate the halo values (Halo) for the four directions at different positions (with “d” set at 1 mm and 5 mm, respectively) using formula (2).
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Original article comes from the China Video Industry Association.
Edited and translated by MiniMicroLED Insights (Doris).