Nowadays LCD’s and LED’s have become an integral part of modern electronics, from smartphones to televisions and industrial equipment. Even if it is a small wearable, the device boasts of a AMOLED configuration. Ensuring the quality and reliability of the display is crucial, and rigorous testing procedures are essential to meet industry standards and market expectations. In this article, we will explore electronic devices display validation, the challenges involved, and effective solutions to overcome these challenges.
Display Technologies
There are multiple display technologies available in the market today, each catering to a different need and price point. LCDs (liquid crystal displays), TN (Twisted nematic) LCDs, IPS (in-plane switching technology), VA (Vertical alignment) displays, OLED (Organic Light Emitting Diode), AMOLED (active matrix OLDE), POLED (passive matrix OLED), QLED (Quantum dot LEDs), MicroLEDs and the list goes on. As technology and manufacturing processes progress, the display evolves as well.
With respect to the interfacing part, there are multiple options available such as HDMI, LVDS, MIPI-DSI, DVI, SDI, DP and many more. Based on the bandwidth, distance, quality, requirements, one of the interfaces is being used.
But in general, the underlying concept of displays remains the same where the 2D image data from framebuffer is transferred over interfaces and shown in the screen pixel by pixel at a rate unrecognizable by human eye.
Display Test Procedures
While it is ensured that the display panel meets design specifications in terms of size, resolution, and overall appearance, post assembly it is necessary to validate the display.
It is essential to begin with a visual inspection of the LCD panel for any visible defects such as dead pixels, scratches, or irregularities in color uniformity. Then based on the applications and industry, one or more of the below tests are performed on the target display.
Test | Purpose | Procedure |
---|---|---|
Dead Pixel Test | This is to identify and locate a dead pixel on the screen | For testing use a solid color background (Red/Green/Blue) and inspect the screens |
Stuck Pixel Test | This is to identify whether any pixel stuck on a single color | Display a solid color and focus on a pixel remain constant irrespective of display content |
Color Uniformity Test | To check if colors are consistent across the entire screen | Display a uniform color across the screen and inspect for variations or discolorations |
Backlight Bleeding Test | To identify uneven backlight distribution | Display a black image on the screen in a dark room and check for any areas where light appears to bleed through the edges |
Viewing Angle Test | To evaluate how well the display maintains color and contrast at different viewing angles | Observe the screen from various angles to check for changes in color, brightness, or contrast |
Resolution Test | To verify that the display can accurately reproduce different resolutions | Display images or patterns at various resolutions and check for distortion or artifacts |
Gamma Correction Test | To check if the display reproduces shades of gray correctly | Display a gradient of gray colors and check for smooth transitions without banding |
Contrast Ratio Test | To measure the difference between the darkest and brightest parts of an image | Use test patterns to evaluate the display's contrast ratio and ensure it meets specified standards |
Response Time Test | To assess how quickly pixels can change colors | Display fast transitions between black and white to check for ghosting or trailing effects |
LED Aging test | This test is to detect product material quality and production standard | These are temperature adaptive testing, analog voltage range (high, medium, low) testing and impact destructive testing, as well as on-line monitoring of driving power supply and product current, voltage change |
Standards and Certifications for Displays
There are several certifications and standards that apply to Display - LCD (Liquid Crystal Display) and LED (Light Emitting Diode) products. Compliance with these certifications and standards ensures that the products meet specific criteria related to safety, performance, and environmental considerations. Here are some relevant certifications and standards for LCD and LED products.
Standards/Certification | Purpose |
---|---|
ENERGY STAR Certification | Indicates energy efficiency and environmental performance. Products with the ENERGY STAR label meet strict energy consumption and performance criteria |
ISO 9241 (Ergonomics of Human-System Interaction) Standards | Provides guidelines for the ergonomic design of visual display terminals, including aspects related to visual comfort, legibility, and usability |
ISO 13406-2 (Ergonomic Requirements for Work with Visual Displays) Standards | Defines ergonomic and performance requirements for displays, including classification based on pixel defects |
TCO Certified | TCO Certified is a sustainability certification that covers environmental and social responsibility criteria for IT products, including displays |
DisplayHDR Certification | Ensures that high dynamic range (HDR) displays meet specific performance criteria for brightness, contrast, and color reproduction |
Techniques for Display Validation
As an end product, it is essential to enter into a specific mode to validate the displays. Technically called the Engineering Test Mode, where with a special sequence of operations can be initiated that will move the system to a special state where many peripherals can be tested. In the display testing scenario, many predefined color images can be loaded on screen and validated. With some image stream, blurriness tests can be done at different FPS.
In case, the device has online capabilities with browser, sites like https://displaycal.net/ or https://deadpixeltest.org/ can be used for display testing for blurriness and dead pixels on the screen.
During product validation, the displays need to be tested over different temperatures and ensure there are no artifacts observed in the specified operating range.
Challenges in Electronic display testing
Modern displays are dynamic, constantly adapting to changing content and user interactions. Testing dynamic parameters, such as motion handling and response time, poses significant challenges. Traditional static tests may not accurately represent real-world scenarios, leaving a gap between laboratory performance and real-world user experience.
Displays' performance can be influenced by environmental factors, such as temperature and humidity. Achieving consistency in LCD testing across different environments remains a challenge, as the variations can affect results and impact the overall reliability of the testing process. Striking a balance between controlled laboratory conditions and real-world usage scenarios is a constant struggle.
Solutions for Display Validation
Addressing the challenges in display testing requires innovative solutions. Incorporating dynamic testing scenarios and developing adaptive testing algorithms are essential steps. Leveraging the modern camera technologies, it is possible to identify even a single dead pixel. Even the gamma correction can be done automatically at the end of line production. Additionally, advancements in artificial intelligence (AI) and machine learning (ML) can play a pivotal role in creating intelligent LCD testing systems that learn from real-world usage patterns and adapt testing parameters accordingly. TestBot is one kind of product which can do all these tests automatically and finds wide application in electronics devices display validation for products such as automotive instrument clusters, industrial HMIs, smart watches etc.
Conclusion
With the advancement in display technologies, the validation techniques are also expected to evolve to match the quality requirements needed for the product. Keep a tab on our articles to learn about the evolving technologies and associated validation procedures.