Nowadays LCDs and LEDs have become an integral part of modern electronics, from smartphones to televisions and industrial equipment. Even a small wearable boasts an AMOLED configuration. Ensuring quality and reliability of the display is crucial, and rigorous electronic devices display validation is essential to meet industry standards and market expectations. In this article, we explore electronic devices display validation, the display testing procedures involved, LCD testing challenges, and effective solutions to overcome them.
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), VA (Vertical Alignment) displays, OLED, AMOLED, POLED, QLED (Quantum dot LEDs), MicroLEDs and the list goes on. As technology and manufacturing processes progress, the display evolves as well.
With respect to interfacing, multiple options exist — HDMI, LVDS, MIPI-DSI, DVI, SDI, DP and more. The choice depends on bandwidth, distance, quality, and requirements. But in general, the underlying concept of electronic devices display validation remains consistent: 2D image data from a framebuffer is transferred over interfaces and rendered pixel by pixel at a rate unrecognizable by the human eye.
Display Testing Procedures for Electronic Devices
While it is ensured that the display panel meets design specifications in terms of size, resolution, and overall appearance, post-assembly electronic devices display validation is essential. Display testing begins with a visual inspection of the LCD panel for defects such as dead pixels, scratches, or irregularities in color uniformity. Based on application and industry, one or more of the following display testing procedures are performed.
| Test | Purpose | Procedure |
|---|---|---|
| Dead Pixel Test | Identify and locate a dead pixel on the screen | For testing, use a solid color background (Red/Green/Blue) and inspect the screen |
| Stuck Pixel Test | Identify whether any pixel is stuck on a single color | Display a solid color and identify pixels that remain constant irrespective of display content |
| Color Uniformity Test | 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 | Identify uneven backlight distribution | Display a black image in a dark room and check for areas where light bleeds through the edges |
| Viewing Angle Test | 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 | Verify that the display accurately reproduces different resolutions | Display images or patterns at various resolutions and check for distortion or artifacts |
| Gamma Correction Test | 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 | Measure the difference between the darkest and brightest parts of an image | Use test patterns to evaluate the display's contrast ratio against specified standards |
| Response Time Test | Assess how quickly pixels can change colors | Display fast transitions between black and white to check for ghosting or trailing effects |
| LED Aging Test | Detect product material quality and production standards | Temperature-adaptive testing, analog voltage range testing, impact destructive testing, and online monitoring of driving power supply and product current/voltage changes |
Standards and Certifications for LCD testing
Consumer Electronics Display Compliance
Several certifications and standards apply to consumer electronics display and LCD/LED products used in electronic devices display validation. Compliance ensures that products meet criteria related to safety, performance, and environmental considerations.
| 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) | 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) | Defines ergonomic and performance requirements for displays, including classification based on pixel defects |
| TCO Certified | A sustainability certification covering 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 Electronic Devices Display Validation
Digital Vision Chart and Engineering Test Mode
As an end product, it is essential to enter a specific mode to validate the displays. Technically called Engineering Test Mode, this allows many peripherals to be tested through a special sequence of operations. In the display testing scenario, predefined color images can be loaded on screen and validated. With image streams, blurriness tests can be performed at different FPS. A digital vision chart is also used to assess sharpness and resolution in a standardized and repeatable way — an important technique in electronic devices display validation.
If the device has online capabilities, sites like displaycal.net or deadpixeltest.org can be used for display testing for blurriness and dead pixels. During product validation, displays must be tested over different temperatures to ensure no artifacts appear within the specified operating range.
Challenges in LCD testing and Electronic Display Validation
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 in LCD testing. 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 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 in electronic devices display validation.
Solutions for Display Testing and Validation
Addressing the challenges in display testing requires innovative solutions. Incorporating dynamic testing scenarios and developing adaptive testing algorithms are essential steps. Leveraging modern camera technologies, it is possible to identify even a single dead pixel in electronic devices display validation. Gamma correction can also be performed automatically at end-of-line production. Advances in AI and machine learning 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 such product that automates all these tests and finds wide application in electronic devices display validation for automotive instrument clusters, industrial HMIs, smart watches, and other consumer electronics display products.
Conclusion
With the advancement in display technologies, electronic devices display validation techniques are expected to evolve to match the quality requirements needed for each product. Rigorous display testing and LCD testing, combined with modern automation tools, ensure that consumer electronics display products meet the highest standards. Keep a tab on our articles to learn about evolving technologies and associated validation procedures. Embien's product engineering services encompass end-to-end electronic devices display validation — from panel bring-up and display testing to full system-level validation — helping teams ship quality products faster.