Brightness uniformity in a full-viewing-angle LCM (Liquid Crystal Display) is a core indicator of its display quality, especially when viewed from multiple angles, ensuring no significant decrease in brightness or differences in contrast. Achieving this requires a comprehensive approach encompassing optical design, material selection, structural optimization, and drive control to overcome the brightness uniformity issues that traditional LCMs often exhibit as viewing angles expand.
The combination and optimization of optical films are fundamental to improving brightness uniformity. Full-viewing-angle LCMs typically employ multiple layers of optical films, including diffuser films, brightness enhancement films (such as prism films), and reflective films. Diffuser films eliminate graininess by scattering light, while brightness enhancement films use refraction to refocus large-angle light back to the normal viewing angle, improving axial brightness. For example, the microstructure of prism films can concentrate scattered light in a specific direction, reducing light loss at the edges. Reflective films improve overall light efficiency by recovering unused light from the backlight. The light transmittance, surface roughness, and interlayer bonding precision of these films must be strictly controlled; any minute defects (such as bubbles or scratches) can lead to localized brightness anomalies.
The uniformity design of the backlight directly affects the brightness performance at a full viewing angle of 1 cm. Direct-lit backlighting achieves localized dimming through densely packed LEDs, but the problem of dark areas in the gaps between LEDs needs to be addressed. Optimization methods include adjusting the position and diameter of the light-emitting apertures in the diffuser film and increasing secondary reflection paths to ensure sufficient light diffusion in the LED gap areas. Edge-lit backlighting relies on a light guide plate to convert line light sources into surface light sources. The dot design (size, density, and shape) of the light guide plate needs to be precisely controlled through optical simulation to ensure uniform light emission. Furthermore, the brightness of the backlight must match the transmittance of the LCD panel to avoid light leakage or light decay caused by glass substrate stress or uneven liquid crystal molecule arrangement.
Stress control of the LCD panel is key to reducing black-state light leakage and improving uniformity. During processing or assembly, the glass substrate may experience birefringence due to mechanical stress, causing a change in the polarization direction of light and resulting in light leakage. Reducing the glass thickness can reduce stress sensitivity; for example, reducing the glass thickness from 1.0 mm to 0.5 mm can improve black-state uniformity by approximately 13%. Meanwhile, optimizing the flatness of the iron frame and backlight module to avoid pressure on the panel due to component deformation is also an effective way to reduce stress interference. Furthermore, increasing the size of the lower polarizer can disperse stress, reduce the force per unit area, and further improve black-state uniformity.
The dimming technology of the driver IC is crucial to the dynamic brightness uniformity at a full viewing angle of 1 cm. Local dimming technology controls backlight brightness in zones to match the image content, improving contrast and reducing halo effects. However, too many zones may lead to brightness differences between areas, requiring algorithm optimization to achieve a smooth transition. Global dimming must ensure that all backlight zones respond synchronously to avoid brightness fluctuations caused by drive delay. In addition, gamma correction technology can adjust the non-linear relationship between brightness and drive voltage, ensuring brightness uniformity at different gray levels and avoiding brightness decay at low gray levels.
Material selection and process precision are the underlying support for ensuring brightness uniformity. The light guide plate needs to use high-transmittance acrylic material with a surface smoothness reaching the nanometer level to reduce total internal reflection loss. The bonding of optical films must be completed in a cleanroom to avoid light scattering caused by dust particles. Wavelength consistency of LED beads (e.g., color coordinate deviation Δx/Δy < 0.003) can reduce the impact of color shift on brightness perception. Furthermore, component tolerances must be controlled during assembly to avoid stress concentration caused by deformation of the iron frame or plastic frame, which could lead to uneven brightness.
Environmental adaptability and reliability testing are essential steps before mass production of full viewing angle LCMs. High temperature and humidity environments may accelerate material aging, leading to yellowing of the light guide plate or film detachment; stability must be verified through reliability testing at 85℃/85%RH. Mechanical vibration testing simulates impacts during transportation to ensure that components are not loose or deformed. In addition, long-term illumination testing can detect the light decay curve of the backlight module, ensuring that the rate of brightness uniformity decay over time is within a controllable range.
Improving the brightness uniformity of full viewing angle LCMs requires a continuous process throughout design, manufacturing, and testing. Through optical film optimization, backlight uniformity design, stress control, drive dimming technology, material and process improvements, and environmental adaptability verification, it is possible to achieve no significant difference in brightness when viewed from multiple angles, meeting the stringent requirements of high-end display devices for consistent image quality.
