How to reduce light leakage on LCD screens?

• By IDT

How to reduce light leakage on LCD screens?

The control of LCD screen light leakage is a dual project of "source process+assembly specification ": panel manufacturers reduce light leakage from the source through backlight optimization and full lamination technology;

Light leakage in LCD screens refers to the phenomenon where the light from the backlight module overflows from the edges of the screen, border gaps, or panel junctions, resulting in uneven bright spots at the edges of the screen. It is almost impossible to completely eliminate light leakage (limited by the manufacturing process of LCD panels), but the degree of light leakage can be significantly reduced through design optimization, process control, and installation specifications. The following are specific solutions for different scenarios:

I. Panel manufacturing stage: source control of light leakage (core process of panel factory)

The root cause of light leakage is the scattering of backlight module light and the bonding gap between the panel and backlight. Panel manufacturers need to optimize the structure and process:

1. Backlight module optimization

Precision design of light guide plate (LGP): laser engraved dots are used instead of traditional printing dots to evenly diffuse light and reduce edge light concentration; The edges of the light guide plate should be frosted or chamfered to avoid direct light from shining on the frame.

Stacking optimization of Brightening Film (BEF) and Diffusion Film: Adjust the film angle and number of layers, control the direction of light propagation, and prevent edge light from overflowing; Add black tape to the edge of the backlight module to block side light leakage.

Frame shading design: High shading black glue or foam is pasted on the inner side of the metal or rubber frame of the backlight module to absorb overflow light and avoid reflection to the panel.

2. LCD panel bonding process

Full lamination technology: using optical adhesive (OCA) instead of traditional air layers to tightly bond the LCD panel with the backlight module, eliminating light scattering caused by gaps. This is the core solution for reducing light leakage in consumer electronic screens (phones, tablets).

Accurate positioning and pressing: using high-precision bonding equipment to ensure alignment between the panel and backlight module, avoiding gaps at the edges; Control the compression pressure evenly to prevent excessive local gaps.

3. Raw material selection

Choose polarizing film and black matrix (BM) with high light blocking rate. The black matrix should cover the non display area at the edge of the panel to block backlight penetration.

The frame material is made of high light blocking ABS or PC material to avoid light transmission.

II. Module assembly stage: installation specification reduces light leakage (equipment manufacturer/assembly plant)

For the assembly of LCD screen modules (LCM), improper operation can exacerbate light leakage, and the following specifications should be followed:

1. Adaptation design of border and shell

The outer shell frame needs to be accurately matched with the edge of the LCD screen module, with a reasonable assembly gap reserved (usually 0.1-0.3mm). If the gap is too large, it can easily cause light leakage, and if it is too small, it can squeeze the panel and cause water ripples.

Fill the gap between the frame and the LCD screen with light blocking foam or conductive foam, which not only fills the gap but also absorbs the overflow light and serves as a buffer.

2. Fixed method optimization

Adopting a uniform force snap fastener instead of screw hard pressing to avoid uneven screw pressure causing local deformation of the panel and the formation of light leakage gaps.

If it is necessary to fix with screws, a buffer pad should be added between the screws and the panel to control the tightening force.

3. Avoid panel deformation

Handle with care during assembly to prevent panel bending and compression; It is strictly prohibited to press the edge of the panel with hands (which may cause delamination between the polarizer and the glass, resulting in light leakage).

When storing modules, keep them level and avoid stacking and heavy pressure.

III. Terminal use stage: Reduce the impact of light leakage (user end)

For purchased LCD screen devices, users cannot eliminate light leakage from hardware, but can reduce visual impact through the following methods:

1. Adjust display parameters

Reduce screen backlight brightness: The visual effect of light leakage is less obvious at low brightness, and the brightness can be adjusted according to the usage environment (such as adjusting the indoor environment brightness to below 50%).

Enable local dimming (HDR) function (only supported on OLED or high-end LCD screens): Control the brightness of backlight zones through algorithms to reduce visual contrast of edge bright spots.

2. Optimize the usage environment

Avoid using in a completely black environment: A completely black environment will amplify the visual difference of light leakage, and can be paired with night lights or ambient light to balance the brightness contrast between the screen and the environment.

Adjust viewing angle: Some of the light leakage is not obvious when viewed from the front, but more prominent when viewed from the side. Try to maintain a front level view of the screen.

3. Distinguish between normal light leakage and quality issues

Industry standard: Light leakage of LCD panels is a normal process phenomenon, and slight edge bright spots (not affecting normal display) are qualified products; If there is severe light leakage (large bright spot area, high brightness, affecting the viewing of the picture), you can contact the manufacturer for return or exchange.

IV. Key points of light leakage control for different types of LCD screens

Summary

        The control of LCD screen light leakage is a dual project of "source process+assembly specification": panel manufacturers reduce light leakage from the source through backlight optimization and full lamination technology; The equipment factory avoids the aggravation of light leakage through precise assembly and shading design; Users can reduce visual impact by adjusting parameters and optimizing the environment. A completely leak free LCD screen does not exist, but through reasonable process control, light leakage can be controlled within a range that is almost imperceptible to the human eye.

Can I help you organize a checklist for preventing light leakage during the assembly of LCD screen modules, so that you can check each item during production or acceptance? Do you need it?

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