Why do LCD screens produce light spots?
Date:2025-12-29
The generation of light spots (also known as bright spots, bright spots, light leakage or "cloud spots") on LCD screens is a common problem, which is mainly caused by the following two types of reasons. The nature and solutions of these two types of reasons are completely different:
Category 1: Internal reasons of the screen - uneven backlight or malfunction
This is the most common and core reason. The LCD screen itself does not emit light and relies on the backlight module (usually LED light strip) on the back to provide a light source. The generation of light spots is due to the uneven transmission and diffusion of backlight light.
1. Backlight module issue
LED bead malfunction or uneven aging: The backlight module is composed of multiple LED beads. If the brightness of one or several light beads is inconsistent with other light beads (too bright, too dark, or prematurely aged), it will form dot or block like bright/dark spots on the screen.
Defects or damage to the light guide plate: The light emitted by the LED needs to be evenly spread throughout the entire screen through a transparent "light guide plate". If there are scratches, impurities, heat deformation, or dust or oil stains on the surface of the light guide plate during production, the light will scatter unevenly when passing through, forming foggy or cloud like light spots.
Optical film problem: There are multiple layers of optical films such as brightening film and diffusion film on the light guide plate. If these membranes have wrinkles, scratches, or improper assembly, it can also cause uneven distribution of light, resulting in bright or dark spots.
Deformation caused by structural pressure: This is one of the most common reasons. Uneven pressure on the screen during assembly (such as tightening screws or squeezing borders), or accidental pressing or bumping of the screen by the user during use, can cause slight physical deformation of the internal light guide plate or optical film, thereby changing the optical path and producing permanent light spots. The light spot that appears when pressing the edge of the screen with your hand is a typical example.
2. Problems with the LCD panel itself
Highlight/Bad Spot: This is a single pixel fault. If a sub-pixel (red, green, blue) remains in a "constant brightness" state, it will form a very small but dazzling colored or white light spot, which is clearly contrasted with the surrounding area.
Internal contamination of the panel: During the production process, if the packaging of the LCD panel is not strict, small dust or impurities may enter the LCD layer, which may also form fixed spots during display.
Category 2: External factors of the screen - optical interference and reflection
The "light spot" caused by such reasons is usually not a screen malfunction, but an optical phenomenon.
1. Screen surface coating reflection (glare/reflection): Especially in black or dark images, the screen surface will reflect the ambient light around you like a mirror (windows, desk lamps, walls, etc.). If the reflected light source is a point (such as a light bulb), it will form a bright spot; If it is a large area (such as a window), it will form a whitish area. This is not screen damage, but it greatly affects the visual experience.
2. Screen protector/glass bonding issue: If the film or additional glass protective shell applied to the screen is of poor quality, or if there are bubbles or dust during bonding, the uneven surface will cause light refraction and interference, forming rainbow patterns or misty patches.
3. Interference from ambient light sensors (rare): If the automatic brightness adjustment function of some devices malfunctions or the sensor is obstructed, it may cause abnormal brightness in certain areas of the screen.
How to make simple judgments and solutions?
Determine whether it is an internal or external issue:
Shut down or display a pure black image: In a completely dark environment, display a pure black image on the screen. If the light spot still exists at this time, it can be basically determined that it is a backlight problem.
Changing the viewing angle: If the bright spot is caused by external reflection, when you move your head or change the screen angle, the position and shape of the bright spot will change accordingly. The light spot caused by internal backlight issues is relatively fixed.
Gently press: If the shape or size of the light spot changes when gently pressing the screen border or back, it is likely that the internal components are deformed due to pressure (this method should be used with caution and may worsen the problem).
terms of settlement:
For internal backlight/panel faults: During the warranty period, contact the official after-sales service as soon as possible for inspection and repair (usually replacing the entire screen module). After the warranty period, the repair cost may be higher.
For external reflection/interference issues:
Adjust the usage environment to avoid direct sunlight on the screen.
Use screens or films with anti reflective (AG) coating.
Check and reapply the screen protector.
Appropriately increasing the screen brightness can reduce the degree of glare.
Summary
Reason type | Main reason | Feature | Solution |
Internal fault | Backlight module issues (LED, light guide plate, film, pressure) | Fixed position, visible in pure black screen, may vary with pressure | After sales maintenance (replacement of backlight or screen) |
Internal fault | LCD panel bad/bright spots | Extremely small fixed color dots | If the number of bad pixels is small, it is within the allowable range of the industry, and if it is large, it needs to be repaired |
External phenomena | Environmental light reflection/glare | Disappear in pure black images with changes in perspective and ambient light | Improve ambient lighting and use anti glare film |
External phenomena | Poor adhesion of protective film/glass | Usually accompanied by bubbles and rainbow patterns | Re attach or replace high-quality protective film |
Simply put, if the light spot still exists and is fixed in position when displaying black, it is usually a problem with the screen hardware (especially the backlight system) and requires professional repair. If the light spot moves with the light and angle of view, it is mostly caused by environmental reflections.
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