LED illuminated signs are the mainstream choice for modern commercial signs. Compared with traditional neon signs or inkjet signs, they have significant advantages in performance and economic benefits, such as excellent visual effect, low-voltage DC power, safety and energy saving, and flexible customization according to needs.
However, LED illuminated signs often have shadow issues, which greatly affects their presentation.
Why is this happening?
In fact, the problem of shadows in LED illuminated signs is mainly affected by several factors, including the performance of the LED light source, the LED module layout, the internal signage structure processing, the panel material, and the power supply. If we can check each of these factors one by one, we can find the answer to the problem.
Below, I will analyze the reasons for the shadow problem in LED illuminated signs and provide a shadow problem troubleshooting checklist to help users address similar issues effectively.
Part 1：7 Causes of Shadows
LED Light Source
The first possibility is the performance difference of the LED chips. Different batches of LED chips (with different bins) have differences in brightness and color temperature, and mixing them will produce dark spots that are visible to the naked eyes.
The second possibility is LED light decay. After a period of use, some inferior LEDs may experience a rapid decrease in brightness in some of the LED beads, which can cause “spotted” shadows to appear on LED illuminated signs.
The third possibility is the angle of the light source. For example, if a wide-angle LED module (120°～160°) is not selected, the light will not reach the entire panel, resulting in a bright center and dark edges.
LED Module Layout
Improper layout of LED lights inside illuminated signs is also a very common technical reason. If the spacing between LED modules or LED strips installed inside the illuminated signs is too large or too dense(light canceling each other) or the distribution is uneven, light shadows will appear.
Improper Light-to-Panel Distance
Some letter casings are deep, such as over 100mm, but the LED lights are only attached to the back panel. This causes light attenuation when the light reaches the panel, resulting in a situation where the center is bright and the edges are dark. Therefore, a reasonable distance is very important. If it is too close, “light spots” will appear, and if it is too far away, light attenuation will result in “shadows”.
No Reflective Coating
Because LED illuminated signs are generally deep, reflective treatment is usually applied to ensure that light reaches the panel effectively, thereby improving light utilization and uniformity. Therefore, if the inner wall of the letter casing is not coated with white high-reflectivity paint, the light utilization rate inside is low, the number of reflections is reduced, which can lead to darker edges and shadows.
Internal Light Obstruction
Internal light obstruction come from two sources: improper handling during factory manufacturing and improper operation during on-site installation.
During factory manufacturing, improper arrangement of internal reinforcing ribs, support columns, or wiring can directly block the light path, creating shadows.
During on-site installation, some cables extending from the inside may not be straightened (parallel to the light source) and may be coiled inside the sign casing, also obstructing the light path and causing shadows.
Panel Material
Panel material issues are primarily related to material quality, color difference in the panel, and the depth of light transmission.
Regarding material quality, for example, uneven light transmittance in acrylic panel or significant thickness variations can lead to uneven light transmission and shadows.
Regarding color difference, certain colored panels absorb specific wavelengths of LED light. If the LED spectrum does not match the panel’s spectrum, it will appear dim or patchy.
Regarding the depth of light transmission, ordinary transparent panel cannot eliminate shadows; professional light guide panel (light diffuser) must be used. These panel contains microcrystalline particles that transform point light sources into surface light sources.
Power Supply
Power supply is also a crucial detail.
If the selected power adapter is underpowered, it won’t be able to support all the LEDs at full power, causing some LEDs to become less bright and creating shadows.
Another issue is when too many LED modules are connected in series. Due to the resistance of the wires, the voltage at the ends will be lower than at the beginning (voltage drop phenomenon). This will cause the front of the illuminated sign to be brighter than the end.
Part 2: Shadow Issue Troubleshooting Checklist
Generally, “well distributed LEDs + white high-reflectivity inner liner + high-quality diffuser” is the most effective solution for solving shadow problems.
However, since the actual situation may be more complex, I have created the following checklist for troubleshooting shadow problems. If shadow problems occur, you can use the following checklist to troubleshoot.
Checklist
| Investigation Dimensions | Core Inspection Items | Judgment Criteria | Abnormal Behavior | Conclusion Record |
|---|---|---|---|---|
| I. Light Source Performance | 1. LED Consistency | Confirm that LED chips from different bins are not mixed. | Localized yellowing, bluish tint, or inconsistent brightness | □ Pass □ LED Issue |
| 2. Optical Degradation | Check if any LED chips are blackened or dimmed. | “Spotted” shadow appears. | □ Pass □ LED Issue | |
| 3. Beam Angle | Confirm whether a wide-angle (120°–160°) LED module is used. | Bright center with dark edges. | □ Pass □ Wrong LED Module Selection | |
| II. LED Module Layout | 4. LED Module Spacing | Check if module spacing is too large or too dense or uneven. | Visible Striping. | □ Pass □ Layout Issue |
| 5. Light-to-Panel Distance | If casing depth is >10 cm, check whether the light source position is properly adjusted or brightened. | Hotspots when too close; light loss when too far. | □ Pass □ Light-to-Panel Distance Issue | |
| III. Enclosure Interior | 6. Reflective Coating | Confirm that the inner wall is coated with high-reflectivity white paint. | Reduced light efficiency and dark edges. | □ Pass □ Internal Reflective Issue |
| 7. Internal Light Obstruction | Check if reinforcing ribs or support columns block light; check for cable clutter or coiling. | Localized Strip Shadows. | □ Pass □ Internal Obstruction | |
| IV. Material Quality | 8. Light Uniformity | Check whether a diffuser panel (LGP) is used instead of a standard transparent panel. | Visible LED Point Sources. | □ Pass □ Wrong Panel Selection |
| 9. Panel Consistency | Check panel thickness uniformity and color variation. | Blocky shadows caused by uneven light transmission. | □ Pass □ Panel Quality Issue | |
| V. Power Supply | 10. Voltage Drop Control | Check if the number of series connections is excessive and measure the end voltage. | Bright at the front, dim at the end. | □ Pass □ Excessive Series Connection |
| 11. Power Supply Loading | Ensure load is kept within 80% of rated power capacity. | Hazy and dim overall illumination. | □ Pass □ Insufficient Power |
Take Away
The reasons for the shadow issue of LED illuminated signs may seem numerous and complex at first glance. However, if you take the time to study them carefully, you will find that these factors can be summarized into two aspects:
- Material Selection Issues: For instance, poor-quality LED light sources, insufficient power supply, or incorrect selection of LED modules;
- Manufacturing Process Issues: Such as improper layout of LEDs, lack of reflective coating, poor internal obstruction control, or excessive series connection of LEDs;
If handled carefully, almost all of the above issues can be avoided during the manufacturing stage.
As a veteran expert in this industry, FT Signage not only possesses rich experience in manufacturing LED illuminated signs but also maintains strict standards for material selection. By preventing shadow problems at the source, we provide customers with satisfying products and a perfect brand presentation.
Should you have any customization needs or run into any problems, please feel free to contact us.
