Common LED Display Defects: Uneven Color

　　We see LED displays everywhere. For product designers, it’s smart to know about common defects to prevent mistakes. Many LED display defects happen during mass production because the process isn’t stable. Fixing these issues later can be really expensive.
　　That’s why it’s so important to work with a company that delivers consistent, high-quality LED displays.
　　This article explains what this defect looks like and shows three common examples of uneven LED color that product designers can learn from.

This article uses a seven-segment display to explain the problem of uneven LED color. When a seven-segment display lights up, you can see the color problem in the diagram.

Look at the picture below: the g, d, and dp segments are a different, lighter red. The b segment is an orange color. This kind of color change within a single display makes the whole thing look uneven. If you have four digits, they might not look like they belong together, which creates a visible defect.

Now, let’s look at three common examples of uneven color in LEDs.

Common Causes for Uneven Segment Color

　　Here are three common reasons why LED displays can have uneven color:

1. Uneven Brightness: The LEDs inside the display don’t have similar brightness (LED Luminous brightness), even when they get the same power. This makes some parts of the display look lighter or darker than others.
2. Uneven Color: The LEDs inside the display don’t have the same color (LED Emitting color), even when they get the same power. This can make a single number or letter look like it’s made of different shades.
3. Uneven Brightness and Color: The LEDs have different brightness and color (LED Luminous brightness and LED Emitting color), even with the same power. This is a mix of the first two problems, and it’s the most noticeable type of defect.

　　It can be hard to tell if the problem is with brightness or color just by looking at one defective display. However, if you place several bad displays next to each other, the problem becomes much easier to spot, as you can see in the picture below.

Common Phrases for Uneven LED Color

　　There are several ways to describe this problem.
For a single segment:
　　－Uneven brightness segment
　　－Uneven color segment
For a seven-segment display:
　　－Uneven brightness 7-segment
　　－Uneven color 7-segment
For a dot matrix display:
　　－Uneven brightness dot matrix
　　－Uneven color dot matrix
　　－Uneven brightness dot
　　－Uneven color dot
For an alphanumeric display (like 14- or 16-segment):
　　－Uneven brightness alphanumeric (or Uneven brightness 14-segment/16-segment)
　　–Uneven color alphanumeric (or Uneven color 14-segment/16-segment)

Visualizing Uneven LED Color

Since it’s hard to get pictures of uneven LED color (due to client intellectual property), this article uses a graphic to explain the most common examples. In the image above, the red arrows point to the areas with uneven color. Both the photo and the graphic use different shades of green to show the problem.

Three Common Examples of Uneven Color

　　Using a seven-segment display as an example, here are the three most common ways this defect appears:

1. Example 1: A single LED display has uneven color within its own segments.
2. Example 2: In a product with multiple seven-segment displays, one of the displays has a different color from the others.
3. Example 3: A single display shows multiple numbers, but they’re made from different seven-segment units that have different colors from each other.

Example 3 is the most common problem, followed by Example 1, then Example 2. Problems 1 and 2 usually happen when the LED manufacturer’s production process is unstable. Example 3 happens more often when the product designer doesn’t talk with the LED manufacturer about how the displays will be used together on the final product.

Example 1: Uneven Color in a Dual-Digit Display

　　The image above shows a common uneven color issue with a seven-segment display. The OPD-D5630(1)LR-GW is a display with two digits inside. Due to unstable manufacturing, the bottom display in the photo has uneven color.
　　－The d1, f2, and g2 segments look orange.
　　－The b1, e1, a2, and d2 segments are a darker red.
　　－The c1 segment is a pinkish-red.
This kind of color difference within the display makes the whole thing look bad, leading to a visible defect.

Example 2: Uneven Color in a Triple-Digit Display

　　Here is another common example using the OPD-T5620(1)LR-BW, which is a display with three digits. Because of an unstable manufacturing process, the display at the bottom of the photo has a color problem.
　　The segments a2 through g2 and the dp2 dot are a different color—they look orange. This makes the display look uneven and causes a visual defect.

Example 3: Uneven Color from Three Single-Digit Displays

　　This example shows an uneven color problem when a designer uses three OPD-S5660(1)LR-BW displays together to create a three-digit number. Each OPD-S5660(1)LR-BW is a single-digit display.
　　Due to unstable manufacturing, the displays in the bottom picture have a color issue:
　　　　－The a2, b2, d2, e2, f2, g2, and dp2 segments look orange.
　　　　－The c2 and g3 segments are pinkish.
　　　　－The a3, b3, c3, d3, e3, f3, and dp3 segments are a darker red.

Conclusion

　　For product designers who use LED displays, understanding common defects is key to preventing mistakes. Most LED display defects happen during mass production, and fixing them at this stage is very expensive. That’s why it’s so important to find a company that can consistently deliver high-quality LED displays.

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