Why does a full color LED display turn cyan (color distorted)?
March 30, 2022
Some customers will find in daily operations that the full-color LED display sometimes appears cyan, which is a color distortion phenomenon. This often happens when we put the display in full white.
To figure out what is the key issue, we need to have a basic idea - the cyan cast is mostly caused by thermal effects. So what is thermal effect? Literally you can easily get the answer, thermal effect refers to overheating of the LED screen and its internal components.
Especially with the pixel pitch of LED modules, the density of LED lamp beads and internal components has been increasing, causing the internal accumulation of overheating, and sometimes this color distortion occurs.
Why does the LED full-color display turn cyan?
The reason why the screen displays cyan and not other colors in this case is mainly the structure of the LED display.
We all know the concept of RGB - red, green, and blue, and an LED lamp bead of an SMD LED display will contain these three colors, which we call the three primary colors of human beings.
If we only want to display green, then this LED lamp bead will only display green; if we want to display only red, then the LED lamp bead will only display red, and if we want to display all white, the three primary colors will be on at the same time.
Now you may have some ideas of your own - why does the screen sometimes turn cyan? That's probably due to "subtracting red", because when we mix green and blue, we get cyan!
A very simple idea, right? Now you understand that the cyan color is due to an imbalance of the three primary colors.
But why do we get "minus red" instead of other results? What effect does temperature have on the three colors?
When will we "reduce red"?
As can be seen from the figure below, the output efficiency of red light is the most sensitive to the environment, followed by green, and finally blue. Luminance output efficiency is the value of LED lamp beads at a given temperature.
In this graph, we can see that when the temperature exceeds 25°C, the output efficiency of red light decreases rapidly, while the output efficiency of blue and green light is relatively moderate.
Therefore, we can draw two conclusions:
(1) As the temperature increases, the brightness of the LED lamp beads will decrease.
(2) The brightness loss of the three primary colors is different, and the red light loss is the largest.
This is the key point behind color distortion - like we mentioned before, when there is less red light, we may end up with cyan.
How to deal with the blue color of the full color LED display?
Before talking about this part of the topic, we need to figure out which elements will affect the brightness of LED lamp beads.
There are two factors related to this, one is the output efficiency of the brightness, which we have discussed before, and the other is the actual current.
Actual current = peak current * brightness output efficiency * brightness percentage
Here we will list the three factors that determine the actual current - peak current, luminance efficiency and the percentage of light of different colors (brightness percentage).
The peak current is related to the output current of the driver chip. The smaller the resistance, the greater the peak current, or the higher the current gain, the greater the peak current.
You might be wondering, could we change the actual current by changing the output current and current gain of the driver chip to control the peak current? Unfortunately, we don't have good control over the resistance and current gain, and can only target one area, not a single LED bead.
And, if the temperature changes again, we will need to adjust the specs again. Therefore, this method is not recommended.
Luminance output efficiency
Luminance output efficiency is the proportion of time the lamp bead is lit in one second. If you adjust this value, it means that all three primary colors will be adjusted at the same time. So this way doesn't work.
Changing the brightness percentage means changing the ratio of red, blue, and green light. When the full-color LED display becomes cyan, the red light ratio of a single LED lamp bead can be increased or the blue-green light ratio can be decreased. This seems to be the most suitable method for us to improve the color distortion of the full color LED display, right?
However, it still doesn't account for the randomness of the surrounding environment, which means that if the temperature changes, you'll have to adjust accordingly again.
But don't worry, because the working temperature of indoor full-color LED display and outdoor LED display will be relatively stable. Turn the screen back to normal and things are less.
If the ambient temperature cannot be reduced to normal levels, thermodynamic correction would be a good option.
In this article, we talked about the reasons for the cyan color of the full-color LED display and the corresponding treatment methods. Generally speaking, the display is cyan to indicate overheating, and overheating will lead to a negative red ratio of the LED lamp beads. Therefore, this article explores the principles behind it and lays out three potential metrics.