# Why does dual-layer OLED exacerbate low-brightness unevenness?

**Published by:** [wangmingqing](https://paragraph.com/@wangmingqing/)
**Published on:** 2024-08-17
**URL:** https://paragraph.com/@wangmingqing/why-does-dual-layer-oled-exacerbate-low-brightness-unevenness

## Content

This is because the brightness of the OLED and the input current are not linearly related. Let's assume you input 50% current and the brightness is 50%; Then when 100% current is input, the brightness may be only 70%; But if you have a double-layer OLED, you can feed each layer 50% of the current to achieve close to 100% brightness. *For ease of understanding, the numbers here only represent trends. But everything has a price If we look at this picture again, you will find that OLED is not stable when driven at low current. When you want 5% brightness, a slight difference in current will cause a huge brightness change. When adjacent pixels have different brightness, when we look at the screen, it will naturally be uneven. Single-layer OLEDs already have problems, but double-layer OLEDs are even more likely to have problems. After all, dual-layer displays require only half the current to display the same brightness, making uniformity more difficult to control. So, this is why OLED uses low duty cycle PWM dimming at low brightness, because PWM allows the OLED to continue to input higher current, for example, input 50% current, but only 0.1 seconds in 1 second. When the screen is bright, 50% of the current can be used to achieve 5% brightness, which naturally avoids the instability problem of low-current driving. *For ease of understanding, the numbers here only represent trends. Therefore, the unevenness of MatePad Pro 12.2 is not at all caused by "the use of low-frequency PWM", but the lack of low-frequency + low duty cycle for eye protection. How big is the difference? I've posted this before: In fact, it is to force the original low-frequency PWM dimming to DC. The result is obvious, it is a yin and yang screen + a rag screen. Is there any solution? 1. Change to low frequency + low duty cycle PWM and solve the problem immediately. 2. Lock the brightness and limit the minimum brightness to a higher range

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