How to set autobrightness on Xiaomi Redmi Note 9: a detailed guide

Xiaomi Redmi Note 9 is one of the most popular mid-range smartphones, still in use by millions of users, but even a few years after its release, many owners of this device are faced with a problem: the screen is too dim in sunny weather, then blinds their eyes in the dark, the fault of the wrong automatic brightness control.

In this article, we'll look at not only the basic autobrightness settings, but also the hidden MIUI chips that can save battery power without losing comfort, how to calibrate the light sensor, why brightness can jump on its own, and what to do if autobrightness doesn't work at all, and how to compare the efficiency of autobrightness to manual adjustment in different use cases.

Why is the Redmi Note 9’s autobrightness not working properly?

Before you set it up, it’s important to understand why automatic brightness control can be strange. In the Redmi Note 9 (models M2003J15SC, M2003J15SS and other modifications), a complex of three components is responsible for this:

• 📱 Light sensor – located next to the front camera, measures the level of external light.
• 🤖 Algorithm MIUI — Analyzes sensor data and selects the optimal brightness.
• ⚡ Firmware and drivers – ensure the correct operation of the first two components.

If any of these elements fail, the autobrightness starts to "glue." For example, after the update to MIUI 12.5 → 13, many users complained about sharp spikes in brightness, the reason is a modified energy saving algorithm, which became more aggressive to reduce the backlight at the slightest decrease in light.

Another common problem is the contamination of the light sensor, where dust, fingerprints, or a protective glass with an incorrect cutout can distort its readings, and the result is that the smartphone "thinks" that it is dark around, and dims the screen even in bright sun.

Basic setting of autobrightness through the MIUI menu

So let's start with the simplest thing, which is to turn on and first set up auto-regulation, which is a method that's suitable for most users who don't want to dig into the engineering menu.

1. Open the Settings → Display.
2. Activate the Auto Brightness switch (or Adaptive Brightness in new MIUI versions).
3. Move the slider manually to a level that is comfortable for you – this will be the base brightness from which the algorithm will start.
4. Return to the main settings menu and go to Additional settings → Special features → Color correction. Here you can turn off Automatic Color Temperature if it conflicts with autobrightness.

Note that in MIUI 14 and later, Auto Brightness may be hidden behind the Adaptive Display option. If you don't, search by settings (the magnifier icon in the upper right corner).

Make sure there is no sprayed protective film on the screen.|Clean the light sensor with a dry napkin|Turn off power saving modes (e.g., Superbattery»)|Update your firmware to the latest stable version-->

Fine tuning through the engineering menu (for advanced)

If the standard settings don't work, you can tweak the autobrightness parameters through the engineering menu, which is a method that requires caution, but allows you to fine-tune the sensor response.

To enter the engineering menu:

1. Open the Phone app.
2. Enter the combination: ##36446337##
3. Select the Light Sensor (Light Sensor).

Here you will see the current sensor readings in lux (lx) and the reaction graph.

Warning! Do not set Min brightness below 5 - the screen will become too dim for comfortable use at dusk. Also avoid Max brightness values above 230: this will speed up battery discharge and can lead to burnout. OLED-pixels (although Redmi Note 9 uses pixels) IPS-matrix, the risk of overheating of the matrix remains).

Manual calibration of the light sensor

If the autobrightness jumps or reacts to light with a delay, the sensor could recalibrate, often after a phone falls or a poor-quality protective glass is installed, and manual calibration will help to return the exact work.

For this:

1. Place your smartphone on a flat surface in a room with uniform lighting (no direct sunlight).
2. Open the engineering menu (#36446337##) and select Light Sensor.
3. Press Calibrate and wait until the process is complete (usually 10-15 seconds).
4. Reset the device.

Critical detail: calibration should be carried out at an ambient temperature of 20-25 ° C. In cold or heat, the sensor can show incorrect values, and calibration will only worsen the situation.

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If after calibration, the autobrightness becomes worse, reset the sensor settings to the factory. To do this, select Restore Default in the Light Sensor section of the engineering menu.

Autobrightness vs. manual tuning: which is more economical?

Many users turn off autobrightness, believing that manual adjustment saves battery power, but this is not always the case.

• ⚡ Autobrightness: 🔋 Adapts to conditions, reduces brightness in the dark, which saves up to 15-20% of charge per day. ⚠️ Cons: may overstate brightness in transitional conditions (for example, in cloudy weather).
• 👆 Manual setting: ✅ Pros: predictable brightness, no sharp jumps. ❌ Cons: at constant maximum brightness, the battery consumption grows by 25-30%.

Tests show that the optimal balance is achieved by combining autobrightness with a maximum limit of 70-80%.

1. Turn on the autobrightness.
2. Manually move the slider 70%.
3. Activate Dark Mode in the display settings - this will further reduce the load on the battery.

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Autobrightness combined with a dark theme and a maximum brightness limit of up to 70% gives a better balance between comfort and autonomy.

Frequent problems and their solutions

Even when you set it up properly, autobrightness can be unstable, and let's look at the typical scenarios and how to fix them.

⚠️ Attention, if after the update MIUI Autobrightness stopped working completely, check if the permissions for the system application com.android.systemui have reset. → Annexes → Application management → Show all applications → System interface and make sure all permissions are enabled.

If none of the methods worked, try resetting the display settings:

1. Go to Settings → System and device → Resetting.
2. Select Reset Display Settings (not to be confused with a full reset!).
3. After restarting, adjust the autobrightness again.

Additional chips to save battery

Autobrightness isn’t the only way to optimize your screen performance, but here are a few hidden MIUI features that will help extend battery life:

• 🌙 Dark Mode Schedule: Set up Automatic Turning on Dark Theme with Sunset in Settings → Display. → Dark mode. → Schedule.
• ⏱️ Automatic Screen Shutdown: Reduce the time to shut down to 15–30 seconds in Settings → Display. → Sleeping mode.
• 🔄 Adaptive refresh rate: In the Redmi Note 9, the screen supports 60 Hz, but in the MIUI 13+ You can enable dynamic switching between 60 and 30 Hz to save energy (Adaptive refresh rate item).
• 📵 "On the Battery" mode: In Settings → Battery → Battery modes choose Balanced or Energy Saving – this will limit background activity and screen brightness.

Another life hack is the use of live wallpaper with dark colors. MIUI automatically adjusts the interface to the colors of the wallpaper, and if they are dark, then the system elements (panels, menus) will be less bright, which further saves charge.

FAQ: Answers to popular questions