How to permanently disable the light sensor on Xiaomi Redmi 9: from settings to physical locking

Why do users want to turn off the light sensor on Redmi 9 – and should they?

The ambient light sensor on Xiaomi Redmi 9 automatically adjusts the brightness of the screen depending on external conditions. In theory, this is convenient: in a dark room the screen dims, in the sun it becomes brighter. But in practice, many owners experience annoying brightness spikes when the sensor is triggered too sharply or mistakenly, for example, when the phone is tilted in the hands or when the shadow from the finger is hit.

Another common reason is battery saving: Automatic brightness control requires constant sensor operation and processing by the processor, which consumes up to 3-5% of the charge per day when used actively. Finally, some users simply prefer fixed brightness, especially if they work with graphics, video or games where stable display is critical.

However, before turning off the sensor, two key points should be considered: first, on some versions of MIUI, after turning off the automatic brightness, a manual slider disappears in the notification curtain; secondly, when the sensor is physically blocked (for example, tape), other sensors located nearby may fail.

Method 1: Turning off automatic brightness via MIUI settings

The easiest and safest method is to software disable the feature in the phone's menu.It works on all versions of Redmi 9 (including Redmi 9A/9C/9T models) with MIUI 11-14 firmware.

1. Open the settings (cog icon on the desktop).
2. Go to the Screen section (or Display in some localizations).
3. Slip on Brightness.
4. Turn off the Automatic Adjustment (or Adaptive Brightness) switch.
5. Manually set a comfortable brightness level with a slider.

If after these actions, the brightness slider disappeared from the notification panel, return it like this:

• 📱 Go to Settings. → Notification panel and status bar.
• 🔧 Select Control Panel Settings (or Quick Settings).
• 🔍 Find Brightness in the list and drag it to the active area.

The brightness slider appeared in the notification curtain |

The brightness of the screen stopped spontaneously changing |

In the display settings, the tick "Automatic adjustment" is removed |

The phone does not overheat when manually adjusting the brightness-->

⚠️ Note: On some custom firmware (e.g. Pixel Experience or LineageOS), the Auto Adjustment option may be in the Settings section. → System system → Gestures → If you don't find it, check the firmware version in Settings. → The phone.

Method 2: Use of an engineering menu (for power users)

If a standard shutdown doesn't work (for example, the brightness still jumps), you can lock the sensor through an engineering menu, which requires caution, since incorrect changes can lead to malfunctions in the screen.

Instructions for Redmi 9:

1. Open the Phone app and enter the combination: ##36446337## (this is the code to access the LCD Test menu).
2. In the menu that opens, select Light Sensor.
3. Click Disable or uncheck Auto Brightness.
4. Save the changes and restart the phone.

Alternative code for new versions of MIUI:

##6484##

(Mention MTK Engineer Mode if the phone is on a MediaTek processor)

Method 3: Lock the sensor physically (scotch, sticker, case)

If the software didn't work, you can glue the light sensor down, and it's located at the top of the screen, next to the front camera, and the exact location depends on the model.

• 📱 Redmi 9 (standard): sensor to the right of the camera (when looking at the screen).
• 📱 Redmi 9A/9C: sensor to the left of the camera, next to the speaker.
• 📱 Redmi 9T/9 Power: sensor in the center of the upper frame.

Locking materials:

• ✔️ Black seal (not allowing light, easily removed).
• ✔️ Sticker from the old one SIM-map (thin, does not interfere with the proximity sensor).
• ❌ Scotch or transparent tape (may pass infrared radiation).
• ❌ Paint or marker (risk of damaging the oleophobic screen covering).

Yeah, it helped.|

Yeah, but the effect was temporary.|

No, I'm afraid I'll damage my phone.|

I tried it, but the sensor still worked.-->

⚠️ Attention: On Redmi 9, the light sensor is combined with the proximity sensor (turns off the screen during a call). If you tape it completely, you can have problems with the sensor during conversations. The solution is to use a sticker with a small hole (0.5 mm) for an infrared sensor.

Method 4: Disconnect via ADB (for advanced users)

If you have access to USB debugging (ADB), you can turn off the sensor at the system level, which is reversible and doesn't require root rights.

• 🖥️ A computer with installed Xiaomi drivers and ADB Tools.
• 📱 Included debugging by USB on the phone (Settings) → The phone. → Version. MIUI — Tap 7 times, then return to the additional → For developers → Debugging by USB).
• 🔌 USB-cable (preferably original).

Step-by-step:

1. Connect the phone to the PC and confirm the debugging permission.
2. Open the command line (Windows) or terminal (macOS/Linux) in the adb folder.
3. Enter the command to check the connection: adb devices (should appear serial number of your Redmi 9).
4. Turn off automatic brightness: Adb shell settings put system screen_brightness_mode 0
5. Set a fixed brightness (for example, 50%): adb shell settings put system screen_brightness 128 (significance 0 before 255).

To return automatic adjustment, use the command:

adb shell settings put system screen_brightness_mode 1

💡

If the brightness changes after the ADB shutdown, check the settings of the Google app (on some firmware it override system settings). Go to Settings → Apps → Google → Storage → Clear data and restart the phone.

Method 5: Remove the sensor software (requires root rights)

For users with unlocked bootloader and root access, there is a radical method of disabling the sensor at the kernel level.This will permanently remove the automatic brightness feature, but can lead to unstable MIUI operation or update errors.

Instructions:

1. Install a file manager with root access (such as Root Explorer or Solid Explorer).
2. Go to /system/etc/sensors or /vendor/etc/sensors
3. Find the file. light_sensor.conf (or als_ps_config.xml).
4. Rename him in light_sensor.conf.bak or remove.
5. Reboot the phone.

After that, the sensor will stop working, and the settings will disappear, "Automatic adjustment." Importantly, before deleting the file, back it up on your computer!

💡

Deleting the sensor system files is a last resort, and on some firmware, it can lead to a com.android.systemui error and permanent reboots, so if the phone starts to glittle after you delete it, restore the file from the backup or reflash the device.

What if the light sensor shuts down on its own?

Sometimes automatic brightness control stops working without you interfering.

If the sensor stopped working after the MIUI update, try:

• 🔄 Reset screen settings: Settings → System system → Resetting settings → Reset the display settings.
• 📥 Reverse to the previous version of the firmware through the Mi Flash Tool.
• 🛠️ Install a custom core (e.g., FrancoKernel) if the phone is rooted.

Alternatives to switching off the light sensor

Before you completely block the sensor, try these solutions:

• 🌓 Sensitivity setting: In some firmware (for example, MIUI 13) the sensor response rate can be adjusted. → Special facilities → Light sensor. → Sensitivity.
• 🔄 Custom firmware: Firmware like Pixel Experience or LineageOS offer more flexible brightness settings, including manual control without jumping.
• 📱 Lux Auto Brightness (allows you to create your own brightness profiles), Velocity (blocks automatic adjustment at the application level), Tasker (you can program fixed brightness on a schedule).
• 🛡️ Protective glass with a hole: Some glasses (for example, from Spigen) have a cutout for the sensor, but block some of the light, reducing its sensitivity.

If you are annoyed by the brightness spikes only in certain apps (like YouTube or TikTok), try:

1. Turn off autobrightness directly in the application settings (if there is such a point).
2. Add the app to the "exclusions" via Settings → Applications → Special Access → Battery Optimization.
3. Use Reading mode in MIUI (it fixes brightness at a comfortable level).

FAQ: Frequent questions about turning off the light sensor on Redmi 9