Why the screen dims on Xiaomi Redmi 9: the reasons and how to return the brightness

Xiaomi Redmi 9's screen suddenly dim and the picture is no longer juicy? The problem is more common than it seems -- and the matrix isn't always to blame. 60 percent of the time, the culprit is system settings or software glitches that can be fixed without repair. But how do you tell a harmless glitch from a serious breakdown?

In this article, we’ll look at all the possible reasons why the Redmi 9 screen (including the Redmi 9A/9C/9T) dims on its own or after a fall. You’ll learn how to check for autobrightness, reset your display settings, diagnose hardware malfunctions—and when to bring your phone to service. And we’ve collected exclusive data on typical screen “diseases” that you won’t find in the official manuals.

We warn you right away that if the dimness is caused by a hit, a fall, or a smear, it's likely that the backlight or the plume of the matrix is damaged, and in this case, any software manipulation is useless, you need diagnostics in the service, but if the screen gradually turns pale without mechanical damage, the chances of "treatment" at home are high.

And one more nuance: Redmi 9 is equipped with IPS LCD- screen with LED- backlight, which degrades over time. If the phone is larger than 2-3 years, dimness can be a natural wear and tear, but even then there are ways to temporarily improve the picture — that’s covered in the hardware reasons section.

1.Autobrightness and adaptive backlighting: why the screen itself dims

The most common reason is a misfired light sensor or a misaligned autobrightness setting. The default MIUI system tries to save battery power by automatically muting the screen in dark rooms. But sometimes the algorithm works inadequately: for example, on a sunny day, the display suddenly dims, as if you were in a basement.

How to check:

🔍 Open Settings → Display → Brightness and turn off the "Auto-Brightness" slider. If the screen gets brighter immediately, the sensor is a problem.
📱 Reboot your phone. Sometimes the glitch of auto-brightness disappears after the reboot.
🌡️ Check the light sensor: close the area next to the front camera (where the sensor is) with your finger and flash a flashlight. If the brightness does not change, the sensor is defective.

If the sensor is working, but the autobrightness still glitch, try resetting the display settings:

Settings → System → Reset settings → Reset display settings

⚠️ Warning: Redmi 9 with MIUI 12.5+ has a bug that can keep autobrightness at a minimum after the upgrade, and only a full phone reset or firmware rollback will help.

📊 How often do you use autobrightness on your smartphone?

Constantly.

Only in the daytime.

Shut it down forever.

I don't know what it is.

2. Energy saving modes: hidden brightness limits

MIUI aggressively saves battery power, and sometimes it results in forced screen dimming. Even if you haven't manually activated the power saving mode, the system can turn it on automatically when the charge level is low (usually below 15%).

Where to look for settings:

🔋 Settings → Battery and performance → Power saving mode. Turn it off if it's active.
⚡ Settings → Battery and performance → Battery settings → Screen energy saving. You can turn off automatic dimming here.
📊 Some firmware has a hidden Ultra Power Saving mode that limits brightness to 30 percent. To turn it off, hold the power button and select "Exit Power Saving Mode."

Especially insidious is Super Standby, which is activated at night, and it not only dims the screen, it turns off the background.

Settings → Battery and performance → Battery settings → Super standby

⚠️ Warning: Redmi 9 with MIUI 13 has a bug where energy-saving modes can turn on spontaneously after an upgrade. If brightness is reset every day, try rolling back the firmware or installing custom software (e.g., Pixel Experience).

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To quickly check if the energy-saving mode is to blame, connect your phone to charge, and if the screen is brighter, the problem is with the battery settings.

3. Software failures: when firmware is to blame

If the screen dims periodically (for example, after rebooting or opening certain applications), the software is to blame.

🐛 Glitches of the graphics driver (especially after the MIUI update).
📱 A failure in SurfaceFlinger, the system process responsible for displaying the interface.
🦠 A virus or malware that manipulates display settings.

How to diagnose:

Launch your phone in Safe Mode (hold the power button → Safe Mode) If the screen is normal, the third-party app is to blame.
Check the system logs for display driver errors. To do this, install the App Logcat Reader from Google Play and find records with DisplayManager or SurfaceFlinger tags.
Update your firmware to the latest version or roll back to a stable build if failures started after the update.

If the problem is in the driver, temporarily help reset the cache of the graphics subsystem:

Settings → Applications → Application Management → Three points (menu) → Show system → SurfaceFlinger → Storage → Clear cache

List of firmware with a dull screen bug

On Redmi 9, the screen dimming problem was massively manifested in the following versions of MIUI: - MIUI 12.0.8-12.0.12 (bug with autobrightness after sleep) - MIUI 12.5.1-12.5.3 (forced brightness restriction in games) - MIUI 13.0.2 (glitch with a backlight driver) If you have one of these versions - we recommend updating or rolling back.

4. Hardware malfunctions: when without repairs can not do

If the software methods didn’t help, the problem is likely to be the hardware.The Xiaomi Redmi 9 has the following hardware defects:

Malfunction	Signs.	Can I fix it?
Wearing LED-lighting	The screen fades gradually, especially around the edges. The colors become dirty.	Replacement of the matrix only (cost ~2500–3500 ₽).
Oxidation of the illumination plume	The screen dims when the phone is tilted or heated, and sometimes vertical stripes appear.	Cleaning/replacement of the plume (~1500–2000 ₽).
Damage to the lighting controller	Brightness jumps or is fixed at a minimum level, artifacts in the form of flickering are possible.	Replacement of the motherboard or soldering of the controller (~3000–5000 ₽).
LED tape detachment	Dim spots or uneven backlighting (for example, one corner is darker).	Tape gluing (~2000 ₽) but often recurs.

Critical: Redmi 9 often fails the backlight controller chip (U701) that powers the LED- tape. Replacing it requires a soldering station and costs ~1000-1500 ₽, but 80% of the services offer to replace the entire board – it is unreasonably expensive!

How to check for hardware malfunction:

🔦 Light the flashlight on the screen at an angle, and if you can see it clearly, the problem is the backlight.
🔥 Heat the phone with a hair dryer (no higher than 60 °C!) If the screen is temporarily brighter, it's the plume or soldering that's to blame.
🛠️ Disassemble the phone and check the backlight plume for oxidation (green plaque) or microcracks.

⚠️ Warning: If the screen only dims when charging, the problem is the backlight power supply on the motherboard. This is a typical Redmi 9 "disease" after a year of use. Not to be confused with the energy-saving mode!

5.Damage to the matrix: when dullness is the first bell

The Redmi 9 screen uses a IPS LCD- matrix that degrades over time. If the phone is older than the 2 years, dimness may be a sign:

💡 Backlighting resource production (LED-diodes lose brightness after ~20,000 hours of operation).
🔳 Polarization filter layers (the screen becomes cloudy as if covered with film).
🧲 Demagnetization of liquid crystals (colors fade, contrast drops).

How to extend the life of the matrix:

⚡ Do not use brightness at maximum for more than 10 consecutive minutes.
🌡️ Avoid overheating (do not leave your phone in the sun or near the battery).
🔄 Once a month, “accelerate” the matrix: set the brightness to 100%, open the white image for 5 minutes, then return the settings to normal.

If the matrix is already worn out, temporarily improve the picture will help:

🎨 Use high contrast themes (e.g., AMOLED Black in theme settings).
🔧 Increase the gamut through the engineering menu (type ##36446337#, then select Gamma Correction).
🖥️ Connect to an external monitor via USB-C → HDMI (if you need to work urgently).

Check the screen for the uniformity of the backlight (open the white image)

Click on the corners of the display – if there are divorces, the matrix has detached

Connect your phone to your PC: if the computer picture is normal, the problem is in the display

Check if the screen dims when tilted (a sign of plume damage)

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6. App impact: Who steals your brightness?

Some programs can force the screen to turn down even if you don't notice it, and most often, it's the fault of:

📖 Readers and books (e.g. Moon+ Reader or FBReader have their own lighting settings).
🎮 Games (especially PUBG Mobile or Genshin Impact, which limit brightness to save battery life).
👁️ Applications for vision protection (f.lux, Night Shift or built-in MIUI Read Mode).
🔒 Nova Launcher (POCO Launcher) can reset display settings.

How to find the culprit:

Open Settings → Applications → Permissions → Change system settings. This will be all programs that have access to brightness.
Run your phone in Safe Mode and watch the screen for 10-15 minutes. If the brightness does not change, it is the fault of third-party software.
Remove newly installed apps one by one, checking brightness after each.

Especially insidious are applications that overlap over other windows (like Blue Light Filter or Lux Auto Brightness), which can block system brightness settings to detect them:

Settings → Special features → Applications with special access → Overlay over other applications

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If the screen only dims in certain apps (like Instagram or Chrome), the problem is not with the phone, but with the software settings. Check the Dark Theme or Energy Saving settings inside the program.

7.When to contact the service: checklist before repair

If you’ve tried all the techniques, but the Redmi 9 screen is still dim, it’s time to get ready for a visit to the service center.

Reset all settings to factory (Settings → System → Resetting)

Test the phone with a different charge and cable (sometimes the problem is the power supply)

Try other firmware (for example, custom software based on Android 11)

Check the screen for physical damage (cracks, dents, traces of moisture)

Make sure the case isn’t the problem (some silicone cases press on the backlight plume)

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The cost of repair depends on the diagnosis:

🔧 Replacement of the backlight plume: 1500–2500 ₽.
💡 Replacement of LED- tape: 2000–3000 ₽ (but often helps temporarily).
📱 Replacement of the matrix: 3,500–5000 ₽ (original) or 2000–3000 ₽ (analogue).
🔌 Motherboard repair (replacement of the lighting controller): 2000–4000 ₽.

Warning: In 30% of cases, the masters offer to replace the entire display module, although the problem is solved by cleaning the plume or soldering the chip.

⚠️ Warning: If you are offered to replace the matrix with a Redmi 9 for less than 2000 ₽, most likely it is a fake. The original display is labeled Tianma TM1670 or BOE NT36525B — check with the wizard.

FAQ: Frequent questions about Redmi 9's dim screen

The screen got dim after the fall.

It's probably the backlight plume or the LED- tape itself that's damaged. Check if there's a crack or a spider on the screen (if so, just a matrix replacement); if the phone's brightness changes when it's tilted (if so, a plume problem); if you see the image under the flashlight (if so, the backlight is faulty); 90% of the time, after a fall, only repairs help; Average cost: 2000-4000 ₽.

Can I replace the screen lighting myself?

Theoretically, yes, but in practice, it's extremely difficult: You need special tools (suction cups, mediators, soldering irons); the risk of damaging plumes or matrix during disassembly; LED- tape is glued to double-sided tape, which is difficult to remove without traces; if you don't have experience, you better contact the service; Self-substitution is often more expensive due to errors.

Why does the screen only dim in the sun?

This is normal behavior of the light sensor, but in Redmi 9 it often works incorrectly. Try: Turn off autobrightness and set the brightness manually by 80-100%. Wipe the area of the sensor (near the front camera) - it may be contaminated. Update the firmware (in MIUI 12.5 + corrected adaptive brightness algorithms). If it does not help, the sensor is faulty (replacement will cost 800-1500 ₽).

After the MIUI update, the screen became dim. How do you roll back?

If the problem has occurred after the update, try: Reset the display settings (Settings → System → Reset → Reset the display settings). Reverse the previous version via the Mi Flash Tool (instructions on the official Xiaomi website); Install custom software (for example, LineageOS or Pixel Experience).

The screen dims when the battery is low. Is that normal?

Yes, MIUI has a screen energy saving feature that forcefully reduces brightness when charged below 15%. It shuts down: Settings → Battery and Performance → Battery settings → Screen energy saving If the option is turned off but the screen still dims – check the settings of specific applications (for example, games often limit brightness when discharged).