Xiaomi Redmi 9 is one of the most popular budget smartphones, but its screen is not always happy with brightness, especially in direct sunlight. If you notice that the display is too dim even at maximum settings, the problem may lie not only in the limitations of the hardware, but also in the wrong software.
In this article, we’ll look at all the ways you can brighten up on Redmi 9, from the obvious (adjusting the slider in the notification curtain) to the hidden (engineering menus and calibrating the light sensor). And we’ll also look at why the screen can spontaneously dim, and how to fix it without losing image quality. If you’ve tried standard methods and they haven’t helped, don’t be too upset: at the end of this article you’re waiting for exclusive life hacks that aren’t even written about on official Xiaomi forums.
1. Basic brightness settings: what you might have missed
So, to start with, the simplest thing is to check the standard settings, and many Redmi 9 users don't even realize that there are two independent brightness regulators in the system: one is responsible for manual tuning, and the other is for automatic adjustment to the lighting, and if they conflict, the screen can behave in an unpredictable way.
To avoid this:
- 📱 Open the Settings. → Display and find the Brightness slider. Move it to the far right position.
- 🌞 Turn off the "Auto-Brightness" option (if it's active). Sometimes the light sensor malfunctions, especially after updates. MIUI.
- 🔄 Reboot your smartphone – it will reset temporary errors of the graphics driver.
If the brightness is still low after these manipulations, the problem may be energy saving limitations. Go to Settings → Battery and Performance → Battery Mode and select High Performance. In this mode, the system will not artificially lower the brightness to save charge.
2. Checking the light sensor: why the screen itself dims
One of the most common bugs on the Redmi 9 is the illumination sensor, which is located next to the front camera and is responsible for automatically adjusting the brightness, and if the sensor is contaminated or damaged, the smartphone can mistakenly "think" that it is dark, and dim the screen even during the day.
To diagnose the problem:
- 🔦 Turn on the flashlight and shine a light on the sensor area (near the speaker), and if the brightness of the screen changes dramatically, the sensor is working, but it may be contaminated.
- 🧹 Gently wipe the sensor area with a soft wipe (do not use alcohol or abrasives!).
- 📊 Run the sensor test through the engineering menu (instruction below).
If the sensor doesn't respond to light at all, it could indicate a hardware malfunction, which is only a service center, but before you visit the workshop, try resetting the sensor software - read about this in the next section.
💡
On Redmi 9, the light sensor often fails after falls or moisture. If the smartphone falls, check it for hidden damage - even a slight deformation of the body can displace the sensor.
3. Engineering menu: hidden brightness settings
MIUI hides a lot of useful options from users, including manually calibrating the light sensor and setting the maximum brightness, and to access them, you need to go to the engineering menu, which is safe if you follow the instructions and do not change the unknown parameters.
How to open the engineering menu on Redmi 9:
- Open the phone app.
- Enter the code: ##36446337## (or #EEINFO###).
- Select the Light Sensor (Light Sensor).
- Press "Start Test" and write down the values in different lighting.
If the sensor values are very different from the real ones (for example, it shows 0 lux in daylight), reset:
- 🔧 Return to the main menu of engineering settings.
- 📝 Find the "Clear Calibration" item).
- 🔄 Reboot your smartphone.
Once reset, the sensor will be recalibrated when the autobrightness is first turned on. If the problem persists, try turning off autobrightness permanently and only use manual adjustment.
What to do if the engineering menu is not opened?
4 Developer settings: how to remove brightness limits
Android hides some options behind the developer mode, which allows you to turn off the maximum brightness limit that MIUI imposes to save battery, especially for Redmi 9, where the default brightness is limited to ~400 nits, although the screen is capable of more.
How to turn on the developer mode and remove restrictions:
- Go to Settings. → The phone.
- Click on the MIUI version 7 times until the notification “You are a developer” appears.
- Back to Settings → Additionally. → For developers.
- Find the option “Disable HW overlays” (or “Disable HW overlays” on some firmware).
- Activate "Debugging by" USB" and "Do not turn off the screen while charging" (this will help with testing).
After activating these options, check the brightness of the screen – it should be 15-20% above the standard maximum. However, keep in mind that this can speed up battery discharge by 10-15%. If you are critical for autonomy, use this method only when necessary (for example, outside in bright sun).
Backup of important data
Charge your phone at least 50%
Remember the current screen settings
Turn off auto-update MIUI (to avoid resetting parameters)-->
5.Firmware problems: when an update solves everything
If all of the above methods didn’t work, the problem could be a firmware bug. Xiaomi regularly releases updates to fix display management errors. For example, MIUI 12.5 had a critical bug that caused the brightness to reset after locking the screen.
How to update the firmware correctly:
- 📥 Go to Settings. → The phone. → Updating the system.
- 🔍 Click on the three dots in the upper right corner and select Download the latest version".
- ⚠️ If the upgrade weighs more than 500MB, connect to Wi-Fi and charge your phone to 80MB%.
- 🔄 After installing the update, reset the screen settings (in the engineering menu).
If automatic updates don’t work, you can try manual firmware through the Mi Flash Tool. However, this method is risky – if you make a mistake, your smartphone can turn into a “brick”. We recommend that you contact it only as a last resort and strictly according to official instructions Xiaomi.
⚠️ Warning: Don't install custom firmware (like LineageOS) for the sake of brightening. On Redmi 9, this often leads to problems with display drivers, causing the screen to flicker or display artifacts. Official global and European builds MIUI optimized best.
6. Hardware malfunctions: when without service can not do
If none of the software methods worked, the problem is likely hardware. Here are the most common Redmi 9 malfunctions that affect brightness:
| Symptoms. | Possible cause | Decision |
|---|---|---|
| The screen is dull even at maximum, the colors are faded | Failure of illumination (LED-tapes) | Replacement of lighting in the service center (~1500–2500 ₽) |
| The brightness spontaneously changes, the screen flickers | Problems with display plume or contacts | Reconnecting the plume or replacing it (~1000–2000 ₽) |
| In the sun, the screen becomes almost invisible. | The polarization layer of the matrix is damaged | Replacement of the display module (~3000–4500 ₽) |
| Brightness drops when the phone heats up | Thermodrossellation (protection against overheating) | Cleaning from dust, replacing thermopaste (~800–1500 ₽) |
If your Redmi 9 hit the water or fell, don’t try to disassemble it yourself – this can make the problem worse. In Xiaomi service centers, diagnostics are usually free, and repairs are cheaper than buying a new smartphone.
⚠️ Note: Redmi 9 often has a defect in which brightness drops after battery replacement.This is because non-original batteries do not support proper interaction with the power controller.
7.Alternative methods: when standard methods do not work
If you’ve exhausted all options but still don’t like the brightness, try these custom solutions:
- 🌈 Use dark themes and wallpaper. AMOLED-Screens (Redmi 9 is available with a lot of screens) IPS) It won't work, but the dark interface visually reduces eye strain, creating the illusion of greater brightness.
- 🔦 Set up a color profile. In Settings → Display. → Select the color scheme "saturated" - this will make the picture more contrasting.
- 📱 Install third-party brightness control software. Apps like Lux Auto Brightness or Screen Filter let you bypass the restrictions. MIUI. But they demand rights. ADB or root, which is not safe.
- ☀️ Use anti-reflective film. It doesn't increase brightness, but it improves the visibility of the screen in the sun by reducing glare.
Last tip for the most desperate: if you're willing to sacrifice the warranty, you can flash a custom core (like FrancoKernel), which allows you to overclock the backlight to 500+ nits. But this is an extreme measure, fraught with overheating and shorten the life of the screen.
💡
On Redmi 9, the default maximum brightness is limited to ~420 nits. This restriction can only be removed through an engineering menu or custom firmware, but this can reduce the life of the backlight by 20-30%.