It happens that on laptops with Windows 10 the screen brightness changes spontaneously. It may be a thing and useful for someone, but it annoys me terribly. Moreover, the logic of this action is very strange: with the predominance of white, the brightness increases, and if there is a lot of black, it decreases, some kind of nonsense.
Turn off adaptive brightness in Windows 10
You need to open the power settings, for this click right click on the Start menu and select Power Management
Opposite the current scheme, click "Setting the power plan"
Also, the brightness can change itself when connected to the network or when powered by a battery and the charge drops to the indicated level. The screenshot shows that the value in the reduced brightness mode is set to 50%. We put 100% everywhere.
Problem with Intel graphics cards
If your laptop has a built-in Intel 4000/530 or other video adapter, and the first method did not help, then do the following. Right-click on the desktop and select "Graphics Features"
The control panel will open Intel driver HD graphics. If this is not the case, then in the search bar of the Start menu, write "intel" and select "Intel(R) Graphics and Media" in the results.
In the driver panel, select "Power Options":
The second option is to turn off "Extended battery life for gaming applications." Surprisingly, this can affect the floating brightness on the desktop.
If nothing helped
If you do not play 3D games, then you can go to the extreme measure - change the video card driver to the built-in Windows one. The method is NOT only suitable for Intel.
Device Manager (right-click on the Start menu), item "Display adapters". Here you will have Intel, AMD or whatever. Right-click on the adapter and "Update Drivers..."
In the window that appears, click "Search for drivers on this computer", then "Select a driver from the list of already installed drivers"
In the list, select "Basic video adapter (Microsoft)"
The screen may flicker while changing the driver. The laptop will not restart automatically, but it is better to do it manually. In such a simple way, we turned off all the "chips" from the manufacturer, but also lost the technological advantages. In fact, now the video card can only draw the desktop and video.
To return everything back, you need to do the same, but select the old driver in the last step. Or to a system restore point.
UPD from comments:
If it didn't help
After upgrading to Windows 10, laptops may have a problem with automatic brightness changes.
laptop screen brightness windows 10 changes automatically to low and it may annoy you.
If you're experiencing this problem, chances are you've already tried fix energy plan and change adaptive brightness value. (If so, skip directly to the end of the page to # 2 Replace video driver), if not, start from point # 1
.
1. Disable adaptive adjustment
Click right click on the "Start" "Control Panel".
AT "Control Panel" find "Power supply" or if you have a grouped display
On screen "Power" find "Setting the power plan", let's go there.
In power plan settings, click "Change Extra options nutrition".
Make sure we're setting the mode options active circuit to the right of the mode name there will be a signature [Active]. Lower the slider and find "Screen".
In the drop-down list, check the parameters we need. Enable Adaptive Brightness [Off]. (Both from the network and from the network)
If after that the brightness continues to change, you need to replace the video card driver.
2. Replace video driver
Go to "Device Manager". Click right click on the "Start"(Windows logo at the bottom right of the screen) and select the item from the drop-down menu. 
Find it in device manager Video adapter yours may be different, but most likely Intel(R) HD Graphic Family.
Click on it right click and select item. 
In the dialog box that will appear after clicking, you must select the item Search for drivers on this computer
On the next screen, select Select a driver from the list of already installed drivers
To disable the annoying brightness change, select from the list of suggested drivers Microsoft Basic Video Adapter (Microsoft) and press Further to install it. The screen may flicker as if the screen resolution is changed. 
When completed, in the Device Manager snap-in, under Video adapter you should have a Basic Video Adapter as shown. 
After that, the system should stop changing the brightness.
Automatic brightness control can be useful, but in some cases it makes sense to turn it off.
Users of Windows 8 and Windows 8.1 have repeatedly noticed that the screen of their laptop or tablet seems a bit dark.
The most common reason for this is the unsuccessful settings of automatic brightness control.
The presence of a light sensor in portable devices also does not guarantee correct display brightness. Therefore, in such cases, it is better to turn off the automation and adjust the brightness manually.
Of course, it’s not very convenient to open the settings and make adjustments every time you change the lighting level or power mode, on the other hand, you shouldn’t even consider it a job - vision and comfort during work are much more expensive. So how is it done? And this is done in an elementary way. Open and go to the "Power Options" section. By default, the balanced power mode is used.
We will need to create a new one or switch to the "Energy Saving" mode. Let's choose the second option. Click the link "Setting the power plan" and in the window that opens, move the sliders to adjust the brightness of the screen. After you select the desired brightness level, you will need to turn off adaptive adjustment. To do this, click the link "Change advanced power settings", in the window that opens, find the item "Screen" and click on the plus sign to open it.
There will be two more subsections. Select Enable Adaptive Brightness and set one or both to Off. Save the applied changes and close all windows. The display brightness should now remain at the same level. If you urgently need to change the brightness, for this purpose, Windows has useful tool- Mobility Center.
How to disable automatic brightness on an iPhone? Why does the brightness on the iPhone change by itself? Auto Brightness is a screen setting on iPhone and iPad that causes the device to automatically change the brightness of the display based on ambient light conditions. For example, in the sun or in bright light, the screen adjusts and increases the brightness for better visibility, and in a poorly lit room or outdoors at night, the brightness decreases. So the brightness on the iPhone itself changes.
Auto-brightness in iOS can also improve battery life by adjusting the brightness on your iPhone or iPad based on ambient light.
Some users turn off auto-brightness, and some leave it on on their iPad or iPhone. However, it was transferred to auto brightness from default settings display in deeper iOS settings. This led some users to think that iOS 11 didn't have auto-brightness, but in fact it was just moved.
In this article, we will explain in detail how to adjust the brightness on any iPhone.
The main brightness control is located in the Control Center, as always.
- Swipe in from the bottom edge of the screen to activate the Control Center.
- Move the brightness slider up or down to change the brightness.
Also, the brightness of the iPhone can be changed through the settings, for this, do the following:
- Go to "Settings".
- Scroll down and click on Display & Brightness.
- To change the screen brightness, move the Brightness slider.
Previously, in this section, you could turn off automatic brightness on iPhone, but in iOS 11, it.
Advanced brightness settings on iPhone and iPad
If you want to adjust the brightness in smaller steps or control the Night Mode, you need to press and hold or use 3D Touch on the brightness slider.
Here's how to increase the brightness on iPhone 6S and newer:
- Swipe in from the bottom edge of the screen to activate Control Center.
- Tap (on iPhone 6s or later) or press and hold the brightness slider to expand it.
- Move your finger up or down on the brightness slider to change the brightness of the display.
- Touch the “ Night mode” to turn it on or off.
How to enable or disable automatic brightness on iPhone?
In iOS 11, auto-brightness is now in Accessibility settings. Here's how to turn off auto-brightness on iPhone:
- Open the "Settings" app, go to "General" and then to "Accessibility".
- Select Display Adaptation.
- Locate the “Auto Brightness” setting and turn it on or off as needed.
The display adaptation settings mention that “Turning off auto-brightness can affect battery life”, especially if you increase the brightness of the device quite a bit, but then disable the auto-brightness feature to reduce it. If you're running out of battery quickly with iOS 11 or have other issues with it, then you probably shouldn't turn auto-brightness off, but instead leave it on and toggle other features like using location and background apps.
If it matters, auto-brightness used to be under Display & Brightness settings, but for some unknown reason has been moved deeper into accessibility settings in newer versions of iOS 11. Keep that in mind when using this feature on various devices with different iOS versions, since moving options confuses users and raises questions like “where did auto-brightness go?” Now you know!
Here is a video instruction - “How to disable automatic brightness on iPhone and iPad in iOS 11”:
How to turn down screen brightness on iPhone?
This technique allows you to reduce the brightness iPhone screen outside of the standard settings. It also uses deep iOS access settings to accomplish this task. If you use your iPhone or iPad at night, your eyes will thank you.
This includes steps that don't rely on a glitch in the system or clever timing. It's actually very easy to reduce screen brightness because it depends on a few simple settings that anyone can adjust.
- Open Settings → General → Accessibility.
- Go to the Zoom section and turn on the Zoom switch. You now see a Window Zoom overlay on top of the screen.
- Tap with three fingers on the screen to access an additional overlay with zoom controls.
- Click on "Zoom out" and use the slider at the bottom of the overlay to zoom in if needed.
- Click "Select Filter" and select "Low Light".
This feature may not work on newer versions of iOS.
With low light filter adjusted zoom, you can dim the screen on demand with a simple triple tap of the home button. I use this feature whenever I use my iPhone or iPad at the time I should be going to bed.
Instructions for setting the screen brightness in Lux:
Run the application, you will see the current light level, indicated by lux (lx), and the screen brightness adjustment slider. Set the slider to the most comfortable brightness and click on the chain icon, and then on the "Communication" button. The application remembered how bright the screen should be in such lighting. The rule is simple: the brighter the light around, the stronger the screen will be illuminated.
Do the same several times in other conditions: outside on a sunny day, on a cloudy day, in the evening, at night with the lights off, and so on. Now every time you unlock the screen, the application will measure the light sensor and change the brightness of the screen accordingly. The smoothness of the brightness change is indicated in the settings, there will be no sharp changes.
If you don't feel like taking measurements manually, you can go to the app's settings, select the profile editor, and restore the default values.
Lux can measure light in the background at different intervals, but this will increase battery consumption. Illumination detection can be disabled in the settings, then you will have to manually change the screen brightness with a slider. The range of brightness in Lux is higher than the standard settings - if desired, you can completely darken the screen.
Lux also allows you to adjust the screen color temperature for comfortable reading in twilight or total darkness. These settings can be applied automatically depending on the time of day or the time of sunrise and sunset. The color temperature changes smoothly.
