Disable Auto-Brightness Adjustment in Windows 8.1

When you are using Windows 8.1 on a laptop, you may well encounter different lighting conditions that make it difficult to see what is happening on screen. When light levels are low, for instance, having a screen turned up to full brightness can be uncomfortable on the eyes, and a dim screen in a bright room can make it hard to work effectively.
But if you are experiencing problems with the way screen brightness levels are being changed for you, or you just don’t like the feature, you can disable it so your screen or monitor remains at the same, constant brightness level.
Press “Windows key + C” or swipe in from the right hand side of the screen to display the Charms bar. Click “Settings” followed by “Control Panel” and then open the “Power Options” applet.

You will see that one of the available power plans is selected. To change the options relating to it, click the “Change plan settings” link

There are two sliders that can be used to adjust the brightness level that should be used when your laptop is plugged in to power, and when it is running on battery. You can configure these to your liking, but to disable level changing completely, click the “Change advanced power settings” link.

In the list of settings, scroll down to the “Display” section and click the “+” icon to expand it. Then expand the “Enable adaptive brightness” section to reveal the options.

It is possible to choose different settings depending on whether your laptop is plugged in or not. Use the two drop down menus to turn adaptive brightness “On” or “Off” as you want.

Having chosen your settings, click “OK”.
Should you decide that you want brightness to be automatically adjusted again in the future, just run through the steps again and choose the appropriate settings.