My Toshiba laptop was bought back in 2012. It works perfectly fine until a while ago, when it started to change brightness by itself. I'm sure it was not the power plan because it happens even when I'm using it.

This started happening not too long ago, when I had to use my laptop in the dark and so I adjusted the brightness to the lowest, ever since then, the brightness keeps hopping back to where it was every 2 minute or so.

I can adjust brightness using Fn+F2/F3 and it has a brightness icon with a slider under it to adjust, it disappears when I let go of the Fn and function keys. I somehow managed to get this stuck on the screen so I can observe it, no surprise, the slider hops to the left every now and then.

  • i've a question and an example, first. how is your power plans configured? and my example, i had the same problem an was because my laptop was consuming a lot of energy and charger starts to overheat so it turned off for time laps and turn again when it was cold again. weird. – Francisco Tapia Aug 31 '15 at 14:45

The above symptoms are that of the Ambient Light Sensor feature.

To disable this or make changes to the settings, go to the Advanced Section of the Windows Power Settings > Display > Auto Dim.

Check Control Panel > Power Options and select maximum performance

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Next choose change plan settings. You can set when to dim the display when on AC or while on battery.
Here, we have selected "never" for both, and have adjusted up to full brightness - this may only make sense for test purposes, or for plugged in mode. On battery, full brightness and never dimming will reduce battery run time.

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Lastly, click the blue link at the bottom to change advanced power settings...

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Scroll down to the section for adaptive brightness and click the + to expand the section. Now you can select to enable or disable this on both battery and plugged in (AC) mode. If you had already made the changes in the steps above and notice the auto dimming while on battery, toggling off on battery here should keep the display at your selected brightness levels at all times (based on your power plan settings above).

Source: https://forums.lenovo.com/t5/ThinkPad-S-Series-ThinkPad-Yoga/Random-changes-in-screen-brightness-every-few-minutes-in-Windows/ta-p/915291

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