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This video about how to add brightness Slider in all Windows. This app will show you Add increase, radius brightness slider.
Features
A volume like Slider to Change Monitor Brightness
Option to Run At Startup
If you get an error "Not Supported"
paste this Windows PowerShell
$monitor = Get-WmiObject -ns root/wmi -class wmiMonitorBrightNessMethods$monitor.WmiSetBrightness(80,10)
if the code above gives an error. then, there is nothing I can do. because WmiSetBrightness is provided by Microsoft. please don't open issue about this.
try install/update your graphic driver
Fixed
the slider will show at the nearest place to your taskbar
download: http://tenteaea.com/CGd