When you are working with a multi-monitor configuration, you might notice that all the monitors except the primary monitor are a little less bright. This is usually because of the graphics card limitation and can be sometimes resolved by using a good quality graphics card such as Nvidia GeForce GT 710 with 2 GB of memory.
But another workaround is through the use of a freeware application called Dimmer. It is a portable Windows application that can help you adjust the brightness of all the monitors connected to your Windows PC. Obviously, how many monitors you can connect to your PC, depends entirely on your PC hardware and available ports. Usually, three to four monitors can be connected to a standard PC. But Dimmer can control the brightness of any number of monitors.
Dimmer employs a great workaround. Instead of controlling the brightness from zero to the maximum level, it controls the darkness from zero to the maximum level. This is why you have to first connect all the monitors and increase their brightness to the maximum. Now you can launch Dimmer and use its slider controls to change the brightness.
If you change the control for a monitor to maximum value 100, then screen becomes dark. But if you reduce it to level zero, then you can the maximum brightness. You can even turn off the control for any of the monitors. Dimmer can show the screen boundaries for your monitors as well.
Dimmer icon is placed in the notification area using which we can launch it any time. Dimmer must be launched after you have connected all the monitors otherwise it fails to identify the connected monitors. It works as promised and can even show the monitor numbers (1, 2, 3, …) so that you can identify them easily. We can make Dimmer automatically run at the startup.
You can download Dimmer from https://www.nelsonpires.com/software/dimmer.