Set the display brightness from a Win32 application

BrightnessHelper.cs

public static class BrightnessHelper
{
	public static void SetBrightness(uint brightness)
    	{
    		if (brightness > 100)
        	{
        		throw new ArgumentOutOfRangeException("brightness");
        	}

        	// get handle to primary display
        	IntPtr hmon = NativeMethods.MonitorFromWindow(IntPtr.Zero, NativeMethods.MONITOR_DEFAULTTO.PRIMARY);

        	// get number of physical displays (assume only one for simplicity)
        	int num;
        	bool success = NativeMethods.GetNumberOfPhysicalMonitorsFromHMONITOR(hmon, out num);
        	NativeMethods.PHYSICAL_MONITOR pmon = new NativeMethods.PHYSICAL_MONITOR();

        	success = NativeMethods.GetPhysicalMonitorsFromHMONITOR(hmon, num, ref pmon);

        	uint min, max, current;
        	// commonly min and max are 0-100 which represents a percentage brightness
        	success = NativeMethods.GetMonitorBrightness(pmon.hPhysicalMonitor, out min, out current, out max);

        	// set to full brightness
        	success = NativeMethods.SetMonitorBrightness(pmon.hPhysicalMonitor, brightness);
        
        	success = NativeMethods.DestroyPhysicalMonitors(num, ref pmon);
	}

   	private static class NativeMethods
   	{
                [DllImport("Dxva2")]
                [return: MarshalAs(UnmanagedType.Bool)]
                internal static extern bool GetMonitorBrightness(IntPtr hMonitor,
                    out uint pdwMinimumBrightness,
                    out uint pdwCurrentBrightness,
                    out uint pdwMaximumBrightness);

                [DllImport("Dxva2")]
                [return: MarshalAs(UnmanagedType.Bool)]
                internal static extern bool SetMonitorBrightness(IntPtr hMonitor, uint newBrightness);

                [DllImport("Dxva2")]
                [return: MarshalAs(UnmanagedType.Bool)]
                internal static extern bool GetNumberOfPhysicalMonitorsFromHMONITOR(IntPtr hMonitor, out int numberOfPhysicalMonitors);

                [DllImport("Dxva2", CharSet = CharSet.Unicode)]
                [return: MarshalAs(UnmanagedType.Bool)]
                internal static extern bool GetPhysicalMonitorsFromHMONITOR(IntPtr hMonitor, int physicalMonitorArraySize, ref PHYSICAL_MONITOR physicalMonitorArray);

                [DllImport("Dxva2", CharSet = CharSet.Unicode)]
                [return: MarshalAs(UnmanagedType.Bool)]
                internal static extern bool DestroyPhysicalMonitors(int physicalMonitorArraySize, ref PHYSICAL_MONITOR physicalMonitorArray);

                [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
                internal struct PHYSICAL_MONITOR
                {
                    internal IntPtr hPhysicalMonitor;
                    //[PHYSICAL_MONITOR_DESCRIPTION_SIZE]
                    [MarshalAs(UnmanagedType.ByValTStr, SizeConst = 128)]
                    internal string szPhysicalMonitorDescription;
                }

                [DllImport("User32")]
                internal static extern IntPtr MonitorFromWindow(IntPtr hwnd, MONITOR_DEFAULTTO dwFlags);

                internal enum MONITOR_DEFAULTTO
                {
                    NULL = 0x00000000,
                    PRIMARY = 0x00000001,
                    NEAREST = 0x00000002,
                }
	}
}

can you kindly tell why this code does not work on laptops??? it works fine on desktops and all in one but it does not work on laptops.

For laptops you can use:
https://github.com/mbahrami/LaptopBrightnessControl/blob/master/SetBrightness.cs