You can get hPowerReq by calling SetPowerRequirement.

    backlightHandle = NativeMethods.SetPowerRequirement("BKL1:", DevicePowerState.D0, 1, null, 0);

static extern int SetPowerRequirement(string DeviceName, DevicePowerState State, uint dwDeviceFlags, string Name, ulong Reserved);

Declare Function SetPowerRequirement Lib "coredll.dll" Alias "SetPowerRequirement" (ByVal DeviceName As String, ByVal state As DevicePowerState, ByVal dwDeviceFlags As UInteger, ByVal name As String, ByVal Reserved As ULong) As Integer

          SetPowerRequirement("BKL1:",DevicePowerState.D0,POWER_NAME,null,0);