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You can set the registry value HKEY_CURRENT_USER\ControlPanel\OnOff to 0 or 1 to toggle the backlight on or off. The problem is that my iPaq 3630 does not recognize the change in the registry unless I power the device off and then back on. You might try sending a WM_SETTINGCHANGE message to the desktop window, etc, to see if you can get the shell to recognize that the registry value has been changed.
Dan East
