Most, if not all, Windows laptop computers will dim their screens after a configurable time duration. After an additional time duration, the screen will turn off completely. These settings are configured via the Power Options or Power Management control panel in Windows. Some computers even let you configure the percentage to dim at each stage.

What about external monitors connected via HDMI? Can they be dimmed automatically by Windows after a certain amount of time has passed?

What I've seen on laptops with external monitors is that the laptop screen will dim, but the external monitor will either be on on off. Is there a way to dim the external monitor at the same time the laptop's screen is dimmed?

To clarify, I'm not talking about the dimming of the display by using the screen's brightness controls. I'm talking about dimming during the power management sequence during periods of inactivity.

BTW, some external monitors shows how much power they are using. Reducing the brightness can reduce the power consumption by as much as 85%!


DisplayPort and even DVI implement the VESA MCCS standard for controlling the settings of a connected display device, and can be controlled over the AUX channel on DisplayPort and DDC/CI on DVI. MCCS essentially allows control of the same settings using the monitors on screen display, except without the on screen display.

MCCS implements VCP (virtual control panel) codes that tell the monitor to do something the OSD can. VCP code 0x13 sends a backlight level signal to the monitor. The values are between 0 and 255, and are interpreted by the monitor to its internal granularity, with a value of 0 being the lowest, and 255 being the highest.

Finding a video card and monitor that support MCCS however is not difficult. My ATI video card supports it, as does my old 2006 Samsung monitor (MCCS 0.20) over DVI, however my Dell monitors (DVI and DisplayPort) had DDC/CI disabled, even though they support MCCS 2.1. Enabling the setting allowed the backlight level to be controlled on all my monitors.

Since I keep my backlight levels at around 5%, dimming them through the backlight setting is not effective. Dimming can be done in software through the OS/video card brightness setting in addition to the backlight level.

When it comes to Windows supporting these settings through the power control panel, I do not know if that is possible in Windows 7, but may be supported in later versions of Windows. It is certainly possible at the hardware level, and through the video card drivers.

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  • Great info... thanks! What about HDMI? – RockPaperLizard May 10 '15 at 12:13
  • @RockPaperLizard HDMI should, even VGA if the monitor and video card support it – Richie Frame May 11 '15 at 4:26

It's not possible with external monitors, because they are connected through VGA or other port, which doesn't support dimming. The laptop can only turn the screen off by cutting the video output to the VGA port.

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  • Thanks. Is that true for HDMI and DVI as well? – RockPaperLizard May 10 '15 at 10:25
  • No, external monitors have their own brightness system. Maybe some new models and standards will have this. – redbeam_ May 10 '15 at 10:40

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