Enable both places
Turn on DDC/CI in the monitor menu, then enable Monitor controls (DDC/CI) for that display in Display Dimmer.
Hardware brightness
Enable DDC/CI for hardware brightness
DDC/CI lets Display Dimmer control real monitor brightness when your monitor, cable path, and per-display app setting all allow it.
Test a direct cable
Docks, KVMs, adapters, USB graphics, HDR modes, and some inputs can block hardware brightness commands.
Use fallback if needed
Gamma dimming keeps brightness control available when DDC/CI is missing, blocked, or unreliable.
What DDC/CI does
DDC/CI is a monitor control feature that lets software send commands such as brightness changes to an external monitor. When it works, Display Dimmer adjusts the monitor's real hardware brightness instead of only darkening the image.
Support depends on the monitor, input, cable, dock, adapter, KVM, and graphics path. That is why DDC/CI can work on one display in a setup and fail on another.
Enable Monitor controls in Display Dimmer
Display Dimmer treats DDC/CI as a per-display setting. After enabling DDC/CI in the monitor menu, turn it on for each display you want to control with hardware brightness.
Open Settings
Open Display Dimmer, go to Settings, then choose Displays.
Choose the display
Select the monitor and turn on its Monitor controls (DDC/CI) switch.
If the brightness slider changes the monitor's real backlight after this, DDC/CI is working for that display.
If DDC/CI still does not work
- Try a direct HDMI, DisplayPort, or USB-C DisplayPort Alt Mode cable without a dock, adapter, KVM, or capture device.
- Try another monitor input, such as DisplayPort instead of HDMI.
- Open the monitor menu once, then test again. Some monitors wake the control channel only after the menu opens.
- Turn HDR off temporarily for that display. HDR often puts monitors into a separate picture mode that can ignore or block DDC/CI.
- Update monitor, dock, and GPU firmware or drivers when updates are available.
- Use gamma dimming fallback if hardware brightness remains unavailable or unreliable.
If DDC/CI works directly but fails through a dock, KVM, switch, DisplayLink adapter, MST chain, or HDR mode, the display path is probably blocking the control channel.
Frequently asked questions
What does DDC/CI do?
DDC/CI is a monitor control feature that lets a computer send commands such as brightness changes to an external monitor.
Do all monitors support DDC/CI brightness control?
No. Many monitors support it, but some do not. Docks, adapters, KVMs, USB-C hubs, DisplayLink paths, MST chains, HDR modes, and some monitor inputs can also block DDC/CI.
How do I know if DDC/CI is working?
If DDC/CI is working and Monitor controls (DDC/CI) is enabled for that display in Display Dimmer, moving the brightness slider changes the monitor's real hardware brightness. If the monitor does not respond, try a direct cable, another input, or gamma dimming fallback.
Do I need to enable DDC/CI in Display Dimmer too?
Yes. After enabling DDC/CI in the monitor menu, open Display Dimmer, go to Settings > Displays, find the monitor, and turn on its Monitor controls (DDC/CI) switch. DDC/CI is enabled per display, so repeat this for each monitor you want Display Dimmer to control with hardware brightness.
What should I use if DDC/CI still does not work?
Use gamma dimming fallback for that display. It does not change the monitor backlight, but it keeps brightness control available.
Control brightness without the monitor menu.
Use DDC/CI hardware control where supported, with gamma fallback when needed.