How to Change Screen Brightness by Time of Day on Windows 10
Screen brightness is a basic control on any display. You can change it to whatever suits you or, if you have the hardware for it, you can use adaptive brightness. Adaptive brightness is fairly common and is found on desktops and mobiles alike. It changes the brightness of the screen based on the ambient light. It’s useful but you must have hardware that supports it. If you want to change screen brightness based on time of day though, you’ll find there aren’t a lot of options out there. Most apps that claim to do this are not reliable but ClickMonitorDDC is the rare exception.
This article deals with screen brightness and not the temperature of the screen. For some reason, most app developers equate screen brightness with screen temperature when they are distinctively different. If you’re looking to change the screen temperature based on time of day, use Night Light on Windows 10 or Windows 11, or use the F.lux app.
Change screen brightness based on time of day
Download ClickMonitorDDC and run it. (The original site went offline; reputable mirrors still host version 7.2.) The app runs in the system tray. Open it and click the button at the top left of the panel that appears. In the new settings window that opens, go to the Timer, Transfer, Limits tab.
On the Timer, Transfer, Limits tab, you will see a section called “auto-run command-lines.” It has support for eight different time triggers that we’re going to use to change the screen brightness. You also have the option to change the contrast and luminance but you can leave it out if you want.
First, set the time when the brightness should change. Next, enter the letter b and follow it up with the brightness level you want to set at that time (0–100). For contrast, add a space after the first command and enter c, followed by the contrast value (0–100). Finally, if you want to set per-channel luminance, you can use r, g, or l (red/green/blue, 0–255). This lets you fine-tune color channels if needed.
Sample settings
b20 c50 l200 b10 c40 b25
Add as many time triggers as you need and the app will allow. Click Apply and OK. The app will change the screen brightness for all your displays. If for some reason the app doesn’t change the brightness on one of your displays, you can use this very same app to sync brightness between them.
Important limitations & tips
- This method works on monitors that support the DDC/CI protocol (most external displays) and on laptop panels. Some monitors, cables, docks, or KVMs block DDC/CI, so scheduling may not apply to every setup. Ensure DDC/CI is enabled in your monitor’s OSD and connect the display directly where possible.
- Windows’ own features can adjust brightness dynamically for laptops or content via “Change brightness based on content.” If you see unexpected shifts, review Settings > System > Display > Brightness to disable content-adaptive adjustments while testing schedules.
- If you only need quick manual control (not scheduling), the open-source tool Monitorian provides easy sliders and can verify if your external monitors expose DDC/CI controls.
Troubleshooting
- Nothing happens on one monitor: Enable DDC/CI in that monitor’s OSD. Try a different cable (many adapters/hubs interfere with DDC). Tools like Monitorian can confirm whether a screen is controllable via DDC/CI.
- Values “snap” or don’t support contrast: Internal laptop panels often expose brightness only; contrast or per-channel luminance may be ignored.
- Night Light/HDR interaction: Night Light (color temperature) can run alongside brightness scheduling, but HDR modes or content-adaptive brightness may override your perceived luminance. Turn HDR off while testing schedules if the image looks unchanged.
- Prefer sunrise/sunset logic: ClickMonitorDDC schedules at fixed times. If you only want color temperature by sunrise/sunset, use F.lux or Windows Night Light’s scheduling. For brightness specifically, stick with fixed times in ClickMonitorDDC.
FAQs
Yes, it’s free to use, and portable builds exist. Mirrors still host version 7.2.
Yes, provided the monitor exposes DDC/CI brightness over the connection in use. Some docks/KVMs block DDC signals; connect directly if schedules don’t trigger.
ClickMonitorDDC supports powerful command lines and hotkeys; schedules can run those commands, so you can pair timed brightness with other adjustments (e.g., contrast or inputs) if your monitor supports them.
Windows offers Night Light (color temperature) and adaptive/content-based brightness on supported hardware, but it doesn’t natively schedule monitor brightness by time for external displays. That’s why a DDC/CI tool is useful here.
References & helpful tools
- ClickMonitorDDC download (mirror)
- ClickMonitorDDC command line & feature reference
- Windows: change display brightness & color (includes content-adaptive control)
- Monitorian (open-source brightness control)
What’s New in This Update
- Added a working download source for ClickMonitorDDC (original site went offline), plus a quick note on mirrors.
- Clarified command options: brightness (
b), contrast (c), and per-channel luminance (r/g/l), with current value ranges. - Expanded limitations & troubleshooting (DDC/CI requirement, cables/docks/KVMs blocking control, laptop panel constraints).
- Explained how Windows’ content-adaptive brightness and HDR can affect perceived results, and where to turn those off when testing.
- Added helpful tools: Monitorian for verification/manual control; refreshed Night Light/F.lux guidance.
Last updated: October 10, 2025
