Night Light is one of many useful features that developed methods to combat eye strain on different devices by reducing the amount of white light emitted from the screen.
Dark Mode is another popular solution, available natively on some operating systems such as Android. Google has been working on bringing Dark Mode to Chrome OS, and it can currently be tested by enabling the right flags. While Dark Mode has already been enabled in some Chrome OS elements, like the app drawer, the effect has not been made system-wide yet.
There are a couple of ways to notice the screen becoming dimmer and taking on a reddish hue.
Night Light's Customization Settings
Another way to turn on Night Light is from the device's Settings app. To open Settings, click on the Everything button (the one with a search icon) on the keyboard or tap the white button at the bottom left corner of the screen. Search for “settings” and click on the gear icon in the results to open the Settings app. Scroll down to Device and select Displays. Activate the toggle in front of Night Light. This method not only allows s to turn the feature on, but also makes it possible to customize how it works. s should see a color temperature slider under the Night Light toggle. Moving the slider will adjust the intensity of the tint on the screen.
Another customization option available for Night Light is the ability to create a schedule. A drop-down box is visible next to the Schedule option, and s can set a custom time for enabling and disabling the feature by selecting Custom from the drop-down menu. There is also the option to make Night Light automatically turn on at sunset and go off at sunrise. If enabled, the Chromebook will use the owner's current location for sunset and sunrise times. Alternatively, s can select Never to stop night mode from automatically being enabled on their Chromebook.
Source: Google