A brightness sensor is a device that measures the amount of light in a given environment. It helps control the brightness of things such as screens, lights, or displays based on the surrounding light levels. Full definition
Many modern laptops and tablets have an ambient brightness sensor, which works similarly to the one found on smartphones and tablets. (howtogeek.com)
You'll only see this option if your device has an ambient brightness sensor. (howtogeek.com)
It also has the Blue Shade feature to filter blue light, along with an auto brightness sensor, which I find very distracting but at least it can be turned off. (blog.the-ebook-reader.com)