It is the backlight of The MX Keys series. I have some different ideas. Now it turns off too fast. Having to constantly wave on your keyboard doesn't seem particularly wise. I am AGAINST keeping it on all the time because users will have to manually turn the keyboard off every night. Unless it is capable of detecting certain gestures so turning it off wouldn't be a burden. Some other ideas to solve this problem: i. sensor sensitivity alteration to make the keyboard more aware of hand movements; ii. only turn off the backlight when there's no movement for a period of time, and allow users to set this time. Batterylife will be an issue. Fortunately, there are teardown videos, where I find there's plenty of space to double the battery. And battery tech has advanced quite a lot so you can get batteries with higher density and efficiency.

Additional suggestion: for the mechanic keyboard, try to make it more like the none-mechanic ones. That is, don't allow the backlight to be visible from the side of the keys and let the light out only through the characters and signs.