Many people may not have noticed it yet, but Apple uses a small optimization to improve the battery life of the MacBook when the power adapter is not connected.
It’s known that you can turn on the option “Dim the monitor slightly when using battery power” under System Preferences > Power Saving. This will automatically darken the screen – and use less power.
What’s interesting to note, though, is that the Mac does that unasked for anyway. Even if you leave this option unchecked, the Mac slightly reduces the display brightness when you remove the power adapter. So there seem to be two levels of dimming, one of which is simply always applied.
Lower display brightness – longer battery life
However, the reduction is so fine that we only noticed it in a room that is illuminated in the evening – and you have to look carefully when changing. When the display brightness was half as bright and when the power supply was removed, the brightness dropped minimally. We then tried to disable this function in the system settings – but it was already off. You can try it yourself by plugging in and unplugging the power supply: the change is minimal and often only visible when you know it. In daylight it is not noticeable. But apparently this small reduction in brightness brings valuable battery life.
Apple is known for using very clever energy saving mechanisms. This sparing use of the display brightness seems to be part of it.