While heads-up displays aren't very common for consumers — Apple's expensive Vision Pro aside — they are already a critical part of the military and medical industries. And, believe it or not, the main problem with HUDs in these mission-critical environments is not cost or even the embarrassment of looking uncool with a big gadget on your head — it's eye fatigue.
When you stare at the microdisplays inside a typical headset, the brightness and contrast remain fixed. Meanwhile, your pupils get larger or smaller based on your physiological and emotional reaction both to the content you are watching and the world around you. For example, if you see something in a movie that makes you emotional and your pupils dilate, all of a sudden the headset will seem annoyingly bright and you might be tempted to flip it off of your head.
