Why do fighter pilots wear sunglasses on their helmets that cover their faces?

The main thing is to block light. The sunlight at high altitude is very strong, and it is impossible to open your eyes without sunglasses.

The second thing is to prevent high-speed airflow during skydiving and protect the pilot's face!

The visor glass of most flight helmets cannot display flight data. So far, only the F35 helmet can achieve this. Therefore, the F35 has canceled the HUD, but there are many models that can achieve it through the helmet sight installed on the helmet. For target search and aiming, its aiming halo is displayed on another separate piece of glass. For example, the Apache helicopter can realize the follow-up of the cannon and the helmet, and the Su-27 can realize the follow-up of the radar search area and the helmet!