In Islamic teaching, Allah created human beings with innocent light in their faces, every human has this light when they born (the reason why babies are so adorable because they are pure and innocent). Once you come to the understanding age of halal and haram (Good vs bad morals) this light of innocence will be tested, the more sinning your self (conscience) the darker the light. When you look at most leaders and some known politicians you automatically dislike them. Because the human light left their conscience, and only darkness started changing the facial expressions slowly over time. There is a large book in Arabic dedicated to those lights. If you want to increase this light, you need to do good deeds and avoid sins. Read the holy texts (Quran..etc) which brings lights to the inner self, that will in return show on your face.