There are many different types of light from many different sources. Fireflies and glow worms give off light, fluorescent bulbs give off light, and matches when struck give off light. The sun also gives off light. It is an enduring light that can never fade, and that will endure until the end of time. Whenever you encounter someone who seems to be all aglow with light, you are required to determine the nature and source of the light. Light that is from God emanates from the heart, the solar plexus, radiates outward from the heart, and eventually encompasses the entire body.
The devil has sought to cover his cohorts with light so as to enable them to masquerade as angels of light and sources of truth amidst the darkness in our world. Unfortunately, because their solar plexus (the heart) is occupied by a demon (in most instances), it is impossible for light to shine forth from their heart. Instead, the light is artificially generated in skin cells. Regardless of how much light they have in other parts of the body, their hearts will always be pitch black.
The Lord God Almighty El Shaddai