When you sit and listen to a lecture, you direct your attention to the speaker; but you also know that you and the speaker are not the only people in the room. You have the sense that you are sitting in the middle or the inside of the space—somewhat like being immersed in water, underneath the ocean. This experience is an example of a greater awareness, which is tangible, real, and experiential. When awareness relates to experience in this way, it is called insight. Sometimes insight is spoken of in terms of light or luminosity. But this doesn’t mean something flourescent. It refers to the sense of clarity that exists in the experience of awareness.
From The Path Is the Goal: A Basic Handbook of Buddhist Meditation, pages 107–108.