The book defines the "clear light of reality" as: the awareness of energy transformations with no imposition mental categories.
It claims that if you recognize the clear light you can experience a sort of bliss, that in the West many call illumination.
The clear light is not a literal light but may appear that way to some individuals. I have seen many visual symbols in art that seem to represent this "clear light". One great example I think most people have seen is in the movie The Matrix. The actual matrix code, the green symbols is actually symbolic of this clear light of reality. In the movie Neo sees the code when he realizes he is "The One". Suddenly everything changes to code and he is able to let go of the program that is the matrix and see that it is all one code. He becomes, in context of the movie, illuminated. He allows his mind to let go of how real the computer program seemed consciously.
Another piece of art that I see this symbolism in is a video by the band Tool for the song Vicarious. It shows a human like figure looking at and touching a large clear rectangular three dimensional object and seeing their own reflection. Eventually the object cracks with what seems to be light.
That video seems to have a theme of a human realization, of conscious beings looking and looking to see what is there, to see what is everywhere and they keep seeing themselves. It keeps seeing the self repeated everywhere throughout eternity. Part of the video is from Alex Greys Godself painting, brought to life.
https://www.cosm.org/blog/vicarious-music-video/
To understand the teachings about the clear light in the way the book intends, one must read the book and study it and use it in their experiences. Here I will share a very interesting analogy that you may have heard some of...it likens the experience of ego death to learning how to swim:
"At this point, it is necessary to inject a word of benign warning. Reading this manual is extremely useful,
but no words can communicate experience. You are going to be surprised, startled and delighted. A person
may have heard a detailed description of the art of swimming and yet never had the chance to swim.
Suddenly diving into the water, he finds himself unable to swim. So with those who have tried to learn the
theory of how to experience ego-loss, and have never applied it. They cannot maintain unbroken continuity
of consciousness, they grow bewildered at the changed condition; they fail to maintain the mystical ecstasy;
they fail to take advantage of the opportunity unless upheld and directed by a guide. Even with all that a
guide can do, they ordinarily, because of bad karma (heavy ego games) fail to recognize the liberation. But
this is no cause for worry. At the worst, they just slip back to shore. No one has drowned, and most of
those who have taken the voyage have been eager to try again."