how do we see light in dreams when our eyes are closed ?

You only "remember" that light, after you have opened your eyes...
But, I heard this story that because of the chemical/electrical crossing of a synapse, light is produced...Plus, you build an electrical charge, so if at rest, this charge releases, why not?
For whatever its worth.
But ya, Ive thought about it much....But as with color, you only see the color from your dreams, when your eyes have opened.

your dreams have nothing to do woth light and everything to do with your imagination. ex. Can you imagine being in a bright room if your eyes are closed in the dark?

yes i can sit here with eyes open or closed and imagine a brightly lit room,but i still cant "see" it,i can only think of it...but there is light in dreams ,the unearthly light of another world???

Your consciousness is able to perceive sights and sounds and even touch at many levels, not only the physical.

Well, as you speculated in your original post, the answer is astral planes. All dreams take place in the astral planes, though most people never learn to be conscious in that state. Some learn lucid dreaming, and a few move on to real astral projection.