I have these lights too, usually violet/indigo glowing almost neon looking. They tend to originate at my brow or forehead and then they travel away from me. One after another. I think it could be thought forms, or possibly just energy. If I focus I can change the color and then I direct it to others for healing, even at long distances. It is something I am learning, it is amazing!

And I agree it is not just light receptors, because I often meditate in darkness, and once they start I can see them with my eyes open too!