On the light emanating from the top of the head, sight of the Siddhas.
In plain words: By focusing deeply on the light at the top of the head, a yogi can see the Siddhas. Here Siddhas means higher spirit beings, not freed humans.
The Siddhas are beings who are a little above ghosts. When the Yogi concentrates his mind on the top of his head, he will see these Siddhas. The word Siddha does not refer to those men who have become free — a sense in which it is often used.
Namaste.
A calm guide to life, the mind and the old teachings.