Blavatsky describes the Astral Light as a region of illusion [quoted in Farthing, p.92].
"Our Astral Light is ...the Linga Sharira [subtle body] of our earth; only instead of being its primordal prototype...it is the reverse. Human and animal bodies grow and develop on the model of their archetypal Doubles, whereas the Astral Light is born from the terrene emanations, grows and develops after its prototypal parent, and in its treacherous waves everything from the upper planes and from and from the lower solid plane, the earth,...is reflected reversed. Hence the confusion of its colours and its sounds in the clairvoyance and clairaudience of the sensitive who trusts to its records, be (he)...a Hatha yogi or a medium..."
"The Astral Light is that which mirrors the three higher planes of consciousness, and is above the lower, or terrestrial plane; therefore it does not extend beyond the fourth plane [Kama-Manas] where, one may say, the Akasha begins...."
The study of this one plane would require a whole book in itself, so perhaps we better leave it off now, with the above quotations as a basic description. But certainly it is in references such as these that we see the origin of widespread modern occult-theosophical idea of the "Astral Plane" as "the plane of illusion". It is interesting though to find a brief reference to what seems to be the same phenomena in the Tibetan Bardo Thodel ("Tibetan Book of the Dead") where the following instruction is given to the soul or consciousness of the deceased newly departed from its body:
"O son of noble family, after being unconscious for four and a half days you will move on, and awakening from your faint you will wonder what has happened to you, so recognise it as the bardo [intermediate] state. At this time samsara is reversed, and everything you see appears as lights and images."
The illusory, self-created nature of these visions is stressed elsewhere in text by the words:
"...the essential point to recognise with certainty is that whatever appears, however terrifying, is your own projection"
This emphasis on the subjectively-generated nature of the phenomena of the astral (or "bardo") world is constantly reiterated by other clairvoyants, like the Theosophist Leadbeater.
A reference can also be made to Sri Aurobindo's description of the "Intermediate Zone' with it's misleading byways.