The human brain always works: it processes incoming sensory information and converts it into something meaningful for the people - this can be a pain on touching a hot kettle or aesthetic pleasure from the kind of something beautiful.
Our brain is so dependent on the information that it "fed" the senses, when this endless flow of information, for some reason disappears, begin to happen strange things. Spend some time in the isolation tank, and you start hallucinating - at least.
However, you can do without the camera - the same result can be achieved with a pair of very familiar subjects. Take the radio and adjust it so that instead of the station to hear a continuous hissing sound. Now take the ball ping-pong table, cut it in half and close the two halves of the eye, the tighter the better. Lie close to the radio and wait.
After a while, the brain starts to "worry" because the will not get the information from the two most important sensory organs - the eyes and ears. So, begin to generate new information itself, and he himself will interpret it.
This effect is called a ganzfeld. How bright hallucinations are, of course, it depends on the person, but they certainly will - for most people it happens in a few minutes.