From a wonderfully researched piece titled "The Holy Darkness: A Study of Light in Brihadeshvara Hindu Temple, Tanjore, Tamilnadu, India (1010 Ad)" by Anat Geva, Associate Professor, Texas A&M University, Department of Architecture, USA and Anuradha Mukherji, Ph.D. Candidate, Department of Architecture, the University of California at Berkeley, USA, we learn that
"The temple interiors were designed to be dark so the human eye is not distracted by the material world to let the mind enter the spiritual world of God. As seen in the Brihadeshvara Temple, natural light is introduced in progressive light quality from brightness to darkness accommodating the ritual movement of the worshiper. It is interesting to note that the reduced level of light quality in the temple also contributes to the thermal comfort of the building. Thick walls, small windows, and reduced light maintain cool and dry conditions for better thermal comfort in the hot humid climate of Tamilnadu. Thus, the Hindu worshippers are not distracted visually or thermally enabling them to focus their minds on God."
"This treatment of light ensures that by the time the pilgrim reaches the innermost chamber (Garbhagraha), his/her eyes slowly become accustomed to the darkness and his/her state of mind befitting worship and is no longer plagued by worldly thoughts. During this journey, one passes through many doorways, colonnaded halls, and corridors, which are decorated with sacred carvings. These sacred symbols have a profound impact on the mind of the devotee; they simulate the mystery that envelops the universe and the divine spirit that illumines the universe (Deva 1995). Reaching the holy sanctum, the worshipper enters a place for individual self-realization and personal relation with the divine."
If this prepared us to arrive at the state of mind conducive for prayer and possible meditation too, the latter brings us to unknown frontiers alien to what we see here with our eyes, we are told. When the Light comes within, the chakras are activated in one by the divine hand. Having worked on it through efforts placed on the practices given by the Siddhas themselves there is little one can do further but to immerse in the bliss and at times the pain and agony that comes with it too. The chakras on opening up further to the brilliance of the Light that descends within receive the full splendor of the Light that enhances the inherent fire within and beauty unfolds. Energy flows from beyond to complement the inherent energies within. The topmost chakra then is in constant touch with the Prapanjam. All the senses are heightened. One feels an action or word done or said to another within him. He begins to relate to another's feelings of joy and pain. This extends to all other creations too eventually. He is one with all around him. He is indeed then a saint in all manner.