1. Aristotle, On The Soul , Book II
2. R. L. Oldershaw, “Democritus-scientific wizard of the 5th century BC,” Speculations in Science and Technology, Vol. 21, pp. 37–44, 1988
3. Plato, Timaeus
4. K. Seyrafi, Light, The Mystery of Universe. Electro-Optical Research Com-pany Los Angeles, CA, 1986
5. R. Loudon, The Quantum Theory of Light , 3rd Ed., Oxford University Press, Oxford, 2000