Yoga Sutras of Patanjali translated by Yogi Kalinath - Chapter 3, Verse 40
Pada 3, Sutra 40
Through mastery of Samaana, radiance
Samaana is the life-air that is responsible for digesting food and distributing the nutrition throughout the body. It therefore stimulates the gastric fire (Agni). The Yogi can obtain control of Samaana by one-pointed concentration on Manipura Chakra. The proper distribution and functioning of Samaana will result in radiant health and vitality.
Furthermore, with the control of the Fire element, one will be able to emit light from one’s body as fire not only produces heat but also light.
Tapas, intense Spiritual Practice and Discipline, will also kindle the Inner-Fire and produce radiance of the body and mind.