One of Einstein's great insights was that matter and energy are different forms of the same thing. Matter can be turned into energy, and energy into matter. Light is the interface or border between them.

As Tenzin Wangyal Rinpoche states: “The realised Dzogchen practitioner, ..., releases the energy of the elements that compose the physical body at the time of death."

More specifically, the rainbow body is constituted by the Five Pure Lights. When the view of Dzogchen and the integrity of the mindstream which links the Trikaya or the three bodies, is realised prior to the death-Bardo (Skt. antarabhava), the bodymind of the Nirmanakaya (Tib. sprul sku) Dzogchenpa enters samādhi (Tib. ting nge ‘dzin) and commences Phowa or the ‘transferral of consciousness’ into the constituent Five Pure Lights of the Sambhogakaya (Tib. longs sku) to the Dharmakaya, sometimes leaving the non-living faecal elements of the bodymind such as hair and nails.