A relationship among radiation, matter, and consciousness is proposed. We assume that space and time are fundamental physical quantities and that the space-time is a stage at which the existence manifests itself. We postulate the existence of three fundamental physical entities, i.e., three ways in which existence (energy) manifests itself: radiation, matter and consciousness. By exploring the connections among these entities and the concept of energy, we propose the existence of a fundamental constant of nature related to consciousness phenomena. A possible test to the proposed relationship radiation-matter-consciousness would be to perform a spectral analysis of the photons emitted by a human being, by aiming to detect characteristic photons (consciousness photons) from the conversion... Radiation ↔ Consciousness. Implications of this hypothesis are presented with possible applications in human health and a correlate of consciousness.