Living cells glow. Not metaphorically — they emit ultra-weak particles of light called biophotons. The main source is mitochondria. As they make ATP, some electrons leak, reactive oxygen species form, and excited molecules dump that energy as faint photons. You can’t see it with your eyes. Sensitive cameras can. A 2025 study imaged whole live mice in the dark. The animals produced a ghostly glow. After they died — even when kept at body temperature — the light dropped. Same pattern shows up in leaves and isolated cells. Life has a faint optical signature that fades when metabolism stops. The more interesting claim is that mitochondria don’t just emit this light — they may respond to it. Isolated mitochondria in one dish can change the respiration of mitochondria in a neighbouring dish with no chemical contact. Block the light path and the effect weakens. Cancer-cell mitochondria appear to send a stronger signal. That’s why people are talking about non-chemical, photonic communication inside cells. This is not “we proved cells have a fibre-optic internet.” The photons are extremely sparse, the field has a fringe history, and alternative explanations still exist. But better detectors and cleaner experiments have pulled biophotons out of the “aura” bin and into real mitochondrial biology. If light is even a minor signalling channel, it changes how we think about energy, stress, and how dysfunction spreads from one mitochondrion to another. Worth watching: imaging of the live glow, isolated-mitochondria transfer experiments, and whether specific wavelengths can actually nudge ATP production. The chemistry of the cell is still king. Light may be a quieter language running underneath it.