While humans do not possess specialized light-emitting organs like fireflies or deep-sea creatures, every person constantly emits an extremely faint glow. This phenomenon is known scientifically as Ultraweak Photon Emission (UPE), or biophoton emission. The light is a measurable byproduct of basic life processes and is a universal characteristic of all living cells. It is so weak that it remains completely invisible to the unaided human eye, serving as an indicator of ongoing biochemical activity within the body.
The Scientific Reality of Human Light Emission
UPE is a continuous stream of photons in the spectral range of approximately 200 to 800 nanometers. Scientific studies show that this ultraweak glow is not uniform across the body and follows a distinct daily fluctuation. The light intensity tends to peak in the late afternoon and decreases to its lowest level during the night and early morning hours. This diurnal rhythm suggests a link between the emission and the body’s metabolic rate and circadian cycles. Researchers who have successfully imaged the human glow found that the face, particularly the forehead and cheeks, emits the highest photon count. This localized intensity is likely related to the higher concentration of metabolic activity in the skin tissue of these areas.
The Underlying Chemical Mechanism
The source of UPE is a byproduct of cellular metabolism, specifically oxidative stress, rather than a deliberate function. The light-generating chemical reaction is a form of chemiluminescence, occurring primarily within the mitochondria, the cell’s powerhouses. Mitochondria are the main site of oxidative phosphorylation, a process that creates reactive oxygen species (ROS), often referred to as free radicals.
These unstable free radicals oxidize biomolecules, such as lipids and proteins, creating unstable, high-energy intermediates. A common intermediate is a triplet excited carbonyl, formed during the decomposition of lipid peroxides. This excited state is temporary. To regain stability, the excited molecules must drop back down to their lower energy, or ground, state, releasing the excess energy in the form of a photon, which is the light detected as UPE. The intensity of this emitted light can increase significantly when cells are subjected to external stressors, such as ultraviolet radiation, which increases the production of reactive oxygen species.
Why the Glow is Invisible
The primary reason humans cannot perceive this glow is the vast difference between the light’s intensity and the sensitivity of the human visual system. The total number of photons emitted from a square centimeter of human skin is typically only around 10 to 100 photons per second. In contrast, the absolute threshold of the dark-adapted human eye is roughly 1,000 to 100,000 times brighter than this faint emission.
The light is detectable only through the use of highly specialized equipment, such as extremely sensitive, cooled Charge-Coupled Device (CCD) cameras or Electron-Multiplying CCD (EMCCD) sensors. These devices must be cryogenically cooled to reduce their internal electronic noise, allowing them to capture and amplify the few photons being emitted. Furthermore, imaging must take place in a completely light-tight, pitch-black environment, eliminating all external light sources that would otherwise overwhelm the ultraweak signal.
The wavelengths of UPE fall predominantly in the visible to near-infrared spectrum, with researchers detecting emissions ranging from blue-green to red light. Even though the wavelengths are within the visible range, the magnitude of the light is simply too small to trigger a response in the eye’s photoreceptor cells. The human body is indeed bioluminescent, but its glow remains revealed only by advanced scientific instruments.