Light and photobiomodulation

Wavelengths, doses and mechanisms behind red, blue, green and infrared light.

Terms (20)

Photobiomodulation (PBM)Photobiomodulation (PBM) is the use of red or near infrared light, at intensities too low to heat or damage tissue, to produce a change in how cells behave. It is the agreed scientific name for what used to be called low-level laser or light (LLLT), and it depends on wavelength, intensity and total dose.
ChromotherapyChromotherapy is the practice of bathing a person in coloured light to influence mood or wellbeing. In our material the word refers only to the ambient status lighting in the Red Light sauna, and we make no health claim for it.
Wavelength (nm)Wavelength is the distance between one peak of a light wave and the next, measured in nanometres (nm). It determines the colour of visible light, how deeply light penetrates tissue, and which molecules in the body can absorb it. For any light-based device it is the single most important specification.
Nanometre (nm)A nanometre (nm) is one billionth of a metre — a thousandth of a micrometre, or a millionth of a millimetre. It is the standard unit for light wavelengths. A micron, used for far infrared specifications, is a micrometre: 12 microns is 12,000 nm.
PhotoreceptorA photoreceptor is a cell or molecule whose function is to absorb light and convert it into a biological signal. In the eye these are the rods, cones and light-sensitive ganglion cells. In photobiomodulation the word is also used loosely for molecules inside ordinary cells that absorb light, more properly called photoacceptors.
ChromophoreA chromophore is the part of a molecule that absorbs light at particular wavelengths — the reason a substance has a colour. In the body the main chromophores are haemoglobin, melanin, water and cytochrome c oxidase, and which ones absorb a given wavelength decides how deeply that light penetrates.
Cytochrome c oxidase (CCO)Cytochrome c oxidase (CCO), also called complex IV, is the last enzyme in the mitochondrial respiratory chain. It transfers electrons to oxygen to make water, a step that drives ATP production. It also absorbs red and near infrared light, which is why it is the proposed target of photobiomodulation.
Nitric oxide (NO) dissociationNitric oxide (NO) dissociation is a proposed mechanism: that red or near infrared light knocks nitric oxide off cytochrome c oxidase, where it had been competing with oxygen and slowing respiration. Removing it would let the enzyme resume normal activity and raise ATP output.
Mitochondrial Stimulation"Mitochondrial stimulation" is an everyday phrase for the proposed effect of red and near infrared light on the mitochondrion: light absorbed by cytochrome c oxidase, nitric oxide displaced, and ATP output raised.
Collagen SynthesisCollagen synthesis is the process by which cells, mainly fibroblasts in skin, build collagen — the fibrous protein that gives skin, tendon and bone their structure and tensile strength. It requires vitamin C and slows with age and ultraviolet exposure.
Low-level laser/light therapy (LLLT)LLLT is the older name for photobiomodulation: light at intensities too low to heat tissue, applied to produce a biological effect. The name has been formally superseded because "low-level" was never defined and the effect is not limited to lasers.
IrradianceIrradiance is how much light power lands on a given area of skin, measured in milliwatts per square centimetre (mW/cm²). It falls off sharply with distance from the emitter, and together with time it determines the dose.
FluenceFluence is the total light energy delivered per unit area, measured in joules per square centimetre (J/cm²). It equals irradiance multiplied by exposure time. In photobiomodulation it is the closest thing to a dose, and more is not automatically better.
Dose-response relationshipA dose-response relationship describes how the size of an effect changes as the dose changes. In photobiomodulation the relationship is biphasic rather than straightforward: a low dose stimulates, a higher dose does less, and too much can abolish or reverse the effect.
Red light (630–660 nm)Red light in the 630–660 nanometre band is the visible part of photobiomodulation. It penetrates a few millimetres into skin and is absorbed by cytochrome c oxidase. It is the band the Red Light sauna takes its name from.
Blue light (therapeutic)Therapeutic blue light is visible light of roughly 400–500 nanometres. It is absorbed close to the skin surface. The Red Light sauna's range starts in the blue, at 460 nm.
Green light (therapeutic)Therapeutic green light is visible light of roughly 500–570 nanometres. Like blue, it is absorbed close to the skin surface, which is why it is used for surface-level skin concerns.
Near infrared 850 nmNear infrared at 850 nanometres is invisible light just beyond red. It penetrates further than visible light — several millimetres, depending on tissue and skin tone — and reaches deeper than red light.
LED arrayAn LED array is a set of light-emitting diodes mounted together to cover an area. In photobiomodulation, arrays have largely replaced lasers because they are cheaper, safer and cover more skin. What reaches the skin depends on how the array is built as well as on the number of LEDs.
Eye safety and lightEye safety with any light-emitting device is decided by measurement — wavelength, irradiance at the eye, exposure time and geometry — not by appearance. Our answer is design: the user's head sits outside the sauna, away from the direct light, and the lights switch off when the doors open.