What Is Photobiomodulation? A Plain-Language Guide

Photobiomodulation is the use of specific wavelengths of red and near-infrared light to influence how cells produce and use energy, without heating or damaging the tissue. It is the science behind what most people call red light therapy, and it is the mechanism every reputable eye-light device is built on. Understanding it makes the difference between using these devices sensibly and being sold marketing.

This guide explains photobiomodulation in plain terms: what it is, how it works at the cellular level, which wavelengths matter, why the dose is so important, and how it applies specifically to the eyes. For the device and condition specifics, our research reviews and eye-device buying guide go deeper.

What is photobiomodulation?

Photobiomodulation, often shortened to PBM, is the application of light in the red to near-infrared range to produce a beneficial biological effect in cells, rather than to cut, burn, or heat tissue. That last part is the defining feature: PBM uses light at low enough power that the effect is photochemical, working through how cells absorb light, not thermal.

It was historically called low-level laser therapy or cold laser therapy, and the term photobiomodulation was adopted to capture that the effect is not limited to lasers and can either stimulate or, at the wrong dose, suppress cellular activity. A review of ocular PBM describes it as light in these ranges driving cellular energy processes without the photochemical damage associated with shorter, higher-energy light (Gaspari et al., 2024).

How does photobiomodulation work?

The leading explanation centres on the mitochondria, the structures that produce most of a cell’s energy. Red and near-infrared light is thought to be absorbed by an enzyme in the mitochondria called cytochrome c oxidase, which can boost the cell’s production of ATP, its energy currency, and trigger helpful signalling (de Freitas & Hamblin, 2016).

The practical takeaway is that PBM does not add anything to the body; it nudges cells that are stressed or underperforming toward more normal energy production. This is why it is studied across so many tissues, from skin to muscle to the retina, since mitochondria are everywhere. It is also why the effects are supportive and gradual rather than dramatic and immediate.

What wavelengths are used in photobiomodulation?

PBM uses wavelengths in roughly the 600 to 1000 nanometre range, spanning visible red and invisible near-infrared light. This band is sometimes called the optical or therapeutic window, because light here penetrates tissue better than shorter wavelengths and is absorbed well by the mitochondrial targets.

Within that window, certain wavelengths recur in research. Red light around 660 to 670nm and near-infrared around 810 to 850nm are among the most studied, and for ocular tissue the most examined ranges are 670nm red and 810nm near-infrared (Gaspari et al., 2024). Different wavelengths penetrate to different depths, which is why some devices combine more than one.

Why the dose matters: the biphasic response

The single most important and least understood fact about photobiomodulation is that more is not better. PBM follows a biphasic dose-response curve, meaning a moderate dose produces a benefit while too much light can reduce or cancel that benefit (Huang et al., Dose-Response 2009).

This is why reputable devices specify a fixed session length and why protocols matter more than raw power. A brighter device or a longer session is not automatically more effective and can be counterproductive. The skill in PBM is delivering the right dose to the right tissue, not the most light possible.

What is photobiomodulation used for?

Because mitochondria are universal, PBM has been studied across a wide range of uses, including skin rejuvenation, wound healing, muscle recovery, joint pain, and hair growth. The quality of evidence varies a lot by application, and being studied is not the same as being proven for a given condition.

For the eyes specifically, PBM is researched for dry eye and meibomian gland dysfunction, retinal conditions such as age-related macular degeneration, and the general support of aging retinal cells. The evidence is strongest where there are device-specific trials and weaker where it rests on the general mechanism, which is exactly the distinction our condition reviews draw out.

Photobiomodulation for the eyes

The eye is a natural target for PBM because the retina is one of the most metabolically demanding tissues in the body, packed with mitochondria. That is the rationale behind retinal PBM research, including work in which a single 670nm exposure improved colour-contrast sensitivity in older eyes (Shinhmar et al., 2021).

In practice, ocular PBM ranges from clinic systems with regulatory authorization for specific diseases to at-home wellness masks and glasses. The science is the same; what differs is the dose control, the evidence behind a specific device, and the supervision. Our photobiomodulation for eye health overview maps that landscape.

Is photobiomodulation the same as red light therapy?

For practical purposes, yes. Red light therapy is the consumer term for photobiomodulation using red and near-infrared light. Low-level laser therapy and cold laser therapy are older names for the same idea, originally describing laser-based delivery, while LED-based devices now deliver much of the same wavelength range. The mechanism and the dose principles are identical regardless of the label or whether the source is a laser or an LED.

Frequently asked questions

What does photobiomodulation actually do to cells?

It delivers red or near-infrared light that mitochondria absorb, which can increase ATP energy production and helpful cellular signalling (de Freitas & Hamblin, 2016). It supports normal cellular energy rather than adding anything to the body.

Is photobiomodulation the same as red light therapy?

Yes, in everyday use. Red light therapy is the popular name for photobiomodulation with red and near-infrared light, and low-level laser therapy is an older term for the same mechanism.

What wavelengths does photobiomodulation use?

Generally 600 to 1000nm, covering red and near-infrared light. For the eye, 670nm red and 810nm near-infrared are the most studied ranges (Gaspari et al., 2024).

Is more light or a longer session better?

No. PBM follows a biphasic curve, so a moderate dose helps and an excessive one can cancel the benefit (Huang et al., 2009). Follow the device’s preset dose.

Does photobiomodulation heat the tissue?

No, that is the point. PBM works at low power through a photochemical effect, not by heating, which separates it from thermal light treatments.

Is photobiomodulation safe for the eyes?

Used as intended, ocular PBM has a good safety record, with a review reporting no adverse effects at typical therapeutic doses (Gaspari et al., 2024). See our eye-safety guide for the details and contraindications.

The bottom line

Photobiomodulation is the use of red and near-infrared light to support how cells produce energy, working through the mitochondria rather than by heating tissue, and it is the science underneath red light therapy. The two ideas that matter most are that the effect is gradual and supportive, and that the dose is biphasic, so more is not better. For how this plays out in the eye, read our photobiomodulation for eye health overview and the condition-by-condition research reviews.

This guide is educational and not medical advice. It does not create a doctor-patient relationship. Always talk to a qualified eye-care professional before starting any light-based therapy.