Red Light Therapy - Wavelengths & dose
Can you overdo it? The biphasic dose response
Last reviewed 13 August 2026. How we write this.
Why more light is not automatically better: the biphasic dose response and what it means for reading claims.
One of the more robust ideas in photobiomodulation research is that the relationship between light dose and effect is not a simple straight line. Researchers often describe it as biphasic - meaning the response can differ at low versus high doses rather than simply increasing with more exposure.
What biphasic means
The general observation reported in the literature is that too little light may do little, a moderate amount may produce the effects being studied, and beyond a certain point additional light may add nothing further or may work against the effect. This is frequently summarised by the phrase that more is not better. It is a useful corrective to the intuition that longer sessions or brighter panels must be superior.
Why this matters for reading claims
A biphasic response undercuts a common marketing logic: that a higher-powered device, or a longer session, is inherently more effective. If effect depends on landing within a range rather than maximising exposure, then bigger numbers are not automatically an advantage - and could, in principle, be a disadvantage. The precise shape of this curve is still being characterised and appears to differ between outcomes.
- The dose-response is described as a curve, not a straight upward line.
- Marketing that equates more power or longer time with more benefit is oversimplifying.
- The exact optimal dose for a given outcome is often uncertain and study-specific.
Educational only. This lesson explains a research concept and does not tell you how long to use anything or which dose to choose - that is not something this classroom advises. It is not medical advice; consult a qualified professional where relevant.
Related in this classroom
The studies behind this page
- Mechanisms and mitochondrial redox signaling in photobiomodulation - Photochemistry and Photobiology, 2018
Sources for this classroom
Educational content only. Not medical advice, diagnosis or treatment. Always consult a qualified healthcare professional before changing your health regimen.