Red light therapy wavelengths explained

A nanometre is one billionth of a metre, and it is how we measure the wavelength of light. Shorter wavelengths appear blue; longer ones appear red and then pass out of visible range into infrared.

Why the number alone is not enough

Wavelength tells you what colour of light a device emits. It says nothing about how much of it reaches your skin. That depends on the output of the LEDs, how many there are, how they are arranged, and how far the array sits from your face.

This is why irradiance — energy delivered per unit area — is the most useful single figure, and the one most frequently missing from product pages.

Comparing two devices fairly

• Compare wavelengths individually, not as a blended description.
• Check whether irradiance is stated, and at what distance it was measured.
• Note the treatment area — a larger array at the same irradiance covers more skin per session.
• Compare the manufacturer's stated session length, since a shorter session at higher intensity is not the same offer as a longer one.

Be wary of precision without provenance

A very specific number with no stated measurement conditions is marketing, not data. If a brand publishes irradiance, it should also say how and where it was measured.

Where confirmed, we publish manufacturer-supplied specifications on the relevant product page. Where a figure has not been confirmed, we leave it out rather than filling it in.