If you have looked into light therapy, you will have seen numbers such as 650 nm, 810 nm and 1070 nm. They are wavelengths, and for light aimed at the brain they matter a great deal. Here is what they mean, without the jargon.
Wavelength is colour, and depth
A nanometre (nm) is a billionth of a metre, and a light’s wavelength determines its colour. Visible red light sits at around 620–700 nm. Beyond about 700 nm the light is near-infrared, which is invisible to the eye.
Body tissue has what scientists call an “optical window”, a range running roughly from red into the near-infrared. In that range, blood and water absorb relatively little light, so light can travel further before it is used up. Within that window, longer wavelengths generally scatter less, which is why near-infrared reaches deeper than red light.
The same target, different reach
Red and near-infrared light are thought to act on the same molecule in the cell: cytochrome c oxidase, an enzyme in the mitochondria (see what the research says). Each wavelength is absorbed to a different degree, but the bigger practical difference is where the light ends up.
- Around 650 nm (red): absorbed and scattered close to the surface. Well suited to skin, but relatively little reaches the brain through the scalp and skull.
- Around 810 nm (near-infrared): the most widely studied wavelength in brain photobiomodulation research, with good penetration through tissue.
- Around 1064–1070 nm (longer near-infrared): scatters less again, which is why it is proposed to reach further into brain tissue. The 2013 study of attention and mood in healthy adults by Barrett and Gonzalez-Lima used 1064 nm.
What the 1070 nm research looks like
Much of the most interesting 1070 nm research comes from laboratory studies. In 2021, researchers reported in Light: Science & Applications that 1070 nm light pulsed at 10 Hz reduced amyloid build-up and improved memory in a mouse model of Alzheimer’s disease, apparently by changing the behaviour of the brain’s immune cells, the microglia.
Two cautions apply. A mouse skull is far thinner than a human one, and findings in animals often do not carry over to people. Studies in humans using 1070 nm specifically are still limited. We would rather tell you that plainly than overstate it.
Depth isn’t the whole story
Reaching the brain is necessary, but it isn’t enough on its own. What happens also depends on:
- Dose: how much light energy is delivered, and for how long. The ELATED-3 depression trial showed that too low a dose may do nothing.
- Pulsing: whether the light is continuous or pulsed, and at what frequency.
- Coverage: which regions of the head the light reaches.
- Consistency: photobiomodulation is a course, not a one-off.
Sources
- Tao L et al. (2021). Microglia modulation with 1070-nm light attenuates Aβ burden and cognitive impairment in Alzheimer’s disease mouse model. Light: Science & Applications, 10, 179. View source
- Barrett DW, Gonzalez-Lima F (2013). Transcranial infrared laser stimulation produces beneficial cognitive and emotional effects in humans. Neuroscience, 230, 13–23. View source
- Iosifescu DV et al. (2022). Very low-level transcranial photobiomodulation for major depressive disorder: the ELATED-3 trial. Journal of Clinical Psychiatry, 83(5). View source
- Nairuz T, Lee JH (2024). Photobiomodulation therapy on brain. Cells, 13(11), 966. View source
This article is general information, not medical advice. It doesn’t replace the guidance of your own doctor. If you have sudden or severe symptoms, contact your GP, NHS 111 or A&E.
