Photobiomodulation in Parkinson's disease: A randomized controlled trial

What the authors concluded

When 8J/cm2 of energy are applied to the head, approximately 2–3% of the near-infrared photons reach the brain cortex at depths of 1cm from the skin or scalp surface, and 0.2–0.3% are estimated to reach depths of 2cm (and thus to reach the white matter). Accordingly, transcranial application of [8?] J/cm2 is estimated to deliver 0.09375 J/cm2 (1.9%) and 0.009375J/cm2 (0.19%) to the brain cortex

Devices that emit this wavelength

Matched on wavelength within 15nm, since LED bins vary by roughly that much and a tighter match would be false precision. Where we have an irradiance figure, the session length is the time needed to reach this study's dose of 8 J/cm² at that intensity.

Matching a wavelength is not the same as reproducing a trial. Session times assume the device's published irradiance is accurate at the distance it was measured, which on brand-claim figures is often optimistic. Where a device publishes both a peak and an average we use the average, and where it publishes a falloff curve we use the lowest figure, so these times run long rather than short. Clinical protocols also control for spot size, contact and skin type in ways a home device cannot.