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How deep does the near infrared light therapy penetrate on the body?Updated 2 months ago

The NASA Study

--p.63, paragraph 3, “. The depth of near-infrared light penetration into human tissue has been measured...Spectra taken from the wrist flexor muscles in the forearm and muscles in the calf of the leg demonstrate that most of the photons at wavelengths of 630-800 nm travel approximately 23 cm through the skin surface (light input) and muscle, exiting at Ihe photon detector.”

It’s counterintuitive if you don’t take into consideration the concept of the optical window of biological tissue. In general, you are correct that “shorter wavelengths typically penetrate lesser depths than longer wavelengths unless you significantly increase the power”. But, due to the main chromophores in the human body, hemoglobin and water, wavelengths on either side of the 600-1200nm optical window are strongly absorbed.

To understand the optical window of biological tissue, refer to Hamblin’s Mechanisms of Low Level Light Therapy.

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