Quantification of the absorption of low-level 904 nm super pulsed laser light as a function of skin colour

Low-level laser therapy is an effective treatment for relief of pain, tissue repair and inflammation and has been extensively used in clinical settings. The effects of laser are dose-dependent and a number of identified factors affect the laser dose received by the patient. To examine the relationship between laser transmission and skin pigmentation, a power meter was used to measure transmission of super pulsed 904 nm low-level laser therapy through the thenar web and cheek pad of participants with skin colour represented by a range of values on the Fitzpatrick scale of skin darkness. The slope of the function of laser transmission against skin darkness value was not significant at the cheek where the confounding effect of cheek pad thickness could not be quantified, however dorso-palmar depth of the thenar web was measured to control for the thickness factor. Laser transmission was found to significantly decrease with increasing skin darkness at the thenar web. Over the range of Fitzpatrick scale values employed, from 2 to 6, there was a 24% decrease in energy transmission at this site. We calculated that for each Fitzpatrick scale point of skin pigmentation after a value of 2, there was a 6% decrease in energy transmission due to absorption by progressively darker skin colours.