You may find some research expressed in Joules
Joules is the energy applied but with without
considering the size of the beam.
Quoting Joules alone is considered to be an
inadequate way of expressing dosage as it does not take into account
the size of the beam.
However both methods are on there own are insufficient.
a) Bolton, Young and Dyson (1)
showed that an identical "dosage" from two different power lasers
do not give the the same results in vitro.
(1) Bolton, P., Young S., Dyson M., (1991) Macrophage responsiveness
to Light Therapy with Varying Power and Energy Densities. Laser
Therapy Journal 105-111
b) It is difficult to accurately measure the
spot size of an invisible infrared beam that is only a couple of
mm2. The beam is usually not circular, and the density of the light
across the beam is not uniform (see example of typical LLLT beam
below). I suggest that there is little consistency between manufacturers
/ researchers regarding measurement of beam density (irradiance).
c) I suggest that different treatment dosage
should be given for patients of different build and presenting with
In clinical practice the science gets forgotten
and the "art" is practiced