LLLT terms and metrics.

Wavelength, in nanometres (nm) is a measurement of the light wave, it is the distance between one point in the wave and the same point in the next wave pattern, in light waves it is measured in nanometres. One nanometre is one billionth of a metre. Wavelength determines the color of the light if it is visible and determines what chromophores will absorb light and higher wavelengths have more energy than shorter ones.

CCO is likely a big factor and so it’s absorption spectrum as a chromophore is important. A chromophore is simply a part of a molecule that absorbs light such as the basis of plant photosynthesis chlorophyll. The absorption factor for water is relatively low within the LLLT spectrum until 900nm where it increases dramatically.

Watt (W) is the unit of power, a measure of energy and time. One watt is the energy consumption rate of one joule per second. A milliwatt (mW) is a thousandth of a watt and is the more common LLLT power metric.

A Joule (J) is a measurement of a unit of energy. It is equal to the energy transferred to an object when a force of one newton acts on that object in the direction of its motion through a distance of one meter. This states dose as a single expression and ignores irradiance.
Power in (W) × time (s) = Energy (Joules) This mixes medicine and dose into a single expression and ignores irradiance. Using Joules as an expression of dose is potentially unreliable as it assumes assumes a reciprocity relationship between irradiance and time. So 100mw for 60 seconds would equal 6 Joules total transferred.

Irradiance time is the length of treatment.

Irradiance, often called Power Density It is power, measured in Milliwatts usually / Area, measured in CM usually. For a 1,000mW light on a 10×10 cm area of skin would be 10mW/cm2

Energy density, (J/cm2) is also called fluence, this is another metric used as a statement of dose and may be problematic as it ignores the metrics of time and probably more importantly irradiance.

Treatment interval takes into account the time between treatments and the total time period that the treatment period takes. It seems to be an important factor and may itself prove to be biphasic when all other parameters are maintained within effective ranges.

Pulse structure is is a description of the parameters of pulsed beams. Pulsed beams are not continuous and their diffrerent frequencies, measured in Hz may make treatments more effective. Frequencies and pulse duration need to be further investigated. The power of a pulsed beam is measured as the average power output taking into account the gaps in the beam. Non pulsed sources are called CW or continuous wave.
(This is generally for higher powered treatments with a wavelength above 900nm)

Coherence is a measure of spectral bandwidth. Coherent light produces laser speckle, which has may play a role in the interaction with cells and sub-cellular organelles. The dimensions of speckle patterns coincide with the dimensions of organelles such as mitochondria.
(Laser specific)

Polarisation. Polarized light may have different effects than otherwise identical non-polarized light (or even 90° rotated polarized light). However, it is known that polarized light is rapidly scrambled in highly scattering media such as tissue. However,protein structures such as collagen the transmission of plane polarized light will depend on orientation. Studies have
demonstrated effects on wound healing and burns with polarized light.