Photobiomodulation therapy for osteoarthritis: Mechanisms of action

Table 3 Irradiation

Parameters	SI units	Additional observations
Operating mode	-	Physicians may select a continuous or pulsed wave, for example
Pulse on duration	Seconds (sec)	It is important to equally distribute time intervals between pulse on and pulse off cycles
Pulse off duration	Seconds (sec)
Irradiance at aperture	Milliwatts per centimeter squared (mW/cm2)	Irradiance can be significantly affected by the angular aperture of the light guide. For instance, irradiance measured with an aperture is greater than that without an aperture. Physicians should always keep this in mind
Aperture diameter	Centimeters (cm)	Values may vary significantly across different manufacturers and specific devices are better suited for different application objectives
Beam divergence	Radians or degrees (rad/deg)	Beam divergence may be an important variable depending on the nature and localization of the target tissue
Beam shape	-	The beams may be circular or elliptical, for instance
Laser beam polarization	-	The electric field vibration can be simple, with only one direction along the beam path (linear polarization) or it can be complex
Beam profile	-	Depending on the scenario (clinical or laboratory study), a specific profile may be indicated, such as Gaussian or Top Hat
Peak radiant power	Milliwatts (mW)	This variable must be carefully adjusted according to the target sample being irradiated
Average radiant power	Milliwatts (mW)
Center wavelength (CW). And Spectral bandwidth (FWHM – range of wavelengths)	Nanometers (nm)	Practitioners must carefully select a suitable device with the appropriate wavelength and bandwidth specifications for the intended objectives. The FWHM (Full Width at Half Maximum) filter is important because outside the ideal bandwidth range light can be significantly attenuated
Frequency	Hertz (Hz)	The operator should always be aware of the frequency being applied to the area
Energy per pulse	Joules (J)	This parameter must be adequately regulated depending on the different points to be irradiated. Different tissues may require more or less energy per pulse. In clinical scenarios, the corporal density of each patient may vary significantly. In three-dimensional tissue cultures there are fewer layers of materials impeding light penetration and less scattering

SI Units: International System of Units.