In LLT, energy density is influenced by tissue depth and which other factor?

• A. The device used
• B. Patient age
• C. Time since injury
• D. Ambient temperature

Answer: (A)

Energy density in low-level laser therapy is about how much energy is delivered per unit area to the tissue. Tissue depth matters because energy is attenuated as it travels through tissue, but the amount of energy arriving at the tissue surface—and thus the density at which it is delivered—depends primarily on the device settings. The device determines the wavelength, power output, exposure time, and the spot size, all of which set the energy per unit area (J/cm^2). Different devices can deliver very different energy densities even with the same protocol, so the device used is the key factor controlling energy density beyond how deeply the energy must penetrate.

Patient age, time since injury, and ambient temperature don’t directly establish the energy per area delivered to tissue. They may influence tissue response or optics indirectly, but they don’t set the energy density the device delivers.