Which parameter change decreases the energy density delivered to the skin?

• A. Increasing energy (J/cm2)
• B. Increasing repetition rate (Hz)
• C. Increasing wavelength (nm)
• D. Decreasing energy (J/cm2)

Answer: (D)

Energy density, or fluence, is the amount of energy delivered per unit area of skin (measured in J/cm^2). To decrease how much energy the skin receives, you reduce the energy per pulse, i.e., lower the fluence. The repetition rate changes how many pulses hit per second (speed and potential cumulative heating) but does not by itself lower the energy each pulse delivers. The wavelength affects how the light interacts with tissue (what it targets and how deep it penetrates) rather than the dose per unit area. So lowering the energy per pulse directly reduces the energy density delivered.