Fluence is measured in which unit?

• A. J/cm2
• B. W/m2
• C. Lumens
• D. Pascals

Answer: (A)

Fluence is the amount of energy delivered to a given area. Since energy is measured in joules and the area in this context is often square centimeters, fluence is expressed as joules per square centimeter (J/cm^2). This unit directly reflects how much energy hits each square centimeter of tissue.

Understanding the other options helps: watts per square meter (W/m^2) is irradiance—power per area, i.e., energy per time per area—so it describes instantaneous intensity rather than total energy delivered. Lumens measure luminous flux, a brightness perceptual quantity, not energy to tissue. Pascals measure pressure, unrelated to energy delivery. In laser settings, J/cm^2 is the standard way to quantify fluence.