What does fluence describe in laser terminology?

• A. Wavelength of light
• B. Rate of energy delivered to area
• C. Power of the laser per unit area
• D. Duration of the emission

Answer: (B)

Fluence describes how much energy from the laser actually reaches and is delivered to a specific area. It is the energy delivered per unit area, usually expressed in joules per square centimeter. This means fluence is about the total energy that crosses the spot on the tissue, not how fast that energy is arriving.

You can think of it as energy per area, which can be achieved with different combinations of power and pulse duration—as long as the total energy delivered per unit area stays the same. That’s why fluence is different from irradiance (power per unit area), which describes the instantaneous rate of energy delivery.

So the concept tested is understanding that fluence is the energy density delivered to the target area. The option describing the energy delivered to an area aligns with that idea, while wavelengths relate to tissue interaction, duration relates to how long the pulse lasts, and power per unit area is a different measure (irradiance).