Irradiance refers to the amount of radiant flux incident on a surface per unit area. It is a measure of the power of electromagnetic radiation per unit area.

Heat flux density represents the rate of heat energy transfer through a surface per unit area. It is a measure of the amount of heat energy passing through a given area in a specific amount of time.

Common examples of related units of measurements include watts per square meter for irradiance, and watts per square meter for heat flux density.

• Irradiance is important in solar energy applications to determine energy generation.
• Heat flux density is crucial in thermal management to understand heat transfer rates.