Small reminder that the radiant flux (power) is the time density of energy and the irradiance is the area density of the flux. Given a sensor with area 'A', we can consider the average flux over the area: flux/A. Therefore, the irradiance (E) is given by taking the limit of the area at a single point on the sensor, resulting in W/m^2.

Small reminder that the radiant flux (power) is the time density of energy and the irradiance is the area density of the flux. Given a sensor with area 'A', we can consider the average flux over the area: flux/A. Therefore, the irradiance (E) is given by taking the limit of the area at a single point on the sensor, resulting in W/m^2.