What is the unit for irradiance typically expressed as?

The unit for irradiance is typically expressed as watts per square meter. Irradiance refers to the power of electromagnetic radiation (like light) received per unit area. Specifically, it quantifies how much energy is hitting a surface over a specific time period, hence the use of watts, which measure power (the rate of energy transfer), over an area measured in square meters. This reflects the actual intensity of the radiation at a given point, factoring in both the angle of incidence and the distance from the source.

The other units listed relate to different physical quantities. Joules per second also indicates power, but it is not specifically tied to area, so it doesn't represent irradiance directly. Decibels measure relative sound levels and are not applicable to radiation. Newtons measure force, which is not directly related to energy or power density in the context of irradiance. Thus, watts per square meter aptly describes the concept of irradiance in the context of physics.