Irradiance is a measure of the amount of electromagnetic radiation that is emitted, transmitted or reflected by an object in all directions. It refers to the power of light radiated from a surface per unit area and is usually measured in watts per square meter (W/m²). In other words, it describes how much energy is being sent outwards from a source such as the sun, a lamp or any other heat-producing object. The amount of irradiance depends on factors like temperature, distance, and angle of incidence. It can be used to calculate the amount of solar radiation that reaches the Earth's surface, which in turn helps determine how much energy is available for various natural processes such as photosynthesis or human activities such as generating electricity through photovoltaic panels.