Specific intensity is a measure of the amount of radiation or energy emitted by an object in a particular direction. It is expressed in units of energy per time per area per solid angle. Flux, on the other hand, is a measure of the total amount of radiation or energy emitted by an object, regardless of direction. It is expressed in units of energy per time per area. In simpler terms, specific intensity takes into account the direction of the emitted radiation, while flux does not.
Imagine you are standing next to a light bulb. The specific intensity would be different depending on whether you are facing the light bulb directly or looking at it from the side. This is because the amount of radiation you receive from the light bulb is dependent on the direction you are facing. However, the flux would be the same regardless of your position, as it is a measure of the total amount of radiation emitted by the light bulb.
Specific intensity and flux are related by the solid angle. The solid angle is a measure of the size of the cone of radiation emitted by an object. As the size of the solid angle increases, the specific intensity decreases, but the flux remains the same. This is because the same amount of radiation is spread over a larger area.
It is important to distinguish between specific intensity and flux because they are used to describe different aspects of radiation emission. Specific intensity is useful for studying the properties of a particular object, such as its temperature or composition, while flux is more useful for understanding the overall amount of radiation received by an observer or a target.
Specific intensity is measured using a radiometer or a spectrometer, which can detect and measure different wavelengths of radiation. It is then calculated by dividing the measured flux by the solid angle, which gives the specific intensity in units of energy per time per area per solid angle. The specific intensity can also be calculated from the temperature and properties of the emitting object using mathematical equations.