The flux density is proportional to the squares of the amplitudes of the component waves. Radiance is closely related to the concept of brightness as associated with luminous bodies. Thus, the Sun, a source, irradiates the Earth's atmosphere and surface. Most wave trains are polychromatic, meaning that they consist of numerous sinusoidal components waves of different frequencies. Any complex wave can be broken into its components by Fourier Analysis which extracts a series of simple harmonic sinusoidal waves each with a characteristic frequency, amplitude, and phase.
EM radiation can be incoherent or coherent .
The above, rather abstract, sets of ideas and terminology is important to the theorist. We include this synopsis mainly to familiarize you with these radiometric quantities in the event you encounter them in other reading. One multiplies the first part of the number by the power of ten in the second part of the number to get its value. Considering the second part of the number, values are assigned to the number 10 n where n can be any positive or negative whole integer . Here the rule is that there is always one less zero than the power number, as located between the decimal point and 1.