Radiant energy density

I. Symbol for density. (i.e., mass density). 2. Symbol for charge density. 3. Symbol for radiant energy density. 

In their simplest form, radiometers monitor irradiance (in W/cm ) and radiant energy density (in J/cm ) for the bandwidth of the instrument. Profiling radiometers can in addition to that also provide irradiance profiles as a function of time. The results from the monitoring of a process can be effectively used to correlate exposure conditions to the physical properties of the cured product. If needed, they can also become the specifications of exposure in the design of production systems. Usually, radiometers are placed in the same position as the material that is being cured. 

Spectral quantities may also be defined with respect to frequency v, or wavelength 2 see spectral radiant energy density above. 

Consider a gas of molecules with two electronic states, an excited state m and the ground state n (Figure 2.3), in equilibrium with an electromagnetic field of radiant energy density p emanating from a black-body light source such as the Sun. 

This equation can be identified with the spectral radiant energy density, denoted dp/do and expressed in J.m given by the first Planck radiation formula given below, where c = 2nhc is the first radiation constant and c, = hc/k the second radiation constant ... 

The radiant energy W (measured in joules) refers to the total amount of energy emitted by a light source, transferred through a surface, or collected by a detector. The radiant power P = dlT/dt (often called radiant flux [W]) is the radiant energy per second. The radiant energy density p [J/m ] is the radiant energy per unit volume of space. 

---