Basic Photometric Quantities

In spectroscopic applications of light sources it is very useful to define some characteristic quantities of the emitted and absorbed radiation. This allows a proper comparison of different light sources and detectors, and enables one to make an appropriate choice of apparatus for a particular experiment. 

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 or radiant flux O [W] is the radiant 

The above three quantities refer to the total radiation integrated over the whole spectrum. Their spectral versions W (v), 3 (v), and p (v) are called the spectral densities and are defined as the amounts of W, O, or p within the unit frequency interval dv = 1 s around the frequency v. 

Consider a unit surface element dA = l m of a light source (Fig.2.6). The 

An important quantity is the radiant intensity I = / L dA of the source. This represents the flux per unit solid angle from the entire source [W ster ]. The total flux is then 

All samples in this chapter are assumed to consist of multiple scattering and fluorescent planar layers of arbitrary thickness d. One surface of the layer is irradiated monochromatically at A with parallel light ofintensity /o (per unit area perpendicular to the direction of propagation) under the angle ao relative to the normal of the surface 

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