Radiance

Abbreviated "L," Radiance sensors are easy to inspect because they do not typically have a diffuser.  In our systems, filter-photodetectors are positioned at the bottom of individual Gershun-style tubes.  An endplate restricts the field-of-view to the desired solid angle (PRR-2800 photo at right).  

Different colored filters select the regions of interest in the spectrum (plot below ).   Narrowband ("monochromatic") sensors are equipped with filters that restrict the spectral response to a narrow region, typically 10 nm FWHM.  An example of a broadband radiance detector is the Natural Fluorescence detector (abbreviated LuChl) patented by Biospherical Instruments.  To collect as many fluoresced photons as possible, an LuChl detector approximates the emission spectrum of chlorophyll.