Spectral radiance is the radiant energy per time interval, per wavelength interval, per area, and per solid angle that is received by a detector oriented normal to the source of radiation. Spectral radiance is abbreviated L(λ), where λ is the center wavelength of the detector. Submersible radiance sensors are normally oriented to measure the nadir (upwelling) spectral radiance, abbreviated Lu(λ). The calibration unit of spectral radiance used in our radiance sensors is µW.cm-2.nm-1.sr-1 although nE.m-2.s-1 sr-1(where nE is nanoEinstein) is used to measure natural fluorescence (Lu(chl)). Note that the SI unit for spectral radiance is W.m-2.nm-1.sr-1.