function radiance_PowerPerAreaSr = RetIrradianceAndPupilAreaEyeLengthToRadiance(irradiance_PowerPerArea,irradianceS,pupilArea,eyeLength)
% radiance_PowerPerAreaSr = RetIrradianceAndPupilAreaEyeLengthToRadiance(irradiance_PowerPerArea,irradianceS,pupilArea,eyeLength)
%
% Perform the geometric calculations necessary to convert a measurement of retinal
% irradiance to the source radiance that would produce it.
%
% Perform the geometric calculations necessary to convert a measurement of source
% radiance to corresponding retinal irradiance.
%
% Let x be the units of distance (m, cm, mm, um, etc.)
%
% Input irradiance_PowerPerArea is in units of power/x^2-wlinterval.
% Input irradianceS gives the wavelength sampling information.
% Input pupilArea should be in units of x^2.
% Input eyeLength should be the length of the eye in x.
%
% Output radiance_PowerPerAreaSr is in units of power/x^2-sr-wlinterval.
%
% Light power may be expressed in watts or quanta-sec or in your
% favorite units. Indeed, it may also be passed as energy rather
% than power.
%
% This conversion does not take absorption in the eye into account,
% as this is more conveniently foldeded into the spectral absorptance.
%
% See also: PsychRadiometric, RadianceAndPupilAreaEyeLengthToRetIrradiance, PupilAreaFromLum, EyeLength.
%
% 3/6/13 dhb Wrote it.
% Define factor to convert radiance spectrum to retinal irradiance
% and apply this in the opposite direction. See
% RadianceAndPupilAreaEyeLengthToRetIrradiance for the
% conversion logic.
conversionFactor = pupilArea/(eyeLength^2);
radiance_PowerPerAreaSr = irradiance_PowerPerArea/conversionFactor;