>Psychtoolbox>PsychRadiometric

cornealIrradiance_PowerPerArea = RadianceAndDistanceAreaToCornIrradiance(radiance_PowerPerSrArea,stimulusDistance,stimulusArea)

Convert the radiance of a stimulus to corneal irradiance, given that we know the distance to the stimulus and the area
of the stimulus. Light power can be in your favorite units (Watts, quanta/sec) as can distance (m, cm, mm). Area
needs to be in units that are the square of your distance units, both for the radiance passed and the stimulus area
passed. So, if radiance is in Watts/[cm2-sr] then distance needs to be in cm and irradiance will be in Watts/cm2.

This conversion, I believe, is correct for the case where the eye is viewing the surface along its
surface normal, if we are thinking about a surface of fixed area. For off axis viewing there will be
a correction for the Lambertian dropoff in light with cos(theta). This differs from computing retinal
irradiance from radiance, where the area of the surface seen by a fixed retinal area increases exactly
so as to compensate for that dropoff.

See also: RadianceAndDegrees2ToCornIrradiance, CornIrradianceAndDegrees2ToRadiance

2/20/13 dhb Wrote it.