[diam,area,trolands] = PupilDiameterFromLum(lum,[source])

Compute pupil diameter and area from photomic luminance.
Diameter is in mm, area in mm^2.
Luminance is in cd/m2.
Also returns photopic trolands.

Source (string):
PokornySmith: (default)
Formula is Eq. 1 from: Pokorny and Smith, “How much light
reaches the retina”, Colour Vision Deficiences XIII (C.
Cavonius, ed.), pp. 491-511.

        Formula is De Groot and Gebhard's from  
        Eq. 2(2.4.5) of Wyszecki and Stiles,  
        2cd edition (page 106).  

Formula is Moon and Spencer’s from
Eq. 1(2.4.5) of Wyszecki and Stiles,
2cd edition (page 106).

a) The calculations of the DeGroot/Gebhard formula do not seem to agree with the
same calculations as expressed in Figure 2(2.4.5) on the same page of W+S. One would
need to go back to the original literature to sort out what is going on.

b) In terms of the different methods, Joel Pokorny (1999, personal communication) says:  
    The average pupil diameter/luminance functions in the literature vary enormously.  
    This can be seen in the figures in   
        Moon, P. and D. E. Spencer (1944). "On the Stiles-Crawford Effect."   
        Journal of the Optical Society of America 34: 319-329.  
        de Groot, S. G. and J. W. Gebhard (1952). "Pupil size as determined   
        by adapting luminance." Journal of the Optical Society of America     
        42: 492-495.  
    For example, the Reeves (1918, "The visibility of radiation." Transactions of the  
    Illuminating Engineering Society 13: 101-109) pupil diameter function is displaced  
    roughly 1.5 log units higher on the luminance axis than Crawford's (1936, "The dependence  
    of pupil size upon external light stimulus under static and variable conditions."  
    Proceedings of the Royal Society B (London) 121(B): 376-395) average data.    
Both Moon and Spenser & [DeGroot](DeGroot) and Gebhard sought functions which were compromises  
    between existing data sets.  LeGrand's function shows good correspondence with  
    the Reeves' data.  These three functions nominally describe pupil behavior for binocular  
    view of large fields.  In vision science we most frequently use fields of limited extent  
    and often use monocular view.  These stimulus manipulations lead to larger pupils than  
    the binocular large field condition.  Thus it made sense to me to use the [LeGrand](LeGrand) function.  
    As is mentioned in "How much light..." pupil size varies for all sorts of reasons and any  
    estimate should be viewed as having a large tolerance.  

4/2/99 dhb Wrote it.
5/8/99 dhb Consolidated different methods.
7/8/03 dhb Accept strings without dashes.
12/4/07 dhb Added dog case, with a place holder number of 8 mm.

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