[Radiance-general] the disk of the sun

[Zack Rogers]

Hi Mike, I think John's equation may be an equivalent equation - but here
is how I have gone about it using these two equations:

E = L * w * cos(theta)

where w is the solid angle of the sun and theta is the incidence angle on
the illuminance plane; 0 for direct normal illuminance.

Then the solid angle can be determined using this:

w = 2 * pi * (1 - cos (half angle) )

This uses the half angle of the solar disc cone, so roughly .25 degrees.

Cheers,
Zack

On Tue, Mar 6, 2012 at 3:41 PM, John Mardaljevic <jm at dmu.ac.uk> wrote:

> Hi Mike,
>
> See page (number) 60 in chapter 3 here for a description how to derive the
> luminance of the sun from direct normal illuminance:
>
> http://www.iesd.dmu.ac.uk/~jm/doku.php?id=resources:thesis
>
> Includes a little discussion re: the inconsistency of applying a
> measurement taken with an acceptance angle of, say, 6 degrees to a source -
> the sun - that has an angle 0.5 degrees.  Note that the discussion is
> couched in terms of predicting illuminance.
>
> Best
> John Mardaljevic
>
> Reader in Daylight Modelling
> Institute of Energy and Sustainable Development
> De Montfort University, The Gateway, Leicester, LE1 9BH, UK
> Tel: +44 (0) 116 257 7972
>
> jm at dmu.ac.uk
> http://www.iesd.dmu.ac.uk/~jm
> http://dmu.academia.edu/JohnMardaljevic
>
>
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-- 
Zack Rogers, P.E., LEED AP BD+C
Daylighting Innovations, LLC
211 North Public Road, Suite 220
Lafayette, CO 80026
(303)946-2310
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