[Radiance-general] Re: rsensor file format

[Axel Jacobs]

Greg,

> Radiation as we use it normally is not a volumetric quantity.  It can
> be area-based, but since we report things as a proportion of area
> (e.g., watts/meter^2), this factors out again.  I'm not really sure
> where you're confused, since there are so many things that are
> confusing about lighting units.  I spent months in the beginning
> trying to get my head around them.

By 'volume' I mean the solid of revolution described by the intensity 
values. However, I've just read up on this in Walsh: "Photometry", 1958:

"It might at first be thought that the total luminous flux given by a 
source could be found from the area of the polar curve, or the volume of 
its solid of revolution about the 0-180 deg axis. But a moment's 
consideration will show that this is not the case."

This is where I was coming from. After a lot longer than just one 
moment's consideration, I stand corrected.

Let theta be the altitude (zenith, nadir) angle, and phi be the azimuth 
angle. I is the intensity.

The total flux, assuming rotational symmetry of the 3d curve around the 
nadir-zenith axis (I(theta) is not a function of phi), is

integral(zero, 2pi) integral(zero, pi) I(theta) sin(theta) d theta d phi,

which is

2pi integral I(theta) sin(theta) d theta,

in other words, there is a simple linear relation between flux F and 
I(theta):

F is proportional to I(theta).

So much to light emitters (IES data), and receivers are identical but 
the other way 'round. Simple, really...

q.e.d.

Other than to myself, I hope I didn't cause too much confusion.

Cheers

Axel