[Radiance-general] IES file fun

[Stefano Callegari]

Il 11Jun 16:08, Rob Guglielmetti scrisse:
> I was creating a light source the other day, from an IES file.  Turns 

First, are you sure the ies data are correct?

[cut]
> 
> http://www.rumblestrip.org/site-img/rad/linear.jpg
> 
> So far so good.

It seems a symmetric fitting.

> 
> Then I ran the *directional* downlight file thru ies2rad and checked it 
> in ltview, and it looked like this:
> 
> http://www.rumblestrip.org/site-img/rad/assym.jpg

This time it seems an asymmetric fitting. What you meen with
*directional*?

> Eureka!  I have defied physics!  It was after looking at this image that 
> I re-checked the ies file, and discovered that it's the LM-63-95 spec. 
> This is a problem, because the spec calls for the 0-180 vertical plane 
> to be oriented parallel to the lamp axis, whereas it's more common to 
> orient it perpendicular.  ies2rad can't even have a check for this, 

It's right, the 0-180 plane normally must be oriented parallel to the
lamp axis. This is a general rule to point right the fitting.

The IES specifies:

[...]
This integer value indicates the type of photometric web used for the
photometric measurements as follows:

  Value Description

    1   Type C photometry
    2   Type B photometry
    3   Type A photometry

Luminaires are photometered by locating the luminaire at the center of
an imaginary sphere and measuring the light intensity (candela) values
at grid points (the "photometric web') on the sphere's surface. The
orientation of the luminaire's axes relative to that of the sphere
determines the photometric type.

Type C photometry is normally used for architectural and roadway
luminaires. The polar axis of the photometric web coincides with the
vertical axis of the luminaire, and the 0-180 degree photometric plane
coincides with the luminaire's major axis (length).

Type B photometry is normally used for adjustable outdoor area and
sports lighting luminaires. The polar axis of the luminaire coincides
with the minor axis (width) of the luminaire, and the 0-180 degree
photometric plane coinicides with the luminaire's vertical axis.

Type A photometry is normally used for automotive headlights and signal
lights. The polar axis of the luminaire coincides with the major axis
(length) of the luminaire, and the 0-180 degree photometric plane
coinicides with the luminaire's vertical axis.
[...]

Normally the major axis in the type C (the most used) coincides whit
the lengt of the lamps. If the lamp is vertical in the fitting, like a
downlight, the luminous flux is normaly simmetric so is not important
which is the 0-180 plane.

If the fitting has an asymmetric reflector, then the direction of the
max flux coincides at 90° (0° 3 o'clock, 90° 12 o'clock)

> because the spec is so loosely written.  This is why checking the 

I have a good text about the IESNA Photometric Data File (about 33K).
If you need it, could I attach it to the ML?

[cut]
> Is there a better way to "correct" a funky IES file for ies2rad? What do 
> you all do when you encounter this?

If the rad is wrong most likely you have a bad IES file. 

Ciao
-- 
Stefano Callegari <tecnico at omniluxlighting.it>
Omnilux Srl
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