I was creating a light source the other day, from an IES file. Turns out this was to be my first encounter with an IESNA LM-63-95-formatted file, on a directional, linear fixture. Well, the first time, using Radiance that is.
I ran the *non*-directional downlight file thru ies2rad and then checked it in ltview, and it looked like this:
So far so good.
Then I ran the *directional* downlight file thru ies2rad and checked it in ltview, and it looked like this:
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, because the spec is so loosely written. This is why checking the distribution of my converted luminaires is so important to me, prior using them in a calc. I always did it because I don't trust myself, but clearly too much faith in the quality of your input files is also a bad thing.
Anyhoo, I simply reversed the length and width values for the luminous opening parameters in the ies file, and got this:
Now, I have a useable fixture, albeit one with a default plan orientation that is 90 degrees off from the norm. I guess I could "wrap" the whole thing in an xform file so that I could use it in a standard library.
Is there a better way to "correct" a funky IES file for ies2rad? What do you all do when you encounter this?
- Rob G.