[Radiance-general] ies2rad Question - specifying color temperature

[Kera Lagios]

Thanks, Greg! That's what I needed.

Kera

On Mon, Jun 26, 2017 at 4:04 PM, Greg Ward <gregoryjward at gmail.com> wrote:

> Hi Kera,
>
> Lamp color settings in ies2rad are admittedly odd.  What you probably want
> to use is something like:
>
> ies2rad -df -m 0.88 -t default -c my_red my_green my_blue
>
> The red, green and blue values will be multiplied by the 0.88 factor, so I
> guess you want the RGB to normalize to 1.0.  To get these from CIE (x,y)
> chromaticities, you can use rcalc like so:
>
> rcalc -n -e "ix=...;iy=...;" -f xyz_rgb.cal  -e
> "Xi=ix/iy;Yi=1;Zi=(1-ix-iy)/iy" -e "$1=R(Xi,Yi,Zi);$2=G(Xi,Yi,Zi)
> ;$3=B(Xi,Yi,Zi)"
>
> The file "xyz_rgb.cal" is in the standard distribution in src/cal/cal/,
> along with other files like it.  Put your desired (x,y) coordinates in the
> first setting, e.g., -e "ix=0.3153;iy=0.3417".  (On Unix, replace the
> double-quotes with single-quotes above.)
>
> Alternatively, you can edit the "lamp.tab" file or make your own, adding a
> line near the top for your particular source:
>
> /my special LED/ 0.3153 0.3417 0.88
>
> To use this in your command, you need to enclose the argument in quotes,
> so it doesn't think the arguments after the first one are input files, e.g.:
>
> ies2rad -f my_lamps.tab -t "my special LED" ...
>
> Although I caution strongly against it for LED sources, you can also
> compute CIE (x,y) from black body temp using:
>
> rcalc -f blackbody.cal -e T=2700 -e "$1=cct_x(T);$2=cct_y(T)"
>
> The reason I don't recommend this for non-tungsten source is that they
> almost never match a black body spectrum, and their actual chromaticity
> will therefore disagree with their claimed CCT.
>
> Cheers,
> -Greg
>
> *From: *Kera Lagios <keralagios at gmail.com>
>
> *Date: *June 26, 2017 3:02:21 PM PDT
>
>
> Hi Everyone,
>
> When using ies2rad, I am trying to set the color temperature of a various
> LED light sources to a specific color temperature that I want (e.g. 2700k
> or 2400k...).
>
> Background:
> According to the ies2rad man page
> <http://radsite.lbl.gov/radiance/man_html/ies2rad.1.html>, there are a
> few variables that govern this:
> -f *lampdat*
> -t *lamp*
> -c *red grn blu*
> *-*u *lamp*
>
> The man page refers to the lamp.tab look up table which lists items in the
> following format:
> #
> /deluxe warm white/ .440 .403 .85
> /warm white deluxe/ (deluxe warm white)
> /deluxe cool white/ .376 .368 .85
> etc.
>
> If I am looking to set my own x y chromaticity, rather than use whatever
> is in the .ies file header, which option should I use?
>
> When I try to use the "-u" option, which allows you to set the default
> lamp color according to the entry for *lamp* in the lookup table (*lamp.tab),
> *I have tried including the lamp lookup term as both: -u deluxe warm
> white and -u /deluxe warm white/ in the ies2rad command but I get the
> following errors:
> When I run the command with simple variables,  e.g.:
> ies2rad -df -m 0.88 -o CAT CL_TokistarG14Clear_VI-EX_2400K_G14-C.ies
>
> it runs fine.
>
> I'm not sure how to use the -u (or -t, or -f) in conjunction with the
> lamp.tab look up table to specify my own color temperature.  The only way I
> have had success in doing this is to convert a particular color temperature
> (e.g. 2400k) to R, G, B values and then use the -c term followed by the
> converted RGB values.
>
> Thank you!
> Kera
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