# color of the light source

**URL:** <https://discourse.radiance-online.org/t/color-of-the-light-source/3216>\
**Category:** radiance-general\
**Created:** [May 14, 2004, 8:32pm UTC](https://discourse.radiance-online.org/t/color-of-the-light-source/3216 "2004-05-14T20:32:39Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![Bei\_Xiao1](https://discourse.radiance-online.org/letter_avatar_proxy/v4/letter/b/c89c15/32.png) [@Bei\_Xiao1](https://discourse.radiance-online.org/u/Bei_Xiao1)\
**Post date:** [May 14, 2004, 8:32pm UTC](https://discourse.radiance-online.org/t/color-of-the-light-source/3216/1 "2004-05-14T20:32:39Z")

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HI,  
Thank you all very much for the previous replies.  
I have another very rudimentary questions about the rendering. I use  
a point light source in my rendering of the following parameters:  
void light bulb\_light  
0  
0  
3 5000 5000 5000  
Am i suppose to render the scene with white color?  
But this light source illuminate the room with yellowish color. How can I  
get the white illumination? Is there any parameter that I need to set to  
get the correct color of thelight?

Thanks a lot.

Bei

---

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**Author:** ![Greg\_Ward1](https://discourse.radiance-online.org/letter_avatar_proxy/v4/letter/g/3be4f8/32.png) [@Greg\_Ward1](https://discourse.radiance-online.org/u/Greg_Ward1)\
**Post date:** [May 14, 2004, 8:46pm UTC](https://discourse.radiance-online.org/t/color-of-the-light-source/3216/2 "2004-05-14T20:46:35Z")

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Hi Bei,

Colored sources are a complex issue due to white balance. Instead of giving you a long-winded and incomplete reply, I'll refer you to the paper I coauthored on the subject:

&nbsp;&nbsp;[Picture Perfect RGB Rendering Using Spectral Prefiltering and Sharp Color Primaries](http://www.anyhere.com/gward/papers/egwr02/)

Have you been following the related thread on spectral reflectance?

-Greg

> **···**
>
> > From: Bei Xiao \<beixiao@mail.med.upenn.edu\>  
> > Date: May 14, 2004 1:32:39 PM PDT
> > 
> > HI,  
> > Thank you all very much for the previous replies.  
> > I have another very rudimentary questions about the rendering. I use  
> > a point light source in my rendering of the following parameters:  
> > void light bulb\_light  
> > 0  
> > 3 5000 5000 5000  
> > Am i suppose to render the scene with white color?  
> > But this light source illuminate the room with yellowish color. How can I  
> > get the white illumination? Is there any parameter that I need to set to  
> > get the correct color of thelight?
> > 
> > Thanks a lot.
> > 
> > Bei

---

<div class="post-metadata">

**Author:** ![Bei\_Xiao1](https://discourse.radiance-online.org/letter_avatar_proxy/v4/letter/b/c89c15/32.png) [@Bei\_Xiao1](https://discourse.radiance-online.org/u/Bei_Xiao1)\
**Post date:** [May 14, 2004, 10:40pm UTC](https://discourse.radiance-online.org/t/color-of-the-light-source/3216/3 "2004-05-14T22:40:12Z")

</div>

Hi, Greg  
Thank you. I am generating hyperspectral images using Radiance and also  
PsychotoolBox. For right now, I rendered 24 chips of the macbeth  
checker board to test the code of generating right color of hyperspectral  
images. But the color of the objects come out weird because the light has a yellowish  
color. So everything looks yellowish.

&nbsp;&nbsp;I follwed the thread of the specular reflectance. But i am not so clear  
what does the -st (specular thresold mean). Currently, I set the -st as  
0.1. But I found whatever falue I use for specular reflectance, the effect  
of the glossiness is not big.

Thanks,

Bei

> **···**
>
> On Fri, 14 May 2004, Greg Ward wrote:
> 
> > \_Hi Bei,  
> > \_  
> > \_Colored sources are a complex issue due to white balance. Instead of  
> > \_giving you a long-winded and incomplete reply, I'll refer you to the  
> > \_paper I coauthored on the subject:  
> > \_  
> > \_ [Picture Perfect RGB Rendering Using Spectral Prefiltering and Sharp Color Primaries](http://www.anyhere.com/gward/papers/egwr02/)  
> > \_  
> > \_Have you been following the related thread on spectral reflectance?  
> > \_  
> > \_-Greg  
> > \_  
> > \_\> From: Bei Xiao \<beixiao@mail.med.upenn.edu\>  
> > \_\> Date: May 14, 2004 1:32:39 PM PDT  
> > \_\>  
> > \_\> HI,  
> > \_\> Thank you all very much for the previous replies.  
> > \_\> I have another very rudimentary questions about the rendering. I use  
> > \_\> a point light source in my rendering of the following parameters:  
> > \_\> void light bulb\_light  
> > \_\> 0  
> > \_\> 0  
> > \_\> 3 5000 5000 5000  
> > \_\> Am i suppose to render the scene with white color?  
> > \_\> But this light source illuminate the room with yellowish color. How  
> > \_\> can I  
> > \_\> get the white illumination? Is there any parameter that I need to set  
> > \_\> to  
> > \_\> get the correct color of thelight?  
> > \_\>  
> > \_\> Thanks a lot.  
> > \_\>  
> > \_\> Bei  
> > \_