Re: Question about the Sylvania light posting

[busko at stsci_edu (Ivo Busko)]

"Ben B." <benrx at naxs_net> wrote:

> I'm a couple days behind on my reading, so sorry this is a little late.
> 
> I have a question about the post below.  I was curious about the Sylvania
> lights and looked at the file.  As I thought I understood it, CRI compared a
> light's quality to Sunlight and a value of 100 most closely represented the
> that of the Sun.  Also, a temperature of 5,500K is considered close to
> natural sunlight.  If you look at the CRI and the temp. of some of the
> lights in the file, there is no correlation.  Some 3500K lights have a
> higher CRI than a 5000K light.  Apparently I have something confused.  Could
> someone fill me in?
> 
> Thanks,
> Ben

CRI and color temp. are not correlated. Quoting from 
http://www.kruschwitz.com/cri.htm:

"CRI is a unit of measure that defines how well colors are rendered by 
different illumination conditions in comparison to a standard (i.e. a 
thermal radiator or daylight)".

Note that sunlight does not enter the definition at all. When measuring 
the CRI of a, say, 3,500K light source, the standard to be used is a 
3,500K thermal source (black body), not a 5,000K source. This is why 
incandescent bulbs always have a CRI of 100 by definition, since they
*are* thermal sources. It doesn't mean that they produce sunlight though.

- Ivo Busko
  Baltimore, MD

  "Buy a fish, Save a tree !"
  Project Piaba: http://www.angelfire.com/pq/piaba/

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