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Color Temperature -- The ICI (CIE) Chart
- To: Aquatic Plants Digest <Aquatic-Plants at actwin_com>
- Subject: Color Temperature -- The ICI (CIE) Chart
- From: Wright Huntley <jwwiii at pacbell_net>
- Date: Fri, 14 Feb 2003 16:47:27 -0800
- User-agent: Mozilla/5.0 (Windows; U; Win98; en-US; rv:1.0.2) Gecko/20021120 Netscape/7.01
Lots of strange comments, here, on perceptions of the different color
temperatures of lamps makes me want to say "WHOA!" :-)
First, go to:
and examine the good chart provided at the top of the page.
This is effectively a slice through the entire human vision coordinate
space. [Our ability to see color drops as the light gets too bright or two
dark, so the 3D shape is about like a sweet potato, with points at the
black (dark) and white (too bright) limits. That brightness axis is
perpendicular to the chart, as shown. See the gray scale, 2 pictures down
A dark line is plotted through the color space, running from red through
bluish-white. Color Temperatures fall on this line, or they are not white.
Yes, some tubes are far from white. Nevertheless, the color temperatures
are defined as being on or imperceptably close to the line. Every color
temperature can be given a set of x and y coordinates defining its exact
location on the chart.
A tube that looks magenta or greenish is well off that white curve and
will probably have a very low CRI, as a result. CRI is how much the lamp
makes colors appear to be illuminated by a true white source. That has
little to do with its color temperature. IMHO, manufacturers shouldn't try
to use color temperature on lamps below a CRI of 75 or so. To do so can be
Study that curved black line and note where color temperatures lie along
it. The difference between 5000K and 6500K isn't a whole lot. The old B&W
TV phosphors used to look very blue when we saw them through a window from
outside. That's because the color temperature of those phosphors was about
8600K. Old incadescent lamps (before they tinkered with them so much) were
about 3200K and looked very yellow compared to the "white" of the TV.
I hope this helps some to see what color temperature is all about.
PS. The chart was generated by the International Committee on Illumination
about 60-70 years ago. [The French initials are sometimes still used
despite our better judgement. ;-)] The purpose was to provide standards
and definitions for decorating store windows, displaying meat, etc. They
did the human testing to define Lumens, Lux, and a host of other
"psychophysical" or photometric units, as opposed to the radiometric units
used by physicists and engineers (Watts, Einsteins, etc.).
Wright Huntley -- 209 521-0557 -- 731 Loletta Ave, Modesto CA 95351
"Everything is relative. In most of coastal California,
Ted Kennedy would be politically middle of the road --
and, in San Francisco, right of center."
-- Thos, Sowell JWR 2/14/03