Re: Color Temperature -- The ICI (CIE) Chart -- The I See It Rules

["S. Hieber" <shieber at yahoo_com>]

Wright Huntley adde some comments about color temp ratings
and and light spectra and my rules of thumb:

 
>  > Some rules of thumb:
> 
> But lets get them right. OK?
> 
> > 
> > 
> > The apparent color of a complex light beam is made up
> of
> > one or more various different color light beams.
> 
> Sometimes, but not usually. Most light sources are a
> smooth continuum, and 
> don't have spectral peaks (different, separate colors).

Actually all light, with the expection of single wavelength
sources, few of which are in the aquarium lamp secdtion of
the fish store.  Triphosphor bulbs (Like VHOs and PCs
usually do have peaks.  As do doped bulbs like MHs.

> 
> > 
> > Different combinations of colors at different
> intensities
> > will yield the same color temp rating but not the same
> > apparent overall color.
> 
> One can make up any particular apparent color by adding
> different source 
> colors in the right amounts.
> 
> The same is *not true of color temperatures.  They are
> not white and 
> should not be described as having a color temperature
> unless their 
> coordinates lie on (or pretty near) that black line in
> the CIE chart. If 
> they do, they always will look exactly the same.
> 
> The habit has been to allow tube manufacturers to apply a
> guess of color 
> temperature, even when they make a fairly non-white tube.
> That causes the 
> confusion. Plant and Aquarium bulbs of a magenta hue have
> no real color 
> temperature. They are just not white. Period. Likewise,
> green Cool White 
> tubes are fairly far off the white curve. Our brain
> compensates, but a 
> color photo taken under them looks bizarre (if accurate).

Yes, the point is how to treat the color temp ratings of
the bulb manufcturers -- the same color temp can have
different appearence colorwise.

> 
> > 
> > Some overall colors of complex light beams make things
> look
> > natural, others make them look funny-colored.
> 
> Yes. This is complicated by the fact that we have tricky
> ways to 
> compensate, in our brain, for illuminations of different
> color.
> 
> A green shirt looks green at noon and at sunset, even
> though the 
> illumination has gone from bluish white (sun plus sky) to
> rather 
> orangeish. 7000K to 2000K.
> 
> We tend to mentally "force" things to look their right
> color under lots of 
> different lamps. An aquarium looks very different in a
> dark room (where it 
> is the main source of light) and in a brightly lit room
> (where it is not). 

Well, I guess we're going into the realm of the Gestalt
research after all.  :-|


> I think I did! [I spent some years at a University
> researching color 
> displays and human perception thereof. Guess I got
> carried away. ;-)]
> 

And the info isn't lost on us.  Still, I offer the rules of
thumb for folks that don't want to spend time at the
University but just want to make some reasonable choices
about bulbs for planted tanks.

Scott H.

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