P3D Re: colour temperature levels

[Dylan The Hippy Wabbit <spacey@xxxxxxxxxxxxx>]

Bill Strickley asked:-

>)Does anyone know what the color temperature levels are for warm-white
>and cool-white fluorescent tubes? Can you make any recommendations?
>Thank you.

I'm afraid the concept of a colour temperature doesn't fit comfortably on
fluorescent tubes at all.  They work in a very different manner.

I'm sure we've all seen a hot piece of metal glow yellow, then orange and
red as it cools.  That's where the concept of a colour temperature comes
from, because the colour is largely a characteristic of the temp rather
than the material.  Physicists call it black body radiation, and it's the
principle behind tungsten/halogen bulbs.  Even flashguns shove enough
energy through a small enough volume of gas to briefly heat it until it
glows the same colour as the sun.  BTW, that's why it's not safe to open a
flashgun.  There's a lot of welly in even a small one and you don't want
it to escape through you.

Fluorescent tubes aren't like that.  The atoms in that powdery coating are
excited by ultraviolet radiation.  (Er, I'll gloss over where that comes
from if you don't mind.)  That energy is then re-emitted at a wavelength
which depends on the chemical nature of the coating.  Each type of atom
present can only emit light at a few very well defined wavelengths.  So
while you could produce a lop-sided but continuous rainbow from a tungsten
bulb, a fluorescent jobby would only contain a few discrete colour lines.

The designers have got very good at blending coatings that appear to glow
white, but film reacts differently to light.  I never met one that didn't
look green on film.

Dave



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