I found a website that gave me some information on flourescent lamps. I have copied some of the info below:
Fluorescent Phosphors The color of fluorescent lamps is created by mineral phosphors in powder form which coat the inside of the lamp tube. The chemical make-up of these phosphors determines the lamps CRI, its Color Temperature, and how much light the lamp produces. There are four types of phosphor coatings:
Traditional halophosphors Are inexpensive coatings which usually provide the entire spectrum of light. But, there is a trade-off between Color Rendering and Lumen output. Poor color rendering lamps such as "warm white" and "cool white" have high Lumen output. Good color rendering lamps such as "warm white deluxe" and "cool white deluxe" have low Lumen output.
Prime color or Tri-phosphors Are very expensive coatings with good color rendering and high lumen output. Lamps of this type are produced under the trademark, Ultralume.
Double-coat lamps Have a coat of halo-phosphor and a coat of tri-phosphor. Double-coat lamps which have a thick tri-phosphor coat are fairly expensive but have very good color rendering properties. They are known by the trademarks SPX, Designer 800 series, etc.. Double-coat lamps with a thin tri-phosphor coat are much less expensive, but still have full light output and reasonably good color rendering. These lamps are known by the trademarks SP, SPEC, Designer, and others.
Rare Earth Phosphors Have a thin and thick coat of rare earth phosphors and are just becoming available. The CRI for these lamps will be 70, 80, and 90 and in a variety of Color Temperatures.
Whew, that's more than I wanted to know
but at least it convinces me that all "flourescent" lamps are not equal.
The bulb I'm using doesn't have any info about it's temperature and their website had a range, just like you said Michael. So, I guess the best way is experimentation and maybe try that Verilux bulb.
Joan
P.S. This is where I found the above info:
http://www.lightcalc.com/glossary.html