The correlation is between the average light wavelength (nm) and the correlated colour temperature (CCI). This is in comparison to so-called black-body radiation, which is emitted by a theoretical perfect radiator. The radiation from such a hot body is a smooth curve which peaks at a wavelength that depends on the temperature. The link shows a few curves for different temperatures. For example, the 6000K radiation curve peaks at 480nm which is in the blue-green area. 6000K black-bodt radiation still appears white (with a slight blue tinge) because it is actually a broad spread of radiation with a peak at 480nm. Notice that the 3000K curve (halogen and incandescent are 2500K-3000K) peaks in the infrared.

OK, back to fluorescents. Most fluorescents don't emit a broad spread of radiation, but it is possible to average out the wavelengths that they do emit to get the average wavelength. The correlated colour temperature is the temperature of black body radiation which would peak at this wavelength. So if the average fluorescent wavelength is 480nm, the tube would have a CCT of 6000K.

Note that this fluorescent tube's spectrum could have a red spike and a blue spike that average to 480nm, or it could come from a big blue-green spike right at 480nm. One tube would appear purple and one would appear blue-green. Neither would appear white. Using three phosphors is the most common modern approach to creating white-ish light. That white-ish light is actually made up of a red spike, a green spike, and a blue spike, and some stuff in between in more expensive tubes. It appears white, but it illuminates certain colours brightly and most colours very dully. It is the classic flat grey cast that comes from a cheap fluorescent. A fluorescent that emitted a broader spread of light wavelength would render more colours better. How close an artificial light is to that ideal broad spread is measured by the colour rendition index (CRI), where 100 is the best.

What this means is that a tube with a higher temperature must emit more light somewhere at the blue end of the spectrum to have an average wavelength that is nearer to blue. Those 6500K bulbs appear white with a bluish tinge, 4100K bulbs appear as a fairly clear white, and 3000K bulbs appear distinctly orange. I knew this picture would come in handy one daya :)

Here is a link that might be useful: Some black body radiation curves

Thanks,

I've yet to read or understand all this. I guess it is like hi-fi equipment. Multiple amps driving their own frequencies result in better resolution and control over the whole spectrum.

I know ROY G BIV.

I have an em spectrum chart I pulled from a book called 'Living In Space'. Is there any way to post this scan in a message in this forum? I do not have a link, nor my own page. I have a scanner and photo software, though.

Bentley, e-mail me to get my e-mail, then e-mail it to me and I'll host it if you'd like.

Mark

Unfortunately, I can't sharpen it enough, and it's got my notes all over it. It is a wavelength-frequency-photon energy chart of the entire em spectrum on one side and a stimulus-receptor-sensation for humans on the other. It has
tv am fm, radar, molecular studies, infrared, visible( ROYGBIV), ultraviolet, atomic studies, X-Rays, radiation therapy, gamma rays, cosmic rays on one chart. From the Radiation chapter in 'Living In Space...'. I believe of all these choices, the author is George Harry Stine.

I thought it could put things into perspective.

After I read the 13 book Asimov series all in a row, I got into the bones, evolution, history of man, universe, space shuttle, space station, living in space thing. I believe of all, the author is George Harry Stine.