Quote:
Originally Posted by Rumpelteazer
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In fluorescent tube they had a coding (at least in the Netherlands) that did not only give the kelvins but also the quality of light: 827 is 2700k in quality 8, 840 is a good quality cool white, but 640 is a lower quality 4000k, with a bluish tint to it. You also have the daylight tubes, which are quality 9; 950, 960, etc, but because of the quality of light they give 30% less light than the quality 8 tubes.
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The "standard" for the quality value is the Color Rendering Index (CRI), which in North America is normally listed as a 2-digit number. the CRI represents the percentage accuracy of the light source compared to a Black Body Radiator of the same Kelvin temp. The Euro style quality numbering seems to parallel CRI rounded to a single digit (e.g. Quality 8 ~= CRI 80).
For normal use, a CRI of 80 or greater is fine. For color matching or color photography, a CRI of 90 is considered a minimum.