Monday, October 27, 2008

Neodymium bulbs sacrifice colour rendering index and aren't full-spectrum or like daylight or sunlight

I thought that neodymium glass light bulbs (like GE Reveal or Sylvania Daylight Plus) just tweaked the spectrum a bit. Today I ran across a post which said their spectrum is irregular and they have a pretty low colour rendering index (CRI) of about 70. Since that's just one post on a message board, I did a bit of research. I found the same issue mentioned in other sources such as a PDF on Colour Rendering Index and LEDs and a page talking about the disadvantages of full-spectrum light sources. The latter lists the CRI of a 60W GE Reveal A-lamp as 78. (Note that fluorescents generally have a higher CRI!) Another page claims "Reveal© bulbs produce CRIs in the neighborhood of 92-93" and shows a graph comparing spectra. In the graph you can see the sharp dip in the yellow region. Neigher the spectrum of the neodymium glass bulb or the normal incandescent bulb is at all like sunlight or daylight (for example, there's this graph from an article on light sources). Neither daylight nor sunlight have a sharp dip in yellow, and both have considerably less red than neodymium bulbs.

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