LED light like Mercury Vapor and others is "spikey" in color emission spectra.
As opposed to incandescent Tungsten, Arc, Xenon, and the good old Sun more smooth.
fluorescent is somewhere in-between.

I am having trouble mixing LED with other sources for a "natural" transition of tone.
http://www.ledtronics.com/TechNotes/...tes.aspx?id=24

See fig 3.
http://www.olympusmicro.com/primer/l...rcesintro.html