Re: Chroma 50 vs Vitalight

[busko at stsci_edu (Ivo Busko)]

Ryan Mills <millsman7 at yahoo_com> wrote:

> Chroma 50s may grow plants, but I do believe there is
> a difference in the appearence of the light they
> produce.  Vitalights put out ok looking illumination,
> but Chroma 50s put out a funny yellowish green that I
> can't stand.  Are they really that similar?  Aren't
> Vitalights 500k higher?

According to my normalized spectral plots, their spectra is roughly
similar but there are small differences that might account for the
yellower tint of the C50. Here are some figures: a 40 Watt Vitalite 
puts out 0.16 Watt/nanometer at wavelengths around 500 nanometer; a
40 Watt C50 puts out less, about 0.13 Watt/nanometer. At wavelengths
around 600 nm both put out about the same flux, 0.14 Watt/nm. The
Vitalite is overall closer to the solar spectrum than the C50, that
is, it is "wither", if we adopt the solar spectrum as our "white light"
standard. Thus its color temperature should be closer to the Sun's,
about 5770 K (outside Earth's atmosphere). These differences IMHO are 
very likely irrelevant from the standpoint of growing plants, unless one 
wants to delve into issues related to seasonal response of plants to
light, where small spectral differences seem to play a role. 

-Ivo Busko
 Baltimore, MD

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