Re: Aquatic Plants Digest V2 #531

In a message dated 97-02-20 07:21:32 EST, you write:

<< Color temp - after reading and some personal correspondence it seems that
 4100k bulbs may be better for plant growth, while the 5000k and 6100k bulbs
 would be better for color rendition.  Any suggestions on mixing bulbs?
   My knee jerk response is to start with 2/3 4100k bulbs and 1/3 6100k bulbs
 get a strong amount of light farther down in the red and a few high
 bulbs for sheer appearance to he human eye.  Does:
 or does the temp of the color not average out that way?

According To GE's Lighting Application Bulletin  two flourescent lamps that
are somewhat difference in appearance can have the same color temperature,
 which explains why there are so many different "5000K" fluorescent lamps on
the market.  in general your 4100K lamps have a redder appearance and produce
more long wavelength light.  6100K sources are bluer.  I'm guessing that
plant lights and cool whites would give you a similar mix of spectra.  For
viewing you need to look at CRI (color rendering index) instead of color
temperature.  Lamps with color rendering indices  of 85 (on a scale of 100)
or higher will generally give a pleasing, natural appearance to a tank.
 Personal preference plays an important role here also....I use Ultralume 50
(Philips) lamps for viewing, and these look more "natural" to me than their
colortone 75 lamp which has a CRI of 95.  

To answer your question (or not answer it <G>),  for plant health, look at
the spectrum of each lamp to make sure the right wavelengths for
photosynthesis, etc are there.  You can order these from the
manufacturers...many include them in advertisements.  For viewing, go with
whatever looks good and has a reasonably high CRI.  Advertising has made
choosing lights way more complicated than it needs to be.

Pete Mohan