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Re: Aquatic Plants Digest V2 #811

> Date: Thu, 3 Jul 1997 10:39:58 -0500 (CDT)
> From: mengerin at cs_utexas.edu
> Subject: Re: new light from Energy Savers
>  
> Ok, George, perhaps you can explain.  Coralife is touting their
> 10,000K bulb as being daylight.  All of the comments I can find about
> it indicate that it is a very bright daylight sort of bulb.  However,
> I have a 7100K bulb and it is actinic.  5500K is high noon and 6700K
> is daylight; what gives?

First of all, I hold very little stock in any claims made in an
advertisement, especially one from Coralife.  Just my opinion, of
course.

5500K is generally considered "daylight" and "daylight" film is
balanced for this Kelvin temperature.  "Real" daylight from the sun
varies with latitude and time of day. 

I have not seen their ad and I have no idea what Coralife is trying to
claim in it except perhaps "more is better", i.e., "a 10,000K daylight
bulb is obviously better than a 5500K daylight bulb becuase it has
more Ks".  Remember, scientists and engineers generally don't write
ads...

> I used to be quite confident that going from a 2700K bulb to a 20000K
> bulb was going from yellow to blue.  However, all the verbage written
> about 10-12,000K flourescents and 10-20,000K Metal Halide has me
> doubting this previous assumption of mine.

I can't comment much on this except to note that "Kelvin temperature"
relates to the color given off by an ideal black body of that
temperature. How this relates to natural sunlight filtered by seawater
is beyond me (assuming the higher numbers are targetted at reef tanks).
 
> Can you detail this further relating Kelvin temp to CRI and Lux/Lumens

Sure.  Kelvin temerature has no relation to the Color Rendering Index
or the Lux measure of intensity per area or the Lumens measure of
total light given off except that they are measures of different 
lighting parameters.  

CRI is a measure of how well a light source renders colors compared to
"ideal sunlight" as observed by a human (with "golden eyes", no
doubt).  It's not a very reliable indicator other than numbers closer
to 100 will giver "truer-to-life" colors.  And I suspect that "95" is
not that much different than "90". 

Lumens are a measure of how much light is given off by a source. 

Lux is "lumens per square meter" and is the important measure for
plant tanks.  A bulb giving off 10,000 lumens without a reflector is
far worse than a bulb giving off 3,000 luemns with a perfect reflector
because not many of those 10,000 lumens will be getting to your
plants.
  
> or give a competant, trustworthy source for the info.

Can't do that. Nope.

Adey's "Dynamic Aquaria" has some lighting info in it along with a
color chart of Kelvin temp and spectral charts of various bulbs.

George