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Re: compact fluorescent 16.5" biax

> Date: Tue, 26 Mar 2002 11:25:43 -0500
> From: "Kinney, Travis" <kinney at pdtarchs_com>
> Subject: compact fluorescent 16.5" biax
> Hello all,
> I have a (2) bulb 16.5" biax light fixture that I have taken apart and built
> into a custom hood. I'm looking at buying the lamps and don't know what
> Kelvin rating I should look for. Can you guys help? My local electrical guy
> has 3500K and 4100K. 

Either will work well for the plants, but may look a bit "warm" to your eye.
They are close to morning or afternoon sunlight in color. 5000K is more like
mid-day sun, and 6500K is similar to northern skylight illumination (favored
by many artists).

> I was told I should get one Actinic. What K-rating do
> the Actinic bulbs have? 

Don't. They are often 10,000K and too blue for fresh water. Needed for some
reef tanks, they can be mixed with 4000K to get more "white" illumination,
sometimes. Most of their energy seems to lie outside the active growth
spectrum of many plants, unfortunately.

> Am I ok with either of these two lamps that are
> stock or would you recommend I special order? I have a 29-gallon freshwater
> tank with yeast co2 generator and freshwater plants. 

I'd try the stock 4000 lamps and see how they look to you. The two
objectives in illuminating a planted tank are to supply the photosynthetic
energy needed by the plants and to please the viewer's eye. Those are a bit
incompatible, so compromise where you like. If it looks too yellowish,
replace one by ordering a 6500K lamp.

> CRI, Lumens, Kelvin
> ratings, blah blah blah. Beats me! help!

These were all developed for designing store window display illumination, so
take with a grain of salt when applying to aquaria. :-)

CRI is the "Color Rendition Index" on a scale of 0-100, with 100 being the
purest possible white. Look for at least 80. 85 or above will usually look
great. Anything 70 or below will tend to have a definite off-color tint of
some kind.

Lumens mean little to plants. They are based on human vision, which has a
huge sensitivity peak right in the green region that plants need least (they
reflect most of it, if you have noticed). Lumens measure how bright it will
look to you, but sometimes (as in Cool White) the result is very weak red
and blue that the plants can use better. I tend to look for lower
lumens/Watt if I want good plant action.

Kelvin ratings are an attempt to get human visual equivalents to blackbody
radiation colors. Dull red at a few thousand degrees to searing blue-white
at the top. Your brain corrects well for a lot of variation, here, depending
on other surrounding illumination. Stick in the 3000-6500 area for best
looks, IMHO.

This is a highly subjective area, so do be sensitive to what looks good to
you and still grows plants at an acceptable rate. That's my $0.02.


Wright Huntley -- 650 843-1240 -- 866 Clara Dr. Palo Alto CA 94303 

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