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"Ideal" kelvin temp for plants? Phooey!

> From: PSE <pse1 at ix_netcom.com>
> Subject: Degrees Kelvin for plants
>    I have 240 watts of 4' flourescents (Vitalite) which I am told are
> 5000 / 5500 degrees K on a 6' 125 gal plant tank.  I understand this is
> the 'correct' color temperature for optimum plant growth. 

As far as any evidence (both actual in my tanks at home, plus anecdotal
from others on this list) goes, it may not matter what you use for your
plants.  $1 Cool-white fluorescents with their lousy CRI and big green
spike, or $20 vitalites, carefully balanced at 5500K with 95 CRI.  I've
used lights with their color ranging from 2700K through 6500 K and
assorted CRI's, and have gotten good growth from all. What seems to mostly
matter for the plants is the AMOUNT of light you use.

However, the color may very well matter to the observer (i.e. YOU).  It
certainly does to me.  I don't like watching a tank lit with cool-whites.
I much prefer a balance of 6500K as lit by Sylvania F032-765's, which are
cheap but effective simulations of daylight.  If I were using F40's, I'd
go for the GE "Sunshine" bulb (aka Chroma-50) available at Home Depot for
around $5.

> Is 7100 degrees K as good for plants as 5000 / 5500 deg. K.  Does it
> matter?  I have searched the archives and can find no specific answer to
> this question.

So, yes.  They are.

> From: Victor Eng <engfam at axionet_com>
> Subject: [Q] Recycling MH Bulbs from a Reef Aquarium?
> I was just wondering if anyone has used the MH bulbs or PC fluorescent
> bulbs (5500K - 6500K) from Reef Aquarium setups (generally changed every
> 12-18 months) on planted tank?  The reason I'm asking is because, it seems
> a shame to throw away a bulb that still works.  The Reefer's change them at
> this interval because they shift from the blue & green spectrum (which is
> what is favoured by corals) back towards the orange & red.

Same answer here.  Yes, so long as you have enough wattage to grow your
plants, and (as an infamous mattress store says around these parts)
"you're not picky about color".

Incidentally, "Power Compact" bulbs of the 28, 36 and 55 watt variety are
supposed to be similar to T8's, so (this is a speculation) they may have
similar lumen retention charactaristics, i.e. 3 or more times that of
Normal Output fluorescents. i.e. they may not need to be thrown out quite
so soon... I wonder how many reefkeepers have actually bothered to do a
spectral analysis of their 12-month-old bulbs rather than follow old
wives' tales and speculations about bulb life... yeah, I know, probably
about the same as the number of plant people who've done it. :)

    - Erik

Erik D. Olson
erik at thekrib.com (fails? try eriko at wrq.com)