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Old April 25, 2018   #66
cwavec
Tomatovillian™
 
Join Date: May 2016
Location: PA - 5b
Posts: 73
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No question the spectra are different and, yes, I have had good luck with
fluorescents as well.

But bear in mind a couple of points:

1) The 6500K designation is almost meaningless unless you look at the overall
power spectrum. When you do that, you will find that the spectra (at least
considering only fluorescents) are almost the same no matter the Kelvin
rating. There is nothing inside that tube at a temperature that high or even
at 2200K. The Kelvin temperature rating on all these products (LEDs too)
is basically a mathematical/ perceptual trick to make you think the emitted
light is more "white", "red", "blue", "warm", "cool", "daylight" or whatever, etc.

2) You need to look at the actual spectrum power distribution and compare
that with the efficiency spectrum for photosynthesis. This information is
documented and publicly available. If not doing that, you might as well
stick with almost any fluorescent tube, whatever the Kelvin temperature.
Plants don't care anything about the hype associated with any of these
designations.

3) In using LEDs, the Daylight 6500K designation is probably even more
useless and using a fixture that someone dreamed up using red and blue
LEDs is just a handwave in the wind. If you have one and it works for you,
stick with it but understand that you don't understand why it works and
neither does anyone else.

4) The reference I made to LED lights is not to any of the aforementioned
items but specifically to a product developed by Cree explicitly for
horticultural use. They document their technology to an extent that if you
have the stomach for it, you can actually determine what is happening in
the relationship between lights and plants. That is the route I would take
if I were going to build anything new.

That said, please note that a substantial portion of my comment had to do
with poor quality manufacture (shoplights) and/or future lack of availability
(fluorescent tubes). You cannot buy a new shop/garage fluorescent fixture
anymore that is worth having. Everything I have seen in the last 7 or 8
years is either crap or too expensive. Fluorescent tubes will be gone in just
a few years. You will barely be able to get any and even then only at a
price associated only with rarity more than quality.
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