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Re: fluorescent tubes
I am trying to decide on which new tubes to buy. I need two 30W for my 160L
(yes, a bit low I know). And I am quite confused. I live in Denmark (Europe
:-) so I can only choose lamps that are available here.
I kind of have decided to go for full spectrum tubes as opposed to some of
the plant tubes. Both Tropica (in their book) and Diane Walstad (in her
book) recommends cool white tubes like Philips TL'D/940 and Osram
Lumilux/22-940. Both have CRI > 90, color temp. of 3800K, and a lumen output
of approx. 1600.
I have used Philips 950s and Osram 950s and I like them both. I prefer the
Philips 950s as they are a little bit brighter.
The situation is somewhat the same for Osram, but they have the
Lumilux/72-965. It has a CRI > 90 and a color temp. of approx. 6500K. It has
a color distribution of "natural sun light". They call the distribution
"biolux" but does not otherwise describe it. How does that sound? does
anybody know this tube?
I have never used these lamps but judging from the spectrum at ( I hope this
I think they would be very good lamps for growing plants and they should be
quite pleasing to look at.
It has a lumen output approx. like the TL'D/90.
Osram also has the Lumilux/21-840 plus eco. It is a cool white, but only has
a CRI of 80-89. I do not know the color distribution. The interesting part
is that it has a lumen output of 2350 compared to the around 1600 of the
other tubes, so it apparently is somewhat brighter. What do you think? This
tube should also be available in higher color temps.
800 series lamps are triphosphor lamps and are always brighter than 900
series lamps. I would not be fooled by that though. 800 series phosphors are
just designed to give you the most lumens possible for the amount of energy
consumed while still giving an above average CRI. They do this by
concentrating the output of the lamp in the areas that are best percieved by
the human eye. This does not mean however that low lumen lamps do not
produce as much plant usable energy as high lumen lamps. 900 series lamps
cannot be designed to produce a lot of lumens and high CRIs. To produce very
good color rendering it is necessary for the lamp to have a full and
continuous spectrum similar to sunlight or a black body radiator. This means
that a lot of light energy is produced in areas of the spectrum that are not
well percieved by the human eye so consequently the lumen rating will be
More general: Should I only look for CRI > 90? Which color temp. should I go
for? Should I use two different tubes? I have been doing a little reading on
the list and on the web, but most information is about US tubes. I know that
CRI, color temp. and lumen output is not really enough information, but
realistically it is all I can get.
The human eye can just barely percieve the difference between a CRI of 90
and a CRI of 95. Even a diiference of 10 points is not very noticable. I
personally can't tell the difference between a lamp with a CRI of 98 and one
with a CRI of 90. So, really high CRIs are not that important visually.
Visually, I would not want something below 80 but anything above that is
OK. OTOH, CRIs of 90 and above mean you have a lamp that has a
continuous and full spectrum and I definately can see a small but
going from a CRI of 80 to a CRI of 90. Currently I mix 950 lamps with 850
lamps and I am quite happy with the results.
The plants could care less about color temperature but it is important to
people. It is a matter of personal taste though. Personally I like anywhere
between 4000K and 6500K. A lot of people say they don't like 4000K lamps but
that probably has more to do with the fact that cool white lamps are 4000K
lamps and many cool white lamps have very poor color rendering. 940 lamps
look very good to my eye but 740 lamps (CRI in the 70s and 4000K) look
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