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Potassium and CF Lighting
>Date: Fri, 12 Nov 1999 11:21:34 -0800
>From: "Dixon, Steven T. (Exchange)" <stdixon at ben_bechtel.com>
>Subject: Potassium and CF Lighting
>
>While I'm at it let me offer up an observation I've been meaning to post for
>a while, and ask a question about CF lighting.
>
>
>Am I right in recalling that PAR ratings would give us a rating which would
>better correlate with plants general ability to use light than lumens?
You need to know the spectrum. Lumens correlate with human eye. Basically,
it's a source energy spectrum mulplied by photopic curve (=standard eye
sensivity curve).
PAR is a just number of photons. Photoosynthesis is a quantum process, i.e.
all photons produce equal effect regardless of their energy. Quantum yield
(=is the moles of carbon fixed per mole of photons absorbed) curve is
practically constant in 400-700 nm range (check, fro example, Taiz, Zeiger
Plant Physiology, 1991). As one can see, equal amount of energy of "red"
light produces more PAR photons then same amount of energy of "blue" light.
Unfortunately, uniforme quantum yeild deosn't say anything about overall
ability plant to use light. It only says that if photon get absorbed by
plant it's used with 100% efficiency. But not every photon get absorbed.
Thus, you need to know chloroplast absorption spectrum and how well it
corellates to lamp spectrum. Otherwise, both lumens and PAR are senseless.
Green laser is the most efficent light source. It produce almost 700 lm/W
(1 W = 683 Lm at 555 nm). It produces certaing amount of PAR photons.
However, plants have poor absorptions in green region (that's why we see
plants green). So using a green laser with certain amount of lumen and PAR
gives completely different result than using different power lamp but same
amount of lumens or PAR.
I'd say that the best unit of measure would be something similar to lumens
with using average plant absorption curve instead of eye curve. I never saw
such units, but this is used, for example, for estimation of efficiency of
UV lamp. Lamp spectrum is multiplied by "bacterial" responce.
Next problem. Above will give you corellation with the plant
photosynthesis. But, different part of spectrum produce different effect in
plants - different growth, different vegetaion period, different
productivity (most of studies were conducted with "useful" plants - tomato,
cuccmber, not anubias or crypts. If one can get something from crypts, then
they will be object of research). For example, productivity of tomato
(fruit yiled) is maximal then most energy is in red part of spectrum
PAR % Average daily
400 - 500 nm 500 - 600 nm 600 - 700 nm fruit yields (g/m^3)
60 20 20 100 +/-7
20 40 40 141 +/-8
10 15 75 185 +/-12
(from Proceedings of International Lighting in Controlled Environments
Workshop)
if you look into maximal plants growth size, then you need different
spectrum and so on.
Therefore, you can't judge source only by its lumen/par/watt value.
>
>A few weeks ago Michael Rubin sent me a copy of a note from Erik Olson
>which, if I paraphrase correctly, essentially stated that CF lights are not
>in fact more efficient, that they do not put out more light per watt than
>normal fluorescent bulbs. I do not recall if Erik was referring to lumen or
>PAR output. One of Erik's points was that the technology of the two types
>of bulbs was more or less the same--however it is that these bulbs actually
>work.
>
>Just to make a stupid observation of my own, all seem to agree that the new
>T-8 bulbs are more efficient, which I take to mean that T-8 bulbs put out
>more light per watt (again, I'm not sure if we mean lumens or PAR when this
>is said) than the old T-12 bulbs. So perhaps simply saying that all of
>these bulbs use the same technology doesn't really answer the efficiency
>question.
>
>Does anyone have a definitive answer to this question? Do CF bulbs put out
>more light per watt (lumen or PAR) than regular fluorescent bulbs; than T-8
>bulbs? Do we have data on this point?
>
>Thanks for you views, and apologies for my use of the bandwidth today.
>
>Regards, Steve Dixon San Francisco
>
Check www.philipslighting.com, www.sylvania.com, ge - probably -
www.gelighting.com
They have all catalogs containing all lumen output, so you can calculate by
yourself.
To compare apples to apples you need to note (when you compare lamps of the
same power)
1) lamps with different CCT (corellated color temperature) have different
lumen output. Cool white lamp has the most efficiency
2) In general, lamp wirh high CRI (color rendering index) value has less
lumen output. To get higher CRI lamp spectrum must be "wider" and this
results lower efficiency
3) lamp using ballast with higher ballast factor produce more lumens.
Modern electronic ballasts have ballast factor of 1.0-1.2. ALso,
high-frequency operation increase performance, too.
4) higher power lamps have better efficiency (less "shipping and handling"
losses). For example, 1 40W lamp deliver more light then 2 20W lamps.
Here are some data from Sylvania catalog
Compact Fl. lamp (Dulux-L), 40W, T5, CCT=4100K, CRI=82, length=22.6",
Initial lumens=3150
Similar lamp - 55W - 4800Lm
Pentron High output T-5 39W, 36" 4100K, CRI=82, 3500 Lm
Octron 700 series lamp 40W, T-8, 60" length, CCT=4100K, CRI=75, 3550 Lm,
Octron 800 series lamp 40W, T-8, 60" length, CCT=4100K, CRI=82, 3775 Lm,
Standard rapid start lamp - 40W, 48", 4100K, 3200 Lm
Gro-Lux 40W, 48" - 1200 Lm
if you check european catalog at Philips, Osram-Sylvania sites, you will be
moire impressed by quality of their lamps. In US energy costs nothing
compared to Europe, so nobody cares about light quality and efficiency.
As you can see, T-8 is more efficient. T-5 has same efficiency as T8. T12 -
sucks. Compact fluorescent has less efficiency then T5/T8.....but, don't
forget that they compact. Both tubes block each other. I don't have a
software with me now to estimate light loss, but I can do it tomorrow. I
think bended T-5/T-8 would yeild same efficiency as compact fluorescent
Mike,
who design wierd optics around weird lamps