[Coral-List] PAR intensity of different kelvin globes (Andrew Trevor-Jones)
atj777 at attglobal.net
atj777 at attglobal.net
Sat Aug 12 01:39:36 EDT 2006
Steven,
Before answering your specific questions, I feel I need to clarify a few
things. If you already know this information, I'm sorry for repeating it.
PAR is a measure of the amount of light reaching a surface rather than the
output of a lamp. i.e. the number of photons hitting an area over time.
As such the PAR of a lamp is undefined.
PAR also treats all photons equally. Photons of a higher shorter
wavelength (higher frequency) have higher energy levels than longer
wavelength photons. The differences in energy levels is not taken into
consideration with PAR - although a meter may have to deal with it and
normalise the readings.
Metal halide lamps are point light sources and so the further you move
away from the lamp, the greater area over which the light is spread and so
the lower the irradiance. If measuring PAR of a metal halide lamp, you
will get different readings at different distances from the exact same
lamp. You will only be able to compare the PAR from the different lamps if
you are measuring PAR under the exact same conditions - i.e. the exact
same distance from the lamp with the lamp in the same fitting and
reflector. Even with these things being the same, there may be subtle
differences in the readings due to aberrations in the glass of the lamps.
Another thing to consider is the PAR meter being used. Does it measure
all wavelengths equally? The PAR meter I have (from Apogee Instruments)
under reads blue light and over reads red light. If you are using a LiCor
sensor, this may be less of a problem, but it is worthwhile finding out
the spectral sensitivity of the sensor.
Yet another factor to consider is that different brands of lamps will have
different output spectra and light output even if they are the same
wattage and claimed colour temperature. You may even see differences
between lamps of the same brand and same claimed colour temperature. Also,
the claimed colour temperatures of lamps is only very approximate and gas
discharge lamps don't really simulate theoretical black bodies.
Assuming that you are measuring each lamp under the same conditions and
the sensor is not under reading blue light, you should still expect to see
less PAR with lamps of the same wattage but with a higher colour
temperature because there will be proportionally more photons with higher
energy levels. As energy can not be created nor destroyed, the same
amount of input energy (the wattage of the lamp) cannot produce more
energy and so there will be fewer total photons produced by a lamp that
has more blue light.
If the new lamp looked more blue then it would have had a higher
approximate colour temperature. Whether it was 20000K and the originals
were 10000K is not going to be easy to measure. If you could measure the
spectrum of each lamp, you could compare that to the spectra of
theoretical black bodies at various colour temperatures.
I hope this helps.
Andrew Trevor-Jones.
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Today's Topics:
1. PAR intensity of different kelvin globes (Steve Dalton)
2. alkalinity anormaly method (Carin Jantzen)
3. Spawning times for the US Virgin Islands? (Melissa Keyes)
----- Message from Steve Dalton <sdalton at nmsc.edu.au> on Fri, 11 Aug 2006
12:53:19 +1000 -----
To:
Coral-List at coral.aoml.noaa.gov
Subject:
[Coral-List] PAR intensity of different kelvin globes
I recently purchased two 400watt metal halide lights and two what I
assumed
were 14000 kelvin globes to conduct some coral bleaching experiments on
subtropical hard corals. After setting up the experiment I was not able
to
get consistent PAR intensity across all temperature treatment so I had to
purchase another 400 watt light. The problem was that the globe that were
provided with the additional fitting appeared more blue than the original
globes and when I measured the PAR intensity output of the three
individual
lights the two globe which were first purchased were nearly twice the
value
of the more blue light. The supplier indicated that the third globe was a
different brand and so sent another globe that was the same brand as the
first two. This did not solve the problem because the new globe was still
noticeably bluer than the original ones and the PAR output was still
considerably less. Could it be that the original globes were a lower
kelvin value say about 100000K which would explain why they were less blue
than other globes? Or the more blue globes are 200000K and marked
incorrectly. Does anyone know how I can tell what kelvin rating these
globes are and whether PAR intensity decreases with kelvin rating when the
globes have the same watt rating?
If anyone can help me regarding these question I would really appreciate
your comments
Cheers
Steven Dalton
PhD student
University of New England
NMSC Postgraduate Representative
National Marine Science Centre
Bay Drive, Charlesworth Bay
(PO Box J321)
Coffs Harbour, NSW Australia 2450
Ph: 6648 3928
Mob: 0432 946 782
sdalton at nmsc.edu.au
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----- Message from "Carin Jantzen" <carin.jantzen at gmx.net> on Fri, 11 Aug
2006 14:41:17 +0200 -----
To:
coral-list at coral.aoml.noaa.gov
Subject:
[Coral-List] alkalinity anormaly method
Dear collegues,
I am looking for a publication of Smith and Kinsey, 1978 "Calcification
and organic carbon metabolism as indicated by carbon dioxid", p.469-484.
In D.R.Stoddart and R.E.Johannes (eds), coral reefs: Research methods.
Monogr. Oceanogr. Methodol. 5. UNESCO. I know its quite old, but I hope
some of you might have it, and it would be very kind if you can provide me
with a copy? maybe one knows another publication, where the alkalinity
anormaly technique is decribed in all details and can send me a file of
it. This would be very nice!
Thanks a lot,
best regards
Carin
Carin Jantzen
PhD Student
c.jantzen at lrz.uni-muenchen.de
Coral Reef Ecology (CORE) Working Group
GeoBio Center
Ludwig Maximilian University München
Richard Wagnerstr. 10
80333 München
Germany
carin.jantzen at zmt-bremen.de
Zentrum für Marine Tropenökologie
Center for Tropical Marine Ecology
Fahrenheitstr.6
28359 Bremen
Germany
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----- Message from Melissa Keyes <mekvinga at yahoo.com> on Fri, 11 Aug 2006
05:47:01 -0700 (PDT) -----
To:
Coral-List at coral.aoml.noaa.gov
Subject:
[Coral-List] Spawning times for the US Virgin Islands?
Hello, Listers,
If anyone can furnish expected dates and times for this year's coral
spawnings, especially for Acropora palmata and Dendrogyra cylindus, I
would be very grateful.
Thank you in advance,
Melissa Keyes
St Croix, U.S. Virgin Islands, Caribbean
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