[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


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 -----
Coral-List at coral.aoml.noaa.gov
[Coral-List] PAR intensity of different kelvin globes

I recently purchased two 400watt metal halide lights and two what I 
were 14000 kelvin globes to conduct some coral bleaching experiments on 
subtropical hard corals.  After setting up the experiment I was not able 
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 
lights the two globe which were first purchased were nearly twice the 
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


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 -----
coral-list at coral.aoml.noaa.gov
[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 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
carin.jantzen at zmt-bremen.de
Zentrum für Marine Tropenökologie
Center for Tropical Marine Ecology
28359 Bremen


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----- Message from Melissa Keyes <mekvinga at yahoo.com> on Fri, 11 Aug 2006 
05:47:01 -0700 (PDT) -----
Coral-List at coral.aoml.noaa.gov
[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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