[Coral-List] PAR intensity of different kelvin globes

D. Wade Lehmann dwlehman at ncsu.edu
Sun Aug 13 10:01:46 EDT 2006

Dr Sanjay Joshi has actually done performance reviews of most major brands
of bulbs and ballasts in use in the aquarium industry.  You can search and
compare differing spectra on his website:

delbeek at waquarium.org wrote:
> Steve Dalton <sdalton at nmsc.edu.au> said:
>> 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
> Steven: Kelvin ratings on commercial lamps sold in the Aquarium industry
> are
> more often than not more abuot marketing hype than fact. The lamps that
> are
> bluer can either be made so by reducing the chemicals that produce longer
> wavelengths and thus letting the blue that is there to be expressed more,
> this
> would then result in a lower PAR value, or the lamps can be made bluer by
> adjusting the chemical balance to produce more blue while the other
> wavelengths remain about the same ... your results seem to suggest the
> former
> situation. Measurement with a spectraphotometer is really the only way to
> know
> for sure what is going on. Measurements done to date have shown
> significant
> differences in some cases between the provided Kelvin rating and what the
> results from the spectrophotometer show for some lamp brands.
> Be aware also that there can be significant differences between lamps of
> the
> same Kelvin rating, and as the lamps age there will be further changes,
> usually
> the blue drops significantly compared to the rest of the spectrum since
> the
> chemicals that produce blue are less stable. Metal halide lamps are, by
> their
> nature, unstable so it is difficult to get ones that maintain spectrum and
> are
> identical when it comes to spectrum.
> If you are not concerned about the amount of blue, then the Iwasaki 6500 K
> lamps are good and produce the most PAR for your dollar/pound. I don't
> have
> access to my home computer at the moment, but if you do a search for
> Sanjay
> Joshi, you will find his website where he has examined a LARGE number of
> metal halide lamps for spectrum and PAR output and you should spend some
> time there to learn more about PAR vs. Kelvin as how these relate to
> aquarium
> metal halides.
> Aloha!
> --
> J. Charles Delbeek
> Aquarium Biologist III
> Waikiki Aquarium
> 2777 Kalakaua Ave.
> Honolulu, HI, 96815
> (808)923-9741
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> Coral-List at coral.aoml.noaa.gov
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