I would like to discuss an article found in the March 2008 issue of Advanced Aquarist, Coral Coloration and Incident Light: A Photographic Essay. This article was referenced in another post, although I can't remember who posted it.
Some of the information found in this article is making me rethink how I choose bulbs for my MH fixtures. In the past the number one criteria in choosing a bulb has been it's PAR value, while color temperature came in second. I tried to maximize the amount of PAR that I could acheive from the bulb, without choosing a bulb that was to "yellow". As a result I tended to migrate towards 10K bulbs, while avoiding 20K bulbs as their was to much loss of par when compared to those with a lower kelvin rating.
The assumption underlying this choice was that the more PAR, the more photons available for photosynthesis and as a result the best growth. After reading this article, I am not so sure anymore.
quoting from Schlacher, 2007...
Based upon the above snippet, the 20K bulb had the highest growth rate of all those tested. While presumably the 20K bulb had the lowest PAR rating. (The article did not give information regarding the type of bulb used nor the ballast used for the test, but these assumptions are made based upon Sanjay Joshi's testing)
The article raises a concern about the above test data, pointing out that the bulbs where all placed at the same height above the test subjects. Since the available PAR is somewhat a function of the height of the bulb over the test subject, this would mean that the corals under 10K would have received far greater overall PAR than the corals under 20K, but that the corals under the 20K would have received far greater exposure within the blue spectrum.
If you take a look at the test results as depicted within the photographs in the artice, consistently with the previous test it would appear that in most cases that the corals grown under the 20K bulbs grew faster than the other two test subjects grown under 10K and a T5 array. Not to mention that the corals photographed under 20K bulbs generally had more color.
This leads me to the question, is PAR just PAR or is some PAR better than others? Should I be using higher K bulbs for faster growth. I have always wanted to use higher K bulbs for perceived coloration, but dreaded reduced growth.
Some of the information found in this article is making me rethink how I choose bulbs for my MH fixtures. In the past the number one criteria in choosing a bulb has been it's PAR value, while color temperature came in second. I tried to maximize the amount of PAR that I could acheive from the bulb, without choosing a bulb that was to "yellow". As a result I tended to migrate towards 10K bulbs, while avoiding 20K bulbs as their was to much loss of par when compared to those with a lower kelvin rating.
The assumption underlying this choice was that the more PAR, the more photons available for photosynthesis and as a result the best growth. After reading this article, I am not so sure anymore.
quoting from Schlacher, 2007...
Based upon the above snippet, the 20K bulb had the highest growth rate of all those tested. While presumably the 20K bulb had the lowest PAR rating. (The article did not give information regarding the type of bulb used nor the ballast used for the test, but these assumptions are made based upon Sanjay Joshi's testing)
The article raises a concern about the above test data, pointing out that the bulbs where all placed at the same height above the test subjects. Since the available PAR is somewhat a function of the height of the bulb over the test subject, this would mean that the corals under 10K would have received far greater overall PAR than the corals under 20K, but that the corals under the 20K would have received far greater exposure within the blue spectrum.
If you take a look at the test results as depicted within the photographs in the artice, consistently with the previous test it would appear that in most cases that the corals grown under the 20K bulbs grew faster than the other two test subjects grown under 10K and a T5 array. Not to mention that the corals photographed under 20K bulbs generally had more color.
This leads me to the question, is PAR just PAR or is some PAR better than others? Should I be using higher K bulbs for faster growth. I have always wanted to use higher K bulbs for perceived coloration, but dreaded reduced growth.
