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E. & O. E.
05/08/2006, 09:28 AM
Hi Sanjay,

color temperature is a really nice topic - but I´m not sure whether i´t is a topic, which is important for our corals: Sure enough corals will grow under "daylight" (about 6000K) up to 15000K. Obviously they are able to live in a wide "color-range" and that´s the reason - I think - why it isn´t important that the lamp has a cct close to the black body locus.

Nevertheless let me say some words to your last article. You wrote: "we should expect the CCT of metal halide lamps sold in the hobby to be close to black body locus, in the vicinity of their specified color temperature." I wonder, why we should expect this! I think it is as you said: "The aquarium lighting industry has used this color temperature interpretation as a way to label their lamps." And we know, that 15000K is "bluer" than 10000K.

Is it really necessary to use a lamp with cct close to black body locus? I don´t think so, because even the sun doesn´t behave like a black body. The Planck-graph for T= 5800 K isn´t the graph you get from the sunlight.
One reason is that in the highest atmosphere of the sun some elements absorb some lines out of the spectrum and they emitt - send out - them at longer wavelengths. For example hydrogen, magnesium, calcium and natrium. This absorption is the reason for the Frauenhofer-lines. (I mentioned them in my thread "light" same weeks ago.) In our atmosphere oxygen absorbs a line. Ozone absorbs in the uv-area, steam and C02 in the infrared-area. So if you show the photon flux density over the wavelenghts you won´t get the distribution of the black body.

Finally the most important thing: Again it was a pleasure to read your "lectures on light"! Your articles remind me of the fact, that our hobby has much to do with physics.

Regards

Erwin Kerkenberg

Sanjay
05/08/2006, 12:54 PM
<a href=showthread.php?s=&postid=7324999#post7324999 target=_blank>Originally posted</a> by E. & O. E.
Hi Sanjay,

color temperature is a really nice topic - but I´m not sure whether i´t is a topic, which is important for our corals: Sure enough corals will grow under "daylight" (about 6000K) up to 15000K. Obviously they are able to live in a wide "color-range" and that´s the reason - I think - why it isn´t important that the lamp has a cct close to the black body locus.


Color temperature is being used to describe bulbs in the hobby, and to distinguish between bulbs being sold. Hence I think it is important that the hobby understand what the terms mean and how they relate to "correct" definations, not the misuse of the terms by the aquarium lighting industry.


Nevertheless let me say some words to your last article. You wrote: "we should expect the CCT of metal halide lamps sold in the hobby to be close to black body locus, in the vicinity of their specified color temperature." I wonder, why we should expect this! I think it is as you said: "The aquarium lighting industry has used this color temperature interpretation as a way to label their lamps." And we know, that 15000K is "bluer" than 10000K.


How do we know that the 15000K aquarium lamp is bluer than the 10000K., without understanding what and where that Color Temperature comes from. ? Secondly, how do we even know if the lamp being sold as 15000K is even close to what is claimed ?
Thirdly, there is enough evidence to show that the aquarium industry rating of the lamps by thier color temperature is very subjective and no where near what is claimed. Hence it is necessasry for us as aquarist to understand the one number that gets thrown around rather arbitrarily and used to sell lamps.



Is it really necessary to use a lamp with cct close to black body locus? I don´t think so, because even the sun doesn´t behave like a black body. The Planck-graph for T= 5800 K isn´t the graph you get from the sunlight.
One reason is that in the highest atmosphere of the sun some elements absorb some lines out of the spectrum and they emitt - send out - them at longer wavelengths. For example hydrogen, magnesium, calcium and natrium. This absorption is the reason for the Frauenhofer-lines. (I mentioned them in my thread "light" same weeks ago.) In our atmosphere oxygen absorbs a line. Ozone absorbs in the uv-area, steam and C02 in the infrared-area. So if you show the photon flux density over the wavelenghts you won´t get the distribution of the black body.


You are right the sun does not behave as a true black body but it comes very close to it. The same is the case for lamps.. hence the correct term used is CCT, which allows the lamp to deveiate from the black body locus, and yet can provide a Color temperature for it. It is not necessary for the corals to have the spectrum that is identical to the black body, they do tolerate a wide range of spectrum as we have seen our aquariums. The corals care more about the spectral distribution of light rather than the CCT. However, if CCT is being used then it should be used to reflect properly the color appearance of the lamp.

This would solve a lot of problems with lighting designations and the proper perception of the light from the lamp. Why is it that there are 14K, 14.5, 18K lamps being sold where it very possible that the 14K can be even more blue than the 18K or 20K. This makes it very difficult for the hobbiest to select lamps. Its not cheap to experiment with lamps, to make up for the industries misuse of well accepted terminology.


Finally the most important thing: Again it was a pleasure to read your "lectures on light"! Your articles remind me of the fact, that our hobby has much to do with physics.

Regards

Erwin Kerkenberg

You are welcome.

sanjay.

E. & O. E.
05/09/2006, 01:13 AM
Hi Sanjay,

thank you for answering so quickly and for opening my eyes for a new problem. I didn´t know "that there are 14K, 14.5, 18K lamps being sold where it very possible that the 14K can be even more blue than the 18K or 20K." And of course you are right in pointing out that "it is necessasry for us as aquarist to understand the one number that gets thrown around rather arbitrarily and used to sell lamps.
Unfortunately I don´t believe, that the bulb manufacturers will soon accept our demand for correctly declared - with regard to the CCT - bulbs. The reason is, that they are obviously not able to do this:
I´ve got four 400 watt lamps over my aquarium. The aquarium is standing in a room with white walls and a white ceiling and the light of the lamps get reflected on the surface of the aquariumwater. So it is very easy to see differences in color temperatures of the bulbs only by looking at the walls. I had to learn, that there are bulb manufacturers who aren´t able to produce four bulbs with identical color temperature. By now I found a merchant, who gives me twelve bulbs and I select four of them with nearly identical color temperature. But this isn´t the end of the problem: Three or four months later color temperature of the four bulbs start to change - and they don´t change the same way. So I learned that it´s better to watch what´s happening in the aquarium than to watch what´s happening with my formerly white walls ...
Obviously it is very difficult to get a constant mixture of elements into the bulbs. This seems to be the reason for the differences in color temperatures of new bulbs. And secondly it seems to be difficult to stop color-change determined by the age of the bulb. These are the reasons why I don´t believe that we´ll ever get bulbs with a correct - and constant ! - CCT. But if the bulb manufactures do efforts and produce such a bulb: so much the better!
Let me say finally some words to the problem why there is a continuous distrubution of wavelenghts in the distribution of the light from a hqi-bulb. I remembered that the double-line of Na is visible only shortly after starting the bulb. As soon as the bulb is getting hot both lines get wider and only one thick line is visible. In physics this phaenomenon is known as the result of the fact that the time, an atom has got to send out the light, is getting shorter if the atom is pushed by other atoms. (A higher temperature means faster atoms and the chance of getting pushed increases.) If an atom has a shorter time to send out light the possible wavelengths are increasing. So aquaristic has much to do with quantum physics :) And now it´s clear, why there is a continuous distribution of wavelenghts.
I hope my remarks are - in spite of my bad English - a bit understandable.

Best wishes

Erwin Kerkenberg