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Old 02-24-2004, 02:43 PM   #1
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Hi Tom,
I didn't want to hijack that thread but I would like to learn more about what you've stated.

Everything I've read about the Kelvin temp of bulbs points to what I stated in that Actinic thread.

If I'm wrong I would like clarification so that I don't state inaccuracies in the future.

Please explain why these are incorrect. I appreciate the time.

1 - It is my understanding that no matter how hot you get a black body it will not produce light as energetic as 420 nm. Therefore, I believe that 420nm does not have a Kelvin temp rating.

2 - Everything I've read has stated that the Kelvin Color scale has a maximum of 20,000K and this is in the blue range.

3 - I've read that 320 - 400nm is in the UV-A range and is invisible to the human eye.
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Old 02-24-2004, 03:06 PM   #2
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Hi BangGuy,

I think there is a bit of misinformation about this but here is a site that has an intereactive tool which makes te relationship between this stuff pretty clear:

http://skyserver.fnal.gov/en/proj/ad.../blackbody.asp

Basically this is a simple scoop. The balck-body approach: This is based on a theoritical object which produces no inherent radiation of its own (some people erroneously assume this is black metal - though not exactly correct it is an easy way of looking at it. So you take this object and start heating it up. As it heats it starts to radiate. At lower temperatures it radiates low frequency (large Wavelength) radiation and as you heat it it continues through the radiation spectrum something like this:

Eimts from coolest to hotest, temps are approximates:

Radio Waves 1000K
Microwave
Infared Waves (i.e. below red or below visable spectrum) 2000K
Visable Light (4500k-7200K)
Ultraviolet (7500K - 20,000K)
X-ray (25,000K)
Gamma rays (30,000K +)

The temperatures provide for lightbulbs and the wavelength definitions are specifically peak outputs - i.e. where in the light spectrum the bulb will have its greatest output. This can be provided as a temperature (relating to a heated black body which would have the same peak - though not neccessarily the same color mix) or the specific wavelenght. The spectrum a bulb emits is usually referred to as the CRI (color rendering index) but let's leave that out for a moment.

The reason that actinics are not given in kelvins is that they typically are very narrow bandwidth i.e. they filter much of the output arround the peak wavelength - however, that does not mean that they don't have a peak wavelength or that the peak wavelength can not be directly related to a black-body object. The difference being that all the other wavelengths in the spectrum of an actinic are missing were as they are there in a black body object.

np on hijacking the thread - your input was valuable I just did not want folks to get a misunderstanding that the formula doesn't work - it does but the actinic bulbls are a bit of a special case and one has to be aware of how to apply the formula.

In my post by saying the bulb has a temperature of 6900K - I meant it has a peak output which would match a full spectrum bulb at the same temperature. Usually the peak is what we are interested in for organism health not so much for appearance - just so happens that many like the blue/violet tint of some of these bulbs as well.

Well - hope I helped and didn't add anymore confusion and I hope you enjoy the site I've posted.

Tom
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Old 02-24-2004, 03:06 PM   #3
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here's some good information

http://www.cameraguild.com/technology/kelvin.htm

A very good applet:
http://cat.sckans.edu/physics/black_body.htm
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Old 02-24-2004, 03:13 PM   #4
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Hey yaksplat - what's up - haven't seen you around much.

Don't like the cameraguild post - oversimplifies and misses a few important factors.

Like the second one - must use the same appelet as the one I posted

thanks for the additional info.
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Old 02-24-2004, 03:25 PM   #5
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Thanks for the help.

I'm in understanding of Wein's Law as it relates to Black Body but I meant to say that I can't see how it can apply to monochromatic light output like a an 'actinic' bulb where there's basically light from 400nm - 440nm but almost nothing else and a huge peak at 420.

I think the formula works for MH bulbs very well because the light is actually produced mostly by heat (some phosphors) but monochromatic flourescent bulbs just don't fit when the light is indirectly produced by exciting phosphors with UV light.

Hope I didn't come across wrong. I'm just always looking to learn.

Thank you!
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Old 02-24-2004, 03:28 PM   #6
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Old 02-24-2004, 03:30 PM   #7
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I haven't done any new DIY stuff for a while. I've been busy trying to figure out what exactly is in my tank. So many animals, so little time.

well, given the name Cameraguild, i knew that some of the physics of it would go right out the window. I was attempting to find sites that had nothing to do with cameras. I did like the graphs on this page.


So the question is, what is the optimal temperature bulb?

Does actinic filter the light, or produce light in the correct spectrum?
If actinic filters the light, then the remainder is being dissapated as heat instead of visible light. Wouldn't the organisms tend to use the portion of the spectrum that they need? Or do they need to be pummeled with that certain wavelength.

If we want to have our peak wavelength be at 420nm, then the color temperature should be around 7000K.

am i wrong?

Jim
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Old 02-24-2004, 04:22 PM   #8
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Yaksplat,

Some very good questions - some of mine as well. Actinics don't really filter but use gas combinations to get the phosphorous to emit a very specific band of light (narrow spectrum) - i.e. like mecury vapor in a standard flourescent and Argon and Halide in a MH bulb. Funny thing about these bulbs are that flourescents and MH are very similar in concept and infact both are gas-discharge bulbs but both use different ignition methods and different gas combinations.

I'm not so sure about what our reluctant charges really need, I guess it varies but I sort of think that we should attempt to replicate what they are exposed to in the wild rather than do stuff which makes them glow

Yep, your conversion is correct. Just always have to consider other stuff when using temp. even for MH bulbs - they do not give the same color spectrum as a black-body - it is only the peak that this relates to. You can tell this because a 20,000k object really will have very little visible light - but 20,000k MH's have tons of visible spectrum and with a very wide bandwidth (i.e. close to white light).

Tom
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Old 02-24-2004, 04:50 PM   #9
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Hey Tom,

I appreciate your comments on this. I think I understand better than before and that's always a good thing. Thanks for taking the time.

Yak - Actually, corals, or more precisely their zooxanthellae, can adapt to just about any light in the visual spectrum. It's not instant though. If you change the spectrum of your bulbs you should wait a week or two before judging the effect. I've heard theory that there are many species of zooxanthellae and each take advantage of certain wavelengths. I've also heard the other theory that zooxanthellae can actually adapt to different light sources.

bottom line - setup your lights with the look you like and let the corals adjust.

Actinic is just a made up name that Phillips lighting coined for one of their photo processing bulbs. In the hobby it refers to a bulb that produces light that peaks around the 420nm wavelength.

There are quite a few PC bulbs that just filter the light. the 7100K actinic is a primary example. These should be totally avoided IMO. They produce very little PAR compared to their true actinic counterparts that produce the light using rare earth phosphors.
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Old 02-24-2004, 11:53 PM   #10
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Menagerie, I have to agree with you...I am totally awed now! It's so great to have folks on here who really understand the science behind this stuff and are willing to take the time to explain it to those of us who don't. Kudos to all three of them!
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