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Lighting technical. Kelvins and spectrums usable by plants.
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Moment
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Joined: 06 Mar 2007

PostPosted: 2007.03.11(Sun)12:35    Post subject: Lighting technical. Kelvins and spectrums usable by plants. Reply with quote

So I have the power issue out of the way.

78 watts over 30g is going to be plenty. 2.6 watts per gallon to be exact. That comes with the understanding that CO2 will be needed at around 20+ppm. Also with the knowledge that KH will have to be maintained in case of DIY CO2 fluctuations. Add to all that its a good idea to aerate at night to accentuate the plant respiration cycle, and provide vital oxygen to fish. Pretty much sum up last topic?

OK then lets get technical. Lets get onto specifics about bulbs.

I mentioned some in my last topic about spectrum's plants need. We likely have all come to the understanding that plants need red and blue spectrum primarily as source of energy for photosynthesis. Specifically in the ranges around 630nM for red and 430 nM for blue. PAR range or "Photosynthetically Active Radiation"

My digging has determined that kelvins or color temperature compares to spectrum in that the lower the kelvins the more relative power in the lower red end of spectrum and vice versa... High kelvins mean more relative power in blue end of spectrum.

Due to the mixture of phosphors in a bulb, any bulb can have spikes in a given range.

Example. Powerglo is 18000k has major bulk in blue area with spike at 420 but has large spike in red at 620 and decent coverage of range 650 to 680.

I'm sure this is a good bulb to stimulate needs in blue range but just due to its 18000k temp it doesn't have as much relative power in red.

The Lifeglo doesn't either. It has temp of 6700k. Though it can be said that 6700k has more relative power in red most all the light in this bulb is in green area of spectrum which plants actually reflect around 500nM. Its brighter then ol'heck though! 3000 lumens per 39w tube! That is because human are most sensitive to light in green area.

This is a good article to start on. http://www.sunmastergrowlamps.com/SunmLightandPlants.html

This page has a nice picture of the color output at different kelvins (color temp.
http://www.techmind.org/colour/coltemp.html

What I want is a 39w T5 bulb that has an even lower than 6700k color temp. Something that is powerful in red area. I've got the blue I feel I need in the Powerglo, even some spiking in red.

I know Rex you recommend 5000k-10000k. Can you debunk my logic please. 5000k is likely strong in red so that's sounds good. Where would I get a T5 bulb like that?

Everyone elses thoughts too please.
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Minsc
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Joined: 03 Jan 2006
Location: Framingham, Mass

PostPosted: 2007.03.11(Sun)14:48    Post subject: Reply with quote

Bulbs in the 5000-10,000k range give off light that looks good to the human eye.
A study was found recently that indicated that bulbs described as "white", typically in the 2000-4000 range often will have a better spectrum available to the plant. However, they look absolutely terrible over a tank, and if a tank looks awful, that pretty much ruins the whole point!

Grab a good daylight bulb and enjoy the tank, the plants will do just fine.
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Minsc
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PostPosted: 2007.03.11(Sun)15:26    Post subject: Reply with quote

Found the link:http://www.barrreport.com/general-plant-topics/2540-cool-white-fls-lighting.html?

You might want to check out the rest of the website as well. If you are this interested in spectrums and PAR, I think you will like delving into Tom's work.
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Moment
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PostPosted: 2007.03.11(Sun)15:30    Post subject: Reply with quote

Ya but that isn't exactly scientifically specific is it. Kinda blunt, not much fun. LOL. Not to mention it's oversimplified and not 100% accurate.

It's not a specific kelvin that looks good to human eye, it's specific wavelengths. Certain bulbs at temperatures like say 5000 - 10000 may emit any amount of those wavelengths. That much is true. And what you said is partly true since the wavelength that humans see best will be at its highest relative power somewhere between 5000k-10000k.

Plants don't see what humans see. I am merely trying to in an obsessive compulsive manner (LOL) discuss what temp of light contains the most relative power beneficial to plants.
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PostPosted: 2007.03.11(Sun)15:32    Post subject: Reply with quote

Refering to your most recent comment>>> Cool I will look at that site. Thanks
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PostPosted: 2007.03.11(Sun)15:39    Post subject: Reply with quote

http://www.uaf.edu/coop-ext/publications/freepubs/HGA-00432.html

That is the direct link to the article you are mentioning. It is good. I think everyone should have a look at it. Though its not exactly on my topic either.
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hedgelj
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PostPosted: 2007.03.11(Sun)16:18    Post subject: Reply with quote

OK,

Not to completely shoot you down here but most of those diagrams are only applicable to brand new lights. The signals degrade over ttime. Also, any floating organics, or any chemical within your water will also degrade the signal. That is b/c any chemical has its own absorption spectrum and will absorb and reflect some of the light. Secondly, what about the reflection and absorption of the light by the water itself? That is why most SW tanks use light that is greater then 10K Kelvin because as you go down farther the wavelengths don't have the power to make it down that far to the reef.

Plants are very adaptable. If we were talking about SPS corals or clams or any other very high light SW organism then perhaps....it may be relevant. However, there are many more applicable variables to worry about in a FW tank. The lighting is that important.
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Moment
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PostPosted: 2007.03.11(Sun)16:29    Post subject: Reply with quote

OK OK so what is the drift of what you are saying? You don't think my subject is valid? It's just a topic. I'm not trying to cure cancer.

Well, in the form of rebuttals... First these are new bulbs I'm talking about. Secondly T5 bulbs are said to actually burn out before they lose their spectrum... AND... those other variables you talked about are there no matter what bulb you use sooo... I do think it is a viable topic.

Just basically want to start with good bulb. Every bulb, no matter how good or crappy, is going to meet the same resistance. Every car on the road drives the same road but some do it much faster or handle much better. We are not talking about the road, we are trying to compare cars.
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PostPosted: 2007.03.11(Sun)16:53    Post subject: Reply with quote

Now that I've reread the article, I see it isn't quite as specific as I remember. Ah well, it is still interesting.

I can vaguely remember someone doing spectrum comparisons of actual commercially available bulbs, but I may be mistaken. Maybe you want to take that one on? I'm sure quite a few people would be interested.
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PostPosted: 2007.03.11(Sun)17:22    Post subject: Reply with quote

I know the article you are talking about, this is it.

http://www.aquabotanic.com/lightcompare.htm

I learned a lot there. there and the articles I sited above. Basically scroll down to the charts and you want the bulbs with highest PAR efficiency. It would really help to read and find out what PAR is and what PAR efficiency is.

Like a perfect example is if you look in chart with the Hagen bulbs you will see that the Powerglo has higher PAR efficiency than Hagens own plant bulb the Floraglo. Primarily because of the combination of phosphors.

Comment?
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