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Discussion Starter · #1 ·
All these light colors are also quite confusing with several articles indicating differing opinions. There are some articles which say color is a matter of preference and does not really matter to plants. Others say colors with a greater red spectrum is better for vertical plant growth while blue is better for horizontal growth. Others still say the higher the color K, the better.

So does color affect plant growth? Using standard (non-aquatic) fluorescents as specific examples, would using "cool white" lights (4000k) be worse / better / no different that using "daylight" lights (6000k)?

Thanks for illuminating me on this (pun intended). :)
 

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I cant give you any deffinite answer but IME lower K means more algae growth along with a yellowish tint to your tank. I switched to a higher K and the plants grow as well but algae doesn't.
 

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IronLoach said:
All these light colors are also quite confusing with several articles indicating differing opinions.
One answer is right: You can't tell at all how a plant will grow just with the Kelvin number.

But..

There are some articles which say color is a matter of preference and does not really matter to plants.
This is wrong. The spectrum and the intensity of the light in certain areas of the spectrum, not the kelvin-color, will affect both photosynthetic activity and growth-patterns.

If the lamp hits hard at the chlorophyll (blue and red) the photosynthesis will be driven harder and thereby faster growth.

Very small nuances in the far-red portion of the spectrum will trigger different types of growth. Under billions of years the plants that grow the tallest and fastest when shaded (one type of far-red to red ratio) could quickly reach up to unshaded bluish sky-light (another type of far-red to red ratio). These nuances can't be red from a spectrum (I think) because the nuances are smaller than the spectrum plots measure.

But from a spectrum and knowing how much intensity the bulb manages to output from the energy you put into the bulb you can with the photosynthesis action spectrum calculate the "PUR-efficiency" - how hard the bulb will drive photosynthesis if reaching the plant.

(With lumens+watt you can calculate how well the spectrum conforms to the photooptic curve and thereby you know how much intensity you get from the bulb - how energy efficient the bulb is to output lumens. This efficiency factor can then be used to calculate how much energy conforms to the photosynthesis action spectrum.)

This is what Ivo Busko have done here:
http://www.aquabotanic.com/lightcompare.htm

I have made a PUR-efficiencty calculator in Java and have begun extending his list here:
http://194.236.255.117/defblog/permalink/1402.html
 

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Discussion Starter · #4 ·
wow def, i think i hurt my head trying absorb all that scientific stuff. never thought lighting could be so complicated.

i also came across this statement at the krib -

And don't be fooled by the fact that "daylight" bulbs don't look as bright as "cool-white" bulbs, since cool-whites put out the highest intensity in the frequencies where your eyes are more sensitive, which are not the most useful frequncies for photosynthesis. Any "daylight" or "full-spectrum" bulb will do.
So in general terms, does this mean that daylights (6000k up) are better than cool whites (about 4000k)?
 

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And don't be fooled by the fact that "daylight" bulbs don't look as bright as "cool-white" bulbs, since cool-whites put out the highest intensity in the frequencies where your eyes are more sensitive, which are not the most useful frequncies for photosynthesis. Any "daylight" or "full-spectrum" bulb will do.
The problem with this quote is that it speaks in too general terms. "Cool-whites" is a whole range of bulbs where some kan be extremely efficient while others are not. The same thing with "daylight" and "fullspectrum".

Those words are just a semantic description of the color, and not the specific details of the actual spectrum.

To be more specific I would choose (if I couldn't calculate PUR-efficiency) a fullspectrum bulb with tri-phosphours signature: Three sharp spikes in the red, green and blue portion of the spectrum, like so:




Why? Because theese tri-phosphor-signature are not filtered as much as "whole-spectrum-bulbs" like Osram Biolux. Those spikes will hit very hard at the chlorophyll. Filtered bulbs doesn't reach the same intensities where it matters the most.

Thus, smooth spectrums are bad because it comes with a price of less intensity, like so:


So in general terms, does this mean that cool whites (4000k) are better than daylights (6000k)?
Can't say just from the Kelvin-rating.
 

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Discussion Starter · #7 ·
Hey, defdac, thanks again so much for your informative post. Appreciate it much. It gave me a much broader understanding of color, lumens, PUR, PAR and stuff. I hope others like me who are in the dark get enlightened by your post.
 

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Chlorophyll A only uses 2 types of light, p680(so called red) and p700(so called far red), all the light energy with less nm(or higher energy) is going to filter down to these two light harvesting complexes.

Blue light eventually will work it's way down and lose energy in the process before being used. Blue will cause some plants to open their stomata more, I really have never seen any research done specifically o aquatic plants nor aquatic plants being grown under CO2 enrichment that open their stomata further when the blue light is added. There is some blue light added to a cool white bulb, not as much as some, but still, it's there.
Will this increase plant growth? Not at the end of the day IME, IMO and the research shows this as well.

There was a study done to test the differences in terms of growth with the cool whites and so called speciality bulbs, they performed the same.
www.Aquabotanica.com has it there.

In simpler terms:

I've never found much practical differences between a cool white(4100K) and say a 6500K dylight bulb, the daylight bulb did make the plants appear better to my eye.

The researcher's did good work when I review the article, you would have a rough time dissproving their findings.

I often will use a cheaper warmer colored bulb and then a high K bulb for nice mix. A triton and cool white are nice mix. K does not really tell you much, those graphical spikes are much better/useful.
But often it's mainly marketing rather than practical test in planted aquariums or large scale growing or ornamental aquarium plants/Tissue culture etc.

My friend at UF, Dr Kane uses cool whites.

I like nice color for my eyes, I use 5000K and maybe a 6500-8800K range bulb, you can use a 10K bulb also mixed with a 5000K.

It(Color temps) matter much less than all the tech stuff suggest.
Don't be blinded.

Regards,
Tom Barr
 

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Discussion Starter · #9 ·
Thanks as usual Tom. Personally trying to follow your regimen policies when it comes to plants (except for dosing specific individual nutrients - too cumbersome for me now). By the way, the aquabotanica link is dead. tried googling but only found the german version.
 

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No, not that, this was a research paper done comparing cool whites to specialty grow bulbs where they found no significant differences between the plant growth rates with the bulbs.

Some plants such as Hydrilla have no stomata, so blue light will not cause the stomata to open further.

I do not know of any studies done on submersed aquatic plants that suggest their stomata open further when exposed to blue light vs red etc.

Also, with an enriched CO2 content, the in/out of gases may be dramatically influenced.
This influence is far greater than a slight increase in stomatal aperature I would argue certain.

Imagine breathing in a thick medium like water. Consider that if you increased the O2 levels 10X, would that help you to pull the dissolved gas in better with less energy?

A similar thing occurs with water/CO2 with plants.
In air, the stomatal aperature may play a much larger role than in the aquatic environment.

I'll try to find the article.
I emailed Robert to see if he knows where it is.

Regards,
Tom Barr
 
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