# Plant light spectrum



## Justinkscott (Jun 18, 2011)

I've read a lot of forum posts talking about total quantity of light reaching the plants being important.

However, the other day I stopped into a local hydroponics place and got to talking to the owner. She talked about light spectrums as ways of convincing the plants to do different things.

As an example, she said that when she wants the plants to focus on growing their roots and stems, she uses primarily blue light spectrum. When she what's them to fruit, she uses primarily red light. 

She also said that plants can't see the mid-range spectrum at all as it is green light. In fact she uses green light when she needs to tend to her "sleeping plants". Green seems to be a large component of many 6500k (daylight) bulbs, isn't it?

A lot of what she said made conceptual sense; but I wonder if we have any studies or experiments that might lead us to the same or similar conclusions?

Thanks!


Sent from my iPhone using Tapatalk


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## Hoppy (Dec 24, 2005)

It is very well known that aquatic plants use light from different parts of the spectrum more or less efficiently than from other parts. And, it seems to be true that plants that tend to be red, are more vividly red when the light used has lots of red in its spectrum. But, you can't direct the growth of aquatic plants by manipulating the light spectrum - blue for roots, red for leaves, yellow for polka dots, etc. First, and most important, you need enough total light in the 400-700 nm region of the spectrum for the plants to grow at all. Then, if you want the plants to look their best, you may want to use more red, or blue, or magenta to get the best coloration of the plants. (Plants do use green light, just not as much of it, as efficiently, as other parts of the spectrum.)


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## BruceF (Aug 5, 2011)

I think she is right. There is a lot of horticultural literature regarding light but not much in the aquatic plants field.


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## jeffkrol (Jun 5, 2013)

Justinkscott said:


> I've read a lot of forum posts talking about total quantity of light reaching the plants being important.
> 
> However, the other day I stopped into a local hydroponics place and got to talking to the owner. She talked about light spectrums as ways of convincing the plants to do different things.
> 
> ...


Synopsis:
http://hortsci.ashspublications.org/content/43/7/1951.full
http://hortsci.ashspublications.org/content/43/7/1951.full.pdf

you can modify plant behavior by changing environmental conditions (or adding chemicals such as plant hormones) but it is complicated... and can be species specific.. In our world this is not as important as "general" all around plant growth.


> Perhaps
> LEDs used as supplements to sunlight or
> other types of lighting in greenhouses or
> growth chambers could modify crop growth
> ...


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## Raymond S. (Dec 29, 2012)

But exactly where is this leading ?
I have found that one particular bulb grows plants better for me. It is listed as being 5000K. Oddly the horticulture industry now favors 5400K over 6500K bulbs.
Most manufacturers of bulbs don't give any chart/graphs showing the spectrums of
their bulbs but Zoo Med does. Their "Flora sun" bulb has light in the 650nm range(red)
as well as the other more common range. I attribute this red light from them as being the reason that I get better growth from them.
However: They have rather dim light compared to other bulbs. So I always use them in conjunction/w a 6500K or in a taller tank a 10,000K bulb.
For what it's worth, as we speak, I have a ten g tank/w one in it. There are two bulbs in it and the other one is their "Tropical sun bulb" (T8/not available in T5) and they are in seperate fixtures at front and back of the tank. The leaves on the plants face the front of the tank and would not if the Flora sun bulb were not providing much more of what the plant needs. The Flora sun bulb is in the front.
The plant facing the bulb which contains the red part of the spectrum isn't conclusive.
But it speaks real loud.


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## jeffkrol (Jun 5, 2013)

Raymond S. said:


> But exactly where is this leading ?


I think what the o/p was alluding to is controlling plants.. Say (and I can attest to this personally) you have a plant that is growing very compact ( i.e my Water wysteria) w little inter node elongation... (very bright actinic/10000k hybrid LED driven on full for long daylight period)
Adding red (which w/ a well designed LED set is quite easy) would only involve brightening or dimming a channel. In this case dimming the "blue" channel in favor of the 660nm red channel (or increasing red intensity) caused the plants to "stretch"....

This type of manipulation has been known for a long time.. Want spindly tall plants, grow them under incandescent...

The current "science" is to manipulate the plants to do things like increase biomass, increase nutrient/antioxidant levels, ward off disease, open stomata, or darken color, initiate fruit or flower production, to name a few..with as few "watts" as necessary to achieve those goals. 
Most of which are really not "that" important for aquariums on a general level (few eat their aquatics).... 

Of course you have esthetics to consider as well........


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## jeffkrol (Jun 5, 2013)

Raymond S. said:


> It is listed as being 5000K. Oddly the horticulture industry now favors 5400K over 6500K bulbs.


Color temp is a convient way to express things but not very "functional"..
...............


> Color temperature (Kelvin) refers only to the visual appearance of a light source—
> Unless the light source
> has a continuous spectral distribution, its color temperature alone may not be reliable as a means of
> selecting a suitable correction filter. For example, fluorescent lamps do not have the continuous smooth spectral distribution
> ...


http://www.theodoropoulos.info/attachments/076_kodak03_Nature-of-Light.pdf


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## hbosman (Oct 5, 2006)

Raymond S. said:


> But exactly where is this leading ?
> I have found that one particular bulb grows plants better for me. It is listed as being 5000K. Oddly the horticulture industry now favors 5400K over 6500K bulbs.
> Most manufacturers of bulbs don't give any chart/graphs showing the spectrums of
> their bulbs but Zoo Med does. Their "Flora sun" bulb has light in the 650nm range(red)
> ...




Check this site out for graphs on different bulbs. I've been using Giesmann aquaflora and mid day bulbs. They have been extremely popular in the planted tank arena. I also like the GE 6500k (Starcoat). Very high PAR and the color just looks more like natural sunlight to me. The Giesmann Mid Day looks a little too yellow to me. But that's just a personal opinion, there's plenty that would disagree.


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## Raymond S. (Dec 29, 2012)

In a T5 bulb I find the True Lumen Flora to be glare free and give my tank the most lifelike, natural colors. I'll look up the defenition of color temp as you are over my head on that one. I just(for now) think tthat the 5000K Zoo Med Flora sun doesn't have 
the part of the psectrum over that rating. And that it grows my plants better than any that I've tried so far. I'm suspicious of those windows. You would think that the particular bulb mentioned would therefor hav more light in the remaining spectrum which it has...a higher percent of a more limited amount of the whole spectrum.
Don't know how to do this in less words sorry.
But an actinic bulb has very little or none of the rest of the spectrum.
Therefor when in a two bulb system, you change one out for an actinic, you loose more of the rest of the spectrum than you gain in that actinic color.
So with one actinic and one 6500 you have less overall light than the plant has with two of the 6500 bulbs.
My question is...I have a 650nm bulb along/w a 6700K bulb. Did it work the same in this case. Did I loose more than I gained ? I had two 6700K before.


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## foster (Sep 23, 2012)

I'm with Raymond on the ZooMed bulbs. I use a combination of 1 5500, 1 10,000, and 2 6500K T-8 ZooMed bulbs. I get better growth, and color from those bulbs than I do from 6500K HO bulbs. And lots less algae issues. I firmly believe that the red spectrum helps tremendously.


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## jeffkrol (Jun 5, 2013)

Raymond S. said:


> .
> But an actinic bulb has very little or none of the rest of the spectrum.
> Therefor when in a two bulb system, you change one out for an actinic, you loose more of the rest of the spectrum than you gain in that actinic color.
> So with one actinic and one 6500 you have less overall light than the plant has with two of the 6500 bulbs.


You have to define "actinic" .. actinic just means "can develop film".. 
It is another terrible term.......
As to "Common useage" in the aquarium biz..
420nm... See where it would "fit" in the photosynthetic chart below..
much of the "rest of the spectrum" is inefficient.
Interesting discussion and it shows the "problem" w/ using the term "actinic"....
"Actinic bulbs provide light in the blue wavelengths which is easily utilized by plants during photosynthesis. Blue light on its own will make plants more compact and bushy. Some actinics are specific in wavelength output; namely 460nm. These bulbs are just off the absorbtion curve for for plant photosynthesis"
http://www.aquaticplantcentral.com/forumapc/lighting/80568-plant-grow-actinic.html

Thinking a bit more about this and , w/ the lack of another inhibiting factor (nutrients ect.) or not well defined synergies an "actinic" bulb could produce light that is 100% photosynthetically active, where a 6500k will be lucky to produce 50% efficiency..


Raymond S. said:


> My question is...I have a 650nm bulb along/w a 6700K bulb. Did it work the same in this case. Did I loose more than I gained ? I had two 6700K before.


You sacrificed "active" blue for "active" red... Considering red is a bit more stimulative you could "gain".. You lose some of the intermediate colors.. blue,bluegreen, ect and of course some visual "neutrality"..












> Both chlorophylls _a_ and _b_ primarily absorb red and blue light, the colors most effective in photosynthesis. They reflect or transmit green light, which is why leaves appear green. The ratio of chlorophyll _a_ to chlorophyll _b_ in the chloroplast is 3:1.


That ratio is pretty "generic" btw.. Env. conditions can change it..


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## jeffkrol (Jun 5, 2013)

Considering every thing above , you could achieve 6500K using just RGB LED's but it would be the least efficient way to do it.......










W/ blue in only one chlorophyll range, green not worth much, and some "good red"............. 

Again comparing it to a "white" LED, which is barely better...










Though to be fair both seem to "work"......


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## sowNreap (Jun 10, 2012)

Several months ago I swapped one of my 6500k Home Depot T8 bulbs for a Zoo-Med Flora Sun (so have 1-Flora Sun & 1-6500k). I have no proof that it grows plants better than than 6500k bulb although I think it should. I do know it makes my tank look so much better ...to me at least. Seems to tone down the bright light of the 6500k bulb.


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## Raymond S. (Dec 29, 2012)

I lately read an article which stated that in a two bulb system/w two 6500K bulbs
if you swap out one for an actinic(460nm) you must only consider the Actinic to be 30% of your PAR that you will then receive. Seems as though the band width is so small on the actinic that you are really loosing a lot of the light that a plant could use.
Because what ever it is that actually makes the light is much more specific/fine tuned.
I was presuming that the same holds true for the Red 650nm one.
So in my T5 tank when I now use one @ 6700K and one @ 650nm I lost overall
quantity but gained in a specific color that the plants use.
Since you have been talking good about the Actinic color for plants I went into the secret locker and dug out the Coralife 50/50 10,000/460nm bulb in T8 and put it into the t8 tank along with the Zoo Med 5000K one. Now it has bright white and blue and red in there. I'll give it three weeks to see if I get a flood of algae before deciding to keep it in there. This has been a very helpful thread...thanks to all who contributed.
I cultivate algae so I've been two years finding bulbs that will do it for me in my tank without flooding it out/w the algae...just a slow steady growth of it. Well I found that but now I will try this 50/50 for a while also just to see.
I started a T5 tank(these are ten g tanks BTW) and only have changed bulbs twice so far but I still have a couple of weeks to go before making an assesment of the bulbs I am now using...one 6700K and one 650nm. But I think this thread will cut my time on this one a lot to get to where I grow the algae slow and steady.


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## jeffkrol (Jun 5, 2013)

Raymond S. said:


> I lately read an article which stated that in a two bulb system/w two 6500K bulbs
> if you swap out one for an actinic(460nm) you must only consider the Actinic to be 30% of your PAR that you will then receive. Seems as though the band width is so small on the actinic that you are really loosing a lot of the light that a plant could use.


I'd agrue that point a bit.. but it is hard w/out the "actinic" to be defined by a wavelength specification.. correctly designed an actinic light would have a high efficiency in stimulating photosynthesis..and I can't imagine where it would be "less" than a 6500k bulb, knowing that a good deal of the spectrum is in the less "efficient" range... Now there are "other things" i.e ancillary pigments that would be "starved" of light in a pure actinic environment though. 









From left to right;

1. UV 405-415 1x 3w
2. UV 420-425 1x 3w
3. RB 440nm 4x 3w (maybe 5x)
4. RB 450-455 4x 3w (maybe 5x)
Green line is NW 4x 3w (maybe 5x)
White slopes highlight the output spectrum of OCW 3up chips 2x





Raymond S. said:


> I was presuming that the same holds true for the Red 650nm one.


Errr.. no..I don't see either being "true"........ 
re: Corals .. but much applies:


> Overall though corals are fairly tolerant about what light they receive, although I've seen studies that show corals under only red light will die, however corals under only blue light will thrive, so perhaps there's not much to that "need" of red light. But the best thing to do is to find what you like as far as color spectrum, and if you're unsure, make sure whatever setup you get allows you to dim various channels so you can fine tune your color spectrum, while a lot of fixtures allow you to tune a "white" and a "blue" channel some newer ones are adding violets and other colors to the spectrum.


http://www.bareefers.org/forum/inde...scussion-in-full-spectrum-led-concepts.14120/

There are good reasons for this.








http://hortamericas.blogspot.com/2012/06/grower-looks-to-increase-efficiency.html
A bit more:
http://www.illumitex.com/illumitex-leds/surexi-horticulture-leds/

F6 wavelength distribution
Blue (400-500nm)	49.5%
Green (500-600nm)	0.5%
Red (600-700nm)	49.9%
Far Red (700-799nm)	0.1










> Best for Vegetative Growth
> The F6 spectrum has an enhanced blue region and provides the fastest vegetative growth results. The increased blue content reduces plant height, thereby improving plant appearance and space utilization. Recommended for the production of leafy green vegetables.


I am ignoring "aesthetics" for now.....


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