# Can plants use green light?



## gf225

Do plants use the green part of the spectrum?

I assumed not but an ADA advert on the back of an English Aqua Journal (36) says,



> "Aquatic plants have evolved over millions of years to adapt to greenish light available to them."


Is there any truth in this?


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## Left C

I not sure if ADA is referring to this or not. If plants appear green, it means that some, most or all of the green spectrum is being reflected back and not absorbed, *but there are some accessory pigments that can use some of the green spectrum.*

Here is a good article about photosynthesis and the following is quoted from it:
"A pigment is any substance that absorbs light. The color of the pigment comes from the wavelengths of light reflected (in other words, those not absorbed). Chlorophyll, the green pigment common to all photosynthetic cells, absorbs all wavelengths of visible light except green, which it reflects to be detected by our eyes. Black pigments absorb all of the wavelengths that strike them. White pigments/lighter colors reflect all or almost all of the energy striking them. Pigments have their own characteristic absorption spectra, the absorption pattern of a given pigment.

Chlorophyll is a complex molecule. Several modifications of chlorophyll occur among plants and other photosynthetic organisms. All photosynthetic organisms (plants, certain protistans, prochlorobacteria, and cyanobacteria) have chlorophyll a. *Accessory pigments absorb energy that chlorophyll a does not absorb. Accessory pigments include chlorophyll b (also c, d, and e in algae and protistans), xanthophylls, and carotenoids (such as beta-carotene).* Chlorophyll a absorbs its energy from the Violet-Blue and Reddish orange-Red wavelengths, and little from the intermediate (Green-Yellow-Orange) wavelengths.

*Carotenoids and chlorophyll b absorb some of the energy in the green wavelength.* Why not so much in the orange and yellow wavelengths? Both chlorophylls also absorb in the orange-red end of the spectrum (with longer wavelengths and lower energy). The origins of photosynthetic organisms in the sea may account for this. Shorter wavelengths (with more energy) do not penetrate much below 5 meters deep in sea water. The ability to absorb some energy from the longer (hence more penetrating) wavelengths might have been an advantage to early photosynthetic algae that were not able to be in the upper (photic) zone of the sea all the time."


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## hoppycalif

I keep hoping one of our more science minded members will do some good testing to verify what colors of light plants can use effectively. It would be a difficult test to set up, but very interesting. I think if I were to try this, and I won't, I would try to use lights deficient in certain wave length bands, but with constant wattage and bulb type. Finding such lights would be a real project. I have always wondered just how correct we are when we say actinic bulbs are of little or no use to our plants, so that would be one test I would want to see done. Another is the green light test. Who wants to volunteer?


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## ryzilla

I remember in bio 101 3 semesters ago stating that something like 520 - 565(nm) is reflected by plants. Im guessing this holds true for most but what about red a white pigmented leaves?


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## rs79

Plants can absorb ANY visble light. Red and blue may be optimal but strong green light will actually work.

There's a book "Lighting for plant growth" (Kent State Press) that delves into this in great depth - it's the PhD work of the guys that invented the Gro Lux bulb.


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## hoppycalif

rs79 said:


> Plants can absorb ANY visble light. Red and blue may be optimal but strong green light will actually work.
> 
> There's a book "Lighting for plant growth" (Kent State Press) that delves into this in great depth - it's the PhD work of the guys that invented the Gro Lux bulb.


That makes a lot of sense, since plant leaves can't possibly reflect all of the incident light at any wave length. The green leaves look green because some of the green light is reflected, but that hardly means that all, or even most of it is reflected.

Does, that book say anything about actinic lights? They are blue, so it seems that plants should be able to use a lot of it.


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## Dave Spencer

When I look at my plants I can see various shades of green. This would suggest to me that certain areas of the green part of the spectrum must be getting used to produce this variation.

Dave.


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## ruki

The chart from the article is pretty nice.









From this, one might conclude that green is mostly, if not totally irrelevant in regards to photosynthesis, so leaf patterns in the greens don't really matter and just get carried along in the genome as noise.

A related question I have is why a naturally occurring plant leaf ever be red, since this seems to be a disadvantage. This doesn't count the selectively bred plants which provide a considerable number of the red aquatic plants available to us.

The natural follow-up question is how much red light can be utilized by red leaved plants. Or stated another way is how much does being red interfere with photosynthesis.

Since this is directly address conventional photosynthesis there should be research on this. If red leaved plants can utilize red light then we have some reason to assume that this could possibly work for green light as well.


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## Newt

Here's a different chart showing chlorophyll a and b absorption thru the visible spectrum:










Now are we talking just GREEN plants or ANY plant in general as I think there could be a difference with red pigmented plants,yellow pigmented plants, etc.


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## rs79

"From this, one might conclude that green is mostly, if not totally irrelevant in regards to photosynthesis"

Look at it again. Between 500 (green) and 600 (yellow) there's a huge spike in Phycocyanin.

But, plants don't behave like pigments in a test tube which is where those numbers came from.

Go get a $2 tube, plug it in then observe what your plants do. Don't be too freaked out if they grow a bit better - the tube is new and going to be brighter for the first few weeks of its life then slow down as anode decay reduces luminous flux over the life of the tube.

Doesn't matter what color the plants are. It's not like you need different colot tubes to grow different color plants. You'll just never see that mantioned. What you will see mentioned is "needs BRIGHT light". 4 warm whites beats 1 Gro Lux any day...


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## ruki

And what type of aquarium plants is Phycoerythrin important for?


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## Newt

Why...............Blue Green Algae, of course.


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## rs79

Doesn't matter. Rather than sit there and stare at graphs and charts try some nasty cheap cool whites which are mostly green and notice how well the plants do. I have. They work fine.

There's really no point in arguing against this unless you've tried it. You're just guessing...

Again, the numbers for chlorophyll absorbtion were chemicals in from test tubes. Try using real plants.


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## hoppycalif

Testing the effect of various wave lengths of light on plants is probably very interesting, and if done well, might even provide good information to know. But, other things, like fertilizers and CO2 have much more effect than light spectra for the bulbs we would want to use. One exception is the actinic bulbs used for salt water tanks. I still would like to see where someone has carefully tested to see if those are good, bad, or otherwise for freshwater plants.


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## rs79

Actinics don't work in freshwater tanks for growing plants.

Or rather, they haven't so far.


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## hoppycalif

rs79 said:


> Actinics don't work in freshwater tanks for growing plants.
> 
> Or rather, they haven't so far.


I have read and heard that said many times, but I still haven't seen any write-up of experiments done to demonstrate that. (I repeat that statement to others too, but I'm a bit nervous about doing so.)


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## rs79

People on the APD list over the past 20 years or so have tried them. Nobody did it for very long, the plants pretty much go on vacation.


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## ramskip

Found some new research to shed light on this old thread...pun most certainly intended ;0)

"The majority of green light is useful in photosynthesis" -Michigan State University 

Seems like current research supports the fact that green light has an effect on photosynthesis! Kinda cool...and although surprising, Pluto also used to be a planet, so that's science for ya


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## niko

Plants can't use green light all right. But here's a strange observation:

Tank with green water + bacterial bloom. Water so murky and so green that you can not see anything that is further than 1/2" from the glass. No CO2. No ferts. PAR on the bottom is 10-20 without the green/murky water. With the green/murky water is 0 because the depth is 2 feet.

2.5 months. Water cleared by itself.

Plants had grown immensely. In pea green/murky brown water. The light that managed to reach the plants went through a thick green/brown filter.

Analyze that.


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## ramskip

niko said:


> Plants can't use green light all right.


Plants do use green light. See my previous post with scientific proof. End of story.


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## Seattle_Aquarist

Hi All,

GSAS invited Cara Wade from BuildMyLED to Seattle last fall for a talk. According to her Dr. Bugy, the well known Photo-biologist with Utah State University did an experiment in 2014 where plants were grown under various spectrums ranging from blue and violet through the yellows, greens, and reds and if the PPFD (light intensity aka PAR) of the various spectrums are equal there is no noticeable difference in the growth of the plants.

I also learned that plants photosynthesize not just in the "A" and "B" spectrums but throughout the PAR range.

It was a very good talk, very informative, it is unfortunate the BML is no longer doing aquarium lighting.


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## Skizhx

Plants do use light in the green spectrum. This actually isn't a new discovery either, and emphasizes just how behind the science this hobby has fallen. 

Plants use a combination of pigments combined into complexes intended to harvest photon energy. Energy absorbed by these complexes can be accumulated between multiple complexes in an additive fashion to provide energy for photosynthesis. As a result, energy from most light wavelengths can, and is harvested. Plants are also fairly adaptive in allocating energy and resources to adapt to different conditions, and are well capable of tolerating less than ideal growthconditions. Of course, the less stress, the better...


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