Many indoor growing operations rely on grow lights. These consume considerable energy. Much of the energy used to power the light is in frequencies that are not used for photosynthesis - rendering the greenhouse pleasantly bright, but not contributing to growth.

I propose that bright grow-LEDs be devised which pump all the energy into the red frequency used by chloroplasts. This would make greenhouses looks like photographic darkrooms. The leaves would look black, which is as it should be: reflected light is necessary for us to perceive color, and this light also reflects wasted electricity. Single spectrum LED growlights should markedly improve the energy efficiency of indoor growing operations.
-- bungston, Aug 02 2008

LED Growlight supplier http://www.fuzzlight.com/
[MisterQED, Aug 02 2008]

The Action Spectrum for Photosynthesis http://www.phschool...tosynth/action.html
An animated "experiment". [baconbrain, Aug 02 2008]

Relative absorption for a bunch of chemicals. http://www.citrusco...u/pic/46/c06_06.jpg
Your plant may vary. [baconbrain, Aug 02 2008]

LED Grow Lights http://www.myhydroponicgardening.com
LED Grow Light review - you need need blue,orange and red. [Orion79, Jul 07 2010]

chlorophyll a-b spectra http://en.wikipedia...ile:Chlorofilab.png
both clearly extend well into the UV [FlyingToaster, Jul 07 2010]

This is a good idea, nut not a new one. I will bun this anyway, till I can find proof, but I think the issue was either getting a LED to shine in the right frequency or that it wasn't a single frequency but a range.
-- MisterQED, Aug 02 2008


After a lurch around the internet, I now understand that chlorophyll isn't the only light-absorber, and that there are peaks in both blue and red light for the two types of chlorophyll, and other places for other chemicals (see links). So, a single frequency of red light is probably not the best thing for plants. Red and blue, if you want, as in the [MQED]'s link, or even more colors, depending on the plant.

I'm all for LED lights for efficiency, mind, even though plants only use about 10 percent of the energy that hits them. I have a pile of LED flashlights, and would love to see a LED growlight. Just not a red-only light. And the room will never look dark, no matter what you tweak--the plants just won't cooperate.
-- baconbrain, Aug 02 2008


I saw prototype LED growlamps many years ago at a space technology exhibition - this was before LED lighting had happened. They told me not to look directly at them if I turned them up, which of course I did having only seen low-power LEDs before. I had this LED matrix burned into my retina for hours.

I think choroplasts operate within a frequency range, rather than at a set frequency. In fact IIRC, plants have developed to prefer exactly the same spectrum as produced by the sun. Mimic that and that's the best you'll get.
-- wagster, Aug 02 2008


In my experience, you need red, blue, and even some orange light to get the most benefit from LED grow lights. When at the proper ratios, these lights will outperform HPS and MH by a big margin.
-- Orion79, Jul 07 2010


You don't need LEDs to do this. Fluorescent lamps (which are cheaper to buy, albeit less efficient to run) are doped with specific fluorophores on the inside of the glass. The lamp itself produces a lot of UV, and the fluorescent coatings are chosen to convert this into visible light.

Each coating emits light of only one colour (quite tightly), and standard fluorescent lamps contain a mix of fluorophores whose light, when combined, mimics white (or daylight, or whatever the manufacturer chooses).

So, there should be no problem to produce fluorescent lights which emit only those wavelengths which are useful for the plants. My guess is that the existing fluorescent plant lights have already been optimised in this way.
-- MaxwellBuchanan, Jul 07 2010


taking a look at chlorophyll-a, the absorption spectra seems to be mostly in the UV zone (though it peaks at violet)... so fluorescents with no or fewer fluorophores might be good.
-- FlyingToaster, Jul 07 2010


//chlorophyll-a, the absorption spectra seems to be mostly in the UV zone //

I suspect that the absorbtion peak in the UV is a non- productive one, and may even photobleach the chlorophyll.
-- MaxwellBuchanan, Jul 07 2010


A glow-right glow-light grow-light to grow-right.
-- MaxwellBuchanan, Jul 07 2010


I had to wipe off my kepyboard after I said that. Re doping: if you produce unnecessary radiation but then block it at the glass, the energy to produce has still been spent and so there is no energy savings.

I wonder if the UV absorbtion is protective, like melanin. Hanging around in the sun all day has got to be tough on the DNA.
-- bungston, Jul 07 2010


//Re doping: if you produce unnecessary radiation but then block it at the glass, the energy to produce has still been spent and so there is no energy savings.//

You're not blocking it. The fluorophores capture the UV and then emit light at a longer wavelength. I'm not sure of the efficiency, but I think it's quite high. (Also, glass absorbs a lot of UV, so it would be wasteful anyway if it were let out.)
-- MaxwellBuchanan, Jul 07 2010


//non-productive... photobleach// why and what ? <link>
-- FlyingToaster, Jul 07 2010


I may be wrong - it's been a while. But chlorophylls are complex molecules, and probably absorb light in several ways. Red light (like 680 or 700nm, which is what the reaction centres P680 and P700 are named after) provides enough energy to kick the right electron up and out of the molecule, which then starts a cascade of electron-passing which drives the reactions that ultimately make sugar.

UV light may be absorbed by a different part of the molecule, and is likely to kick out the wrong electron, effectively breaking the molecule. Photobleaching is what happens to dyed fabrics etc in sunshine - the dye molecules get broken by being kicked too hard.
-- MaxwellBuchanan, Jul 07 2010


I did not know about fluorophores. I wonder if they could be used on windows to augment sunlight in cloudy locales?
-- bungston, Jul 07 2010


This is a subject that could be discussed more easily by using simple units. I think only 3 classes are useful:

1. Energy: e.g. Joules, watts, and watts per unit area of electricity, light, or photosyntheses.

2. Numbers: e.g. moles of photons, total or per time/unit area.

3. Wavelength (or frequency) of light.

(Only two are strictly necessary, because energy and wavelength of photons are not independent.)

It's then easy to understand why a wavelength around 650-700 nm is best for powering photosynthesis. This is where watts of photosynthesis per watt of light is greatest by far. Why? Because a joule of such (red) light provides far more photons than a joule of (e.g.) blue light, and photosynthesis is a quantum event - its rate is governed by the number of photons harvested, not by their energy.

The commonly seen graphs of the photosynthetic action spectrum are misleading in this sense, because they are equal quantum flux graphs, not equal power graphs. An equal power PAS graph shows blue light as far less effective per watt; in fact, blue is not necessarily much better per watt than green (depending on the plant's accessory pigments)! (Absorption spectra are even more misleading, because, as [MaxwellBuchanan] pointed out, absorption is not the same as use.)

Interestingly, this is of little importance with fluorescents, because they are also quantum devices, and exhibit exactly the reverse bias. A mole of UV photons produces a mole (less efficiency loss) of either blue or red photons, and thus the rate of photosynthesis per watt of electricity is about the same; which is why fluorescents aimed at plant growth have a good amount of both red and blue.

But long wavelength LEDs produce more moles per joule, which is directly reflected in the relationship between operating voltage and frequency; so red LEDs are highly efficient at driving photosynthesis.

Other wavelengths are needed to influence the plants' growth responses, but not in the same quantities.

So you would expect good LED grow lights to have predominantly red LEDs, with lesser amounts of other wavelengths (particularly blue, to control phototaxis and etiolation). Which they do.
-- spidermother, Dec 21 2012



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