Question about UV LED fluorescence

[Brainiac]

Hello,I'm new to the physics forum.I have a question regarding fluorescence,and I didn't know where to post it exactly,so I decided to do it here...
I like growing plants,and am forced to grow them under artificial lights during winter.I am always on the lookout for more efficient lights,that is,those that produce more light per watt consumed.I was reading about LED diodes,they are the most energy efficient,but their light spectrum is too narrow for plants to grow healthy under them...
Then I started thinking if maybe UV LEDs could produce a full spectrum light as black light from them energies fluorescent materials.If I were to insert a whole bunch of them into a phosphor tube normally used for fluorescent lights,would fluorescence light of the phosphor coating then have the full spectrum needed for plants to grow? And would intensity of it be worth it?

 

[davenn]

Hi Brainiac

firstly, welcome to PF :)

I personally cannot answer the Q. that's an interesting one which would also be applicable to my freshwater tropical aquarium
will be interested to see the answers that come forth. I'm getting sick of the high cost of 2 fluoro tubes every 12 months $40 each

Dave

 

[CWatters]

I've never grown plants under artificial light but Google suggests you don't actually want a wide spectrum, you want one that targeted...

http://en.wikipedia.org/wiki/Grow_light#LED

LEDs allow production of bright and long-lasting grow lights that emit only the wavelengths of light corresponding to the absorption peaks of a plant's typical photochemical processes.

snip

Recent developments (2014) in the design of correctly tuned LED modules optimize the blue and red energy produced by the LED to closely match the plant requirements for optimum growth.

snip

It is also often published that for vegetative growth, blue LEDs are preferred, where the light has a wavelength in the mid-400 nm (nanometer) range. For growing fruits or flowers, a greater proportion of red LEDs is considered preferable, with light very near 600-640 nm, the exact number this wavelength being more critical than for the blue LED.[12] (Actually the cited reference says it uses exactly three wavelength, 470 nm, 612 nm and 660 nm, the 612 nm one targeting not photosynthesis as such but carotenoids.)

 

[SredniVashtar]

White LEDs are usually blue or ultraviolet LEDs with one or more phospors that 'downstep' the frequency of a portion of their light to produce an overall 'whitish' light. Hence your idea of using phosphor coating in the same way fluorescent tubes do is qualitatively correct. Fluorescent tubes and CFL uses UV in the 350 nm range, IIRC. White LEDs can use blue or UV light with one, two, three or four different phosphors to create different spectra. As a general rule, the 'better' the white, the less efficient is the lamp. Building your own conversion system is IMO a waste of time: just buy the right white (and or colored LED) for your needs.
Also, white light can be produced with LEDs in different colors (not necessarily R G B). What is best usually depends on the 'eyes' of the beholders, that is your plants.

Here you can compare different spectra for commercial products.
http://www.popularmechanics.com/tec...scent-vs-led-ultimate-light-bulb-test#slide-1

 

[Veneficus]

Hi Brainiac,

Before I answer, I am obligated to full disclosure: I work at one of the product development sites of Philips, though not in the Lighting sector.

I do know about Philips Lighting offering special solutions for e.g. greenhouses, all done with specially tuned LEDs, like CWatters mentioned. I also know that the desired wavelength(s) depends on the exact application, for instances whether you want to grow flowers or fruit.

Some info can be found here:

http://www.lighting.philips.com/main/application_areas/horticultural/greenhouses.wpd

It's probably possible to build them yourself if you know your way around a soldering iron and electronics.

 

[SredniVashtar]

Veneficus, since you happen to be in the knows - so to speak - can you spare an opinion on LED droop? Every now and then a research group comes up claiming to have fond the 'true' and 'definitive' cause. Is it mostly due to auger recombination (is this the Lumiled 'current') or is it mostly due to electron leakage (Schubertian 'current') in your opinion? What about DADR?

Sorry to hijack this thread, but I see you are online right now...

 

[Veneficus]

Hi Sredni,

Sorry to disappoint you, but as I mentioned, I'm not in the Lighting division and my knowledge of those details is limited to the basics of (organic) LEDs. I happen to know about the applications because I've had some contact with the people involved at Philips Research.

 

[SredniVashtar]

Hi Sredni,

Sorry to disappoint you, but as I mentioned, I'm not in the Lighting division.

LOL, sorry, in my haste I read what I wanted to read. :-]

Thanks anyway.

 

[Brainiac]

Thanks guys for all your replies.I think I should've been more clear of what I need,I need an artificial light source that mimics the sun as closely as possible,I don't think any visible spectrum LEDs can do that.I mean,to get the same spectrum of light provided by fluorescent and HID lights with LEDs you would need like a 1000 of them and each glowing at a different wavelength,since,as I understood,LED diodes glow at a specific wavelength,but maybe I didn't get that right? Also,LED growth panels are too expensive (at least here where I live) and glow with purple-ish color,which is unappealing to the eye(MY...eye). UV LEDs probably also glow at a specific wavelength,but I was wondering if fluorescence caused by them would give off a wider range of light wavelengths that plants would be able to utilize. I guess that depends on the fluorescent material being used? I'd conduct an experiment,but I have no idea how to "measure" what light wavelengths are in there...

 

[SredniVashtar]

Solar radiation's spectrum has considerable infrared (IR) and ultraviolet (UV) portions. LEDs are designed to cut away those two parts for efficiency and safety reasons - the whole point of going LED with respect to incandescent lighting, for example, is to do away with the unwanted heating - that is IR radiation, of traditional light bulbs. Likewise, you don't want the UV part of the spectrum that might cause skin cancer.
Luckily, you can attain almost the same chromatic effect, at least in the eyes of humans, without those IR and UV tails.
LED lighting for agricultural purposes is a... blossoming field (double pun intended) and it is reasonable to believe that it is possible to design LED lamps capable of reproducing a reasonable replica of the spectrum plants need.

But spectral fidelity is only half of the story: intensity is the other. If you want to reproduce the same amount of energy per unit area and per unit time the sun is giving us, well, you must be prepared to use a lot of power (that is many LEDs) and/or to place your lamps veeeeery close to your plants.

 

[Brainiac]

Solar radiation's spectrum has considerable infrared (IR) and ultraviolet (UV) portions. LEDs are designed to cut away those two parts for efficiency and safety reasons - the whole point of going LED with respect to incandescent lighting, for example, is to do away with the unwanted heating - that is IR radiation, of traditional light bulbs. Likewise, you don't want the UV part of the spectrum that might cause skin cancer.
Luckily, you can attain almost the same chromatic effect, at least in the eyes of humans, without those IR and UV tails.
LED lighting for agricultural purposes is a... blossoming field (double pun intended) and it is reasonable to believe that it is possible to design LED lamps capable of reproducing a reasonable replica of the spectrum plants need.

But spectral fidelity is only half of the story: intensity is the other. If you want to reproduce the same amount of energy per unit area and per unit time the sun is giving us, well, you must be prepared to use a lot of power (that is many LEDs) and/or to place your lamps veeeeery close to your plants.

Yes you are right,we don't need any of that useless IR,but a little UV is good for some plants.I know there are lot of LED panels intended for plant growing,but I think they are not yet perfected,because some plants might grow well under them,but others don't.(also...the price...)Since I have many different species,I need that "universal" light that has a wide range of wavelengths.The question remains would those UV diodes do the job.Oh and no,I don't want to also match sun's intensity,that's really hard to do,but having lights as close to plants as possible is very useful,since the intensity drastically decreases with increasing distance between them.Uh I sure hope those guys poking around overunity succeed. (haha that word is so unaccepted it's even marked as misspelled). Because the whole point at the end is decreasing electricity bill...

 

[Vagn]

Thanks guys for all your replies.I think I should've been more clear of what I need,I need an artificial light source that mimics the sun as closely as possible,I don't think any visible spectrum LEDs can do that.I mean,to get the same spectrum of light provided by fluorescent and HID lights with LEDs you would need like a 1000 of them and each glowing at a different wavelength,since,as I understood,LED diodes glow at a specific wavelength,but maybe I didn't get that right? Also,LED growth panels are too expensive (at least here where I live) and glow with purple-ish color,which is unappealing to the eye(MY...eye). UV LEDs probably also glow at a specific wavelength,but I was wondering if fluorescence caused by them would give off a wider range of light wavelengths that plants would be able to utilize. I guess that depends on the fluorescent material being used? I'd conduct an experiment,but I have no idea how to "measure" what light wavelengths are in there...

It might be better looking for the sort of system solar panels are tested with. These are generally calibrated to produce something (reasonably) close to the solar spectrum. Such devices are called solar simulators, and it's very difficult to get a good fit.

 

[CWatters]

Quite a few LED manufacturers claim high Colour Rendering Index, many better than a fluorescent tube.