Huh? LEDs with UV output? 2

[MikeHalloran]

I was watching Extreme Survival Bunkers on the Travel Channel just now.

One bunker is a former missile silo, intended to be self-sustaining, converted to real nice condos. All of the video was apparently shot before occupancy, and before painting of staircases, etc. was done, but it's a serious project that has cost $15 million so far.

The entrepeneur who masterminded the development proudly showed us his hydroponic growing room, with no crops started yet, and told us that the plants will be nourished by mineral solutions, with LEDs in the overhead to provide photosynthesis with very little electrical power required.

I don't know much about LEDs, but I don't remember them having significant UV output.

Did I miss a meeting?


Mike Halloran
Pembroke Pines, FL, USA

 

[ScottyUK]

Some 'white' LEDs actually emit UV light. A phosphor within the device absorbs UV and emits visible light. I can't remember the name for this spectral shift - Stokes Shift maybe? Physics class seems such a long time ago.

 

[itsmoked]

Why are you concerned about UV? Plants don't want any part of UV. They want A particular red and a weeeee bit of a particular blue.

There are UV LEDs. They are not efficient or very strong and would not typically be used for creating some other color.

Currently blue LEDs are phosphor converted to yellow and mixed to provide white.

Scotty: Are you sure you're not confusing fluorescent lights here? They definitely are designed to generate UV via the excited mercury vapor. The UV is then down converted via a mix of phosphors to provide the various whites available.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[VEBill]

Wiki

 

[OperaHouse]

Nature will find a way to use almost any energy. I was growing plabts with ultrasonic sound. Surprised that never took off with a practical application.

 

[btrueblood]

What VE1BLL said. I had a sample sent me of an AlGaN UV LED about 5-7 years ago. Wish I knew what I did with it, as I have occasional uses for UV sources.

 

[IRstuff]

Reptiles love UV.

Depending on what one calls "UV", plants can be happy in the near-UV/blue regime:

http://www.botany.uwc.ac.za/ecotree/photosynthesis/spectrum.htm

TTFN
faq731-376

Need help writing a question or understanding a reply? forum1529

 

[VEBill]

I ordered 100 LEDs off the website of a Hong Kong based reseller. There were ten unmarked bags of ten LEDs each. Some of the LEDs were clear/transparent, so I had to power them up to see what colour they were. All the usual Red, Green, Blue, and White. Then I powered one up and it was Red [I began to mark 'Red' on the bag], ...then Green, ...then Blue, in a repeating pattern. I wasn't expecting that. The next one was the same except after several of the slow RGB cycles, it went into what I'll call the Disco mode where it started a miniature Disco-style RGB light show. It was amusing for those that are easily amused.

I missed the memo on those ones.

PS: The same vendor sells UV and IR Flashlights.

 

[mcgyvr]

Photosynthesis typically occurs in the 400-700nm range (not UV) UV is damaging to most cells/tissues.
Many of the new LED plant lights output approx 660nm and 460nm (red/blue)

There are numerous UV and low cost "near" UV LED's in the 340-420nm range out there (many marketed as a "true violet" color).. They typically can't tolerate as much current as there "non-UV" counterparts and typically suffer from short lifespan due to the shorter wavelengths "destroying" the dome over the LED die.

 

[ScottyUK]

Hi Keith,

You made me wonder if I was losing it up top - from the Wiki entry by people who know more about this than I do....

"There are two primary ways of producing white light-emitting diodes (WLEDs), LEDs that generate high-intensity white light. One is to use individual LEDs that emit three primary colors —red, green, and blue—and then mix all the colors to form white light. The other is to use a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light, much in the same way a fluorescent light bulb works."

Not sure if that proves my sanity though!

 

[cranky108]

I did some experments a few years ago with a "black light", as a side light, and it did appear the plants were leaning in that direction. Since then I have been using a red/blue led mix, and have had better results than with full spectrum "plant lights". The 14 W/sq ft seem to work. However I am using premade modules so I haven't revisited the more closer UV colors.

The biggest problem is the plants look black, so I have a hard time determinig there health without a flash light.

A recent gardening book suggests 64 6X4 garden plots is all that is needed for a family of 4, so for one family this is 1536 sq ft of gardening space, and 21.504 kW of light.

Hardly what I call sustanable without the grid.

 

[MacGyverS2000]

420nm and 680nm (give or take), that's what plants want... not UV. And there are plenty of strong (relative term, obviously) UV LEDs out there... I use a batch of them for UV-cured sealants, and they do the job in a few seconds for thinner pots (dentists use something similar to cure dental work).

On a side note, late last year I was working on updating our business cards for recruiting efforts. The cards include a number of hidden challenges on them, from perceptible binary watermarks to UV-printed source code, which prompted a search for cheap UV LED keychain lights. To determine the proper wavelength needed for the ink being used, I sourced a few bare LEDs from the usual locations (Mouser, DigiKey, etc.). The proper wavelength LEDs were $15 each... insane pricing, and no way we could hand out a business card (which cost $1.50 itself) with a $15+ keychain light and still make marketing budget. After multiple attempts with different companies (who sent us keychains using wavelengths too far off of the mark), we finally found one that could make them for about $0.60/pc. We now spend about $3/dandidate while recruiting. Still trying to figure out how one company can get away with sub-$0.50 LEDs when everyone else is charging 30 times that... but the lesson is you can find what you need if you look long enough.

Dan - Owner

http://www.Hi-TecDesigns.com