Switching to led's

[raybark]

A "mole" is Avogadro's Number of something - 6.023x10²³. A µmol is ¹/_1,000,000 of that.

An excerpt from my October newsletter:

If you look at published culture sheets for orchids, you will see light recommendations along the lines of "1000–1500 foot-candles". The first thing we need to understand is that those numbers and units are a recommendation for the maximum amount of sunlight to which the plant should be exposed, and that if we are utilizing artificial lighting for the same dawn–to–dusk time period, the intensity should be approximately half that. To see the explanation of that, READ THIS, but the basic concept is that we are trying to match the total quantity (intensity X time) of light received at a constant intensity, rather than starting at zero at dawn, reaching a peak at noon and returning to zero at dusk.

Among horticultural professionals, that "total quantity" is known as the DLI, or "daily light integral". It is the sum of the photons hitting the plant over a complete day, and is expressed as the quantity of photons (moles) per area (square meters) per time unit (day). The rate at which light hits the plants is known as the PPFD, or photosynthetic photon flux density,and that is expressed as micromoles per square meter per second (µmol/m²/sec).

Don't be freaked out by these terms, the conversion from foot-candles to PPFD is simple: full sun has an intensity of approximately 10,020 foot-candles at noon on a clear day, which is equivalent to 2000 µmol/m²/sec, making the conversion factor 0.2, so our "1000–1500 foot-candles" maximum becomes 200 to 300 µmol/m²/sec, suggesting that artificial lighting of about 100–150 µmol/m²/sec, when used for 12-14 hours would be plenty. In other words, if translating from a "maximum sunlight" recommendation in foot-candles to PPFD of artificial lighting, just divide by 10!

[Dorsetman]

I have all my catts ( about 3-400) under lights.they are on a bench 5 feet wide and near 30 feet long. There is some natural light, but my greenhouse lies between a high hedge and a tall trellis heavily planted with climbers and shrubs , to hide it. I have five lights, each on its own light track , running across the bench from side to side , and also extending across the gangways at each side of the bench and then just about lighting the side benches , which have other orchids on them. Four of my lights are 600 watt ballasted twin spectrum lights,and the fifth is a 240 watt led array. The height above the plants is different, and the led has a wider angle spread and is much lower. You will understand that the lights run back and forth, non stop.
I can’t see any difference in growth between thosee under one kind of lamp and those under the other.

[Mike H]

If your an AOS member you can view this article in Orchids magazine.
https://secure.aos.org/digital-libra...efault.aspx#48

---------- Post Merged at 09:29 AM ----------

The author says he has successfully flowered Cattleya as well as other orchids under LED.
If your not an AOS member JOIN! (I have no affiliation with AOS)

[Mike H]

Do your research so you understand what your getting, then research it a bit more.
Then track your setup and share with us all your results.
Most of all enjoy the journey.

[Dorsetman]

I am very late looking at this thread - unusually I have an hour with nothing to do (!)..
But with a long narrow growing area, why not use a light track, and send your single lamp back and forth ? You then use much more light than you would want, but average it out because the light comes and goes. I have used this system - yes on my cats - for several years now. The lights are in fact as near to the plants as I can get them - those with tall spikes ( schombocatts and L.autumnalis etc ) have to be placed carefully so that they are not chopped off by the lights.
I have a large growing space - maybe almost 30 feet a over 5 feet , and I have several tracks running across this space, in fact 2 metre ( 6 ft 8inch) tracks, so that the light also reaches beyond the growing space, lights up the paths at either side, and also the front part of the two side benches.. ( A 30 foot track would be an impossibility - elec' supply connections for one reason ). My lamps are all 600 watt "dual spectrum" Bayer bulbs, apart from one 240watt LED array.

[Aquii Finn]

I went with 2 amare sp 400's and a single cobb led in between, to cover the 12' x 3' area. The single cobb should be good for seedlings and paphs i hope...with the catts under the amare's on both ends...plenty of light, no burnt spots yet....I do have a cat eldorado for the first time producing 2 buds under these leds...so happy for that, but it has only been 4 weeks...i hope it is an eldorado actually and fun to see the color variety if it is...

[Dorsetman]

Eldorado is, I believe, now wallissii - the old rule of priority. Pity, I think eldorado a much more romantic name.
One of my favourite species - L am on the lookout for varieties . I have v.coerulea on order at present.

[Masaccio]

Could I add another question here, that could be relevant to a standard-sized cattleya grower? That would be the rate of fall-off from LEDs, which, according to my PAR meter, seems sharp. Ray, I know you would know, or have good comments on this (and thank you on my own behalf for the great information you provided in this post). Aquii Finn, I too have just converted to LEDs and used to grow standard cattleyas under HID - mine was only 500 watts (250 MH + 250 HPS) all the time. I share your hesitancy and concerns about LEDs. I've just started a collection for my new LED setup, and in the cattleya department only have a seedling C. trianae, and a C. violacea, both of which are doing just fine under ordinary outside spotlights (26 watt 250 watt eq). The trianae is rooting like crazy and re-established itself post-repotting in no time. So I would say yes, enough light for cattleyas theoretically, but with the caveat of falloff making standard cats more of a challenge. I hope to hear what Ray has to say about this because I have no experience with taller plants as yet. Thanks.

Oops. I didn't notice several pages of great responses before I posted my question. Great thread!

[raybark]

Light is light. No matter how it is produced, the "fall-off rate" is the inverse-square - 2x the distance = 1/4 the intensity, 3x = 1/9, etc. However, the configuration of the lamp and the reflector all make a difference in what gets to the plant, meaning there is no easy way to calculate that for comparative purposes.

For example, a 2' T5HO fluorescent and a LED floodlight may have the exact same initial light output, but the former is spread out over two feet of length and radiates from the entire surface of the tube, with some of the light projected directly at the plant, some scattered sideways, some reflected down to them, and some reflected back into itself, so is lost. The light from the LED spot, on the other hand, emanates from a very small area mostly facing the plants, and is enclosed in a far more efficient reflector package, so far more of the light energy actually gets to the plants.

I suspect that the reason the drop off seems greater with the LEDs is because there is far less scattered light for your meter to capture than there was with your HID setup. Personally, I'd set the height based upon the measurements near the tops of the plants. Your multi-lamp setup ought to be great for complete coverage.

[Masaccio]

Cool. Thank you, Ray.