Switching to led's

[Terryros]

I have been seriously growing Cattleyas under LED lights for at least 5 years. Growing and blooming them is now good, after having studied and experimented with various growing conditions. The lights for my Cattleyas are all ALT brand, either 15 or 20 watts, with 60 degree beam angles. They are natural white and screw into track lighting fixtures. They are more expensive, but they have excellent heat dissipation. I agree with Ray’s calculations. I only use a PAR (photosynthetically active radiation) monitor to assess the amount of photons/light. I do not use more than 300 micromoles/m2/sec at the top of any Cattleya. I use day lengths that replicate what Cattleyas see in the wild, so a maximum of 13 hours in peak summer and a minimum of 11.0 hours in mid-winter. I have an orchid friend in another state who is using the same light levels and day lengths and successfully growing/blooming Cattleyas.

[raybark]

Thanks for the update, Terry.

What do you use for determining the PAR light level?

[Terryros]

I use an Apogee Quantum Flux meter, set to electric. I use it on Sample mode to obtain instantaneous readings. I don’t use an attached wand, just the sampling cell on the top of the meter. Considering all of the other expenses of this hobby, it was a reasonable price to be able to figure out accurately what different plants need. Foot candle meters aren’t accurate enough for the most important kind of light, but the approximation that you give for converting foot candles to photon flux is a start. As you have pointed out better than any one on the various discussion boards, targeting the traditional literature peak foot candles and maintaining those for an entire daylength during under-light growing is giving at least double the needed light.

[Aquii Finn]

The thing that I don't understand about your responses is the apparent assumption that because no one has responded affirmatively that they have grown and bloomed catts - specifically - under LEDs, that it is taking a risk to grow them that way.

the more i research led's the more confused i get....many people say they put out a lot of photons in general..I also understand that the first generation of led growlight tech, being the red and blue lights, had serious shortcomings in both flowering orchids and in other non botanical growth, ...the new generation led's are full spectrum white or mix red blue and white bulbs, but I still have no idea or have heard yet, that they work on flowering catts...I was hoping to gain from someone else's experience, so as to not lose any by experimenting...sorry for the trouble...

[raybark]

I think the initial problems were simply due to insufficient intensity. Because the output was fairly narrow bands of red and blue light, commonly-used light meters were (and are) lousy at telling the user what the output was. Foot-candles are measures of light as perceived by the eye, which is mostly in the central, yellow-green parts of the visible spectrum, so that's what the meters read. A plant uses the entire visible spectrum, but absorbs especially well in the red and blue regions.

From a plant health perspective, and for maximum growth, large-scale production operations still rely on red/blue lighting, and white is usually only added to make it easier on the workers. When I switched to LEDs, I originally used Philips red/blue production units, and have raised plants from flask to blooming under them with no problem, simply by using the recommended maximum foot-candle recommendations for the plants and dividing by 10 to determine the PAR lighting (PPFD) for 12-16 hours per day. (One of the benefits to under-light growing is that you can vary distance and time to reach the plant's needs.) I soon got tired of the appearance of the plants, and switched to their white/far red version. I was much happier and the plants carried on with no apparent change.

Going back to my earlier comments, I am quite certain that if you set up LEDs covering the growing area uniformly with 200 µmol/m²/sec PPFD, your plants would thrive.

[Terryros]

I thought that I was clear that I have been successfully growing and flowering Cattleyas under “natural white” LED lights for about 5 years using peak light levels not more than 300 micromoles/m2/sec and daylengths seasonally adjusted between 11 and 13 hours. LEDs do work very well for Cattleyas!

[Aquii Finn]

I thought that I was clear that I have been successfully growing and flowering Cattleyas under “natural white” LED lights for about 5 years using peak light levels not more than 300 micromoles/m2/sec and daylengths seasonally adjusted between 11 and 13 hours. LEDs do work very well for Cattleyas!

Thank you very much Raybark and Terryros! I missed page 2 as i didn't know it was there....I still have to figure out the conversions and what micromoles are etc....but thank you so much for the info!

[Terryros]

Photosynthetically active radiation (PAR) quantifies photons in the wave length range that supplies photosynthesis. You need a PAR meter to measure this way. A standard foot candle meter usually measures additional wavelengths, so the reading isn’t as precise for what plants specifically need. However, the ratio of 5:1 foot candles to PAR peak photon density may be a rough approximation. If 300 peak photon density is the most that you should need for constant lighting over the course of a day, that would be roughly 1500 foot candles. I think it is important to remember that many orchids are sensitive to day length and giving them more or less day length than they are genetically programmed to want may inhibit best growth or blooming. The range from 11.0 - 13.0 day length will satisfy any Cattleya. An indoor light grower can give this exactly. A green house grower in northern latitudes is mostly stuck with long day length in the summer. In the winter, they can give supplemental light to keep to a minimum of 11.0 hours.

The daily light integral for my Cattleyas varies from about 10 to 12 moles/m2 over the course of the year. This is consistent with a few other reports of PAR light exposure for higher light orchids in green house conditions. Ray’s calculations work in an indoor plant room with LED lights.

[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.