fluorescent grow lights

[clusty]

Hey,

I am starting to prepare my artificial lighting setup for my orchids and had a few questions:
Think it might be possible to approach the 3000fc mark needed for Cattleyas with 2 3' T5HO horticultural fluo tubes. I am thinking of 2 since was thinking it might be a good idea to have a 2700k and a 6500k tube.

Any other advice would be greatly appreciated.

[naoki]

Clusty, 3000fc frequently mentioned for Cattleya is the measurement of peak intensity of sun light (around noon) in the greenhouse. With artificial light, you can give constant light, so you can be ok with weaker light. Also, comparison of different light source by "footcandle" is not so meaningful. This is because photosynthetically usable radiation (PUR) per footcandle is influenced by the spectra.

Just for your info, this is the kind of fc you can get from T5HO. Here is some measurement I took:
http://www.orchidboard.com/community...tml#post572079

Here is Rosemadder's measurement:
http://www.orchidboard.com/community...tml#post572076

Ray's measurement:
Measuring Florescent light output

But many people can grow Cattleya under T5HO. I think most people use >4 bulbs to cover 2" width of the growing area. So if you are placing the plants close to the bulbs (without over-heating the leaves), 2 bulbs may work to cover 1 row of Cattleyas. I usually grow lower-light orchids, but started to grow Cattleya alliance under T5HO. I place high light plants so that the leaves are less than 6-inches from the bulbs (I use only 6500K). So, I'm giving 1200-2000fc, but they seem to grow ok. Here is one which flowered in this set up:
Laelia alvaroana

[clusty]

Thanks a bunch for the reply. It is exactly what I needed.

I was curious about the "math" of hours vs light strength. As long as you don't go over say 15h, is 1000fc for 10h the same as 2000fc for 5h as far as plants are concerned?

[tropterrarium]

Re Naoki's point that culture sheets give peak intensity, whereas with all day grow lights you can get away with less intensity is spot on. As a first approximation, to get same amount of photons over the course of a day, you can cut the peak intensity in half for constant light source. Essentially, you convert area under a bell curve to a rectangle and calculate hight of bell curve = peak intensity vs. hight of rectangle = constant light.

For math, see http://www.aos.org/default.aspx?id=516 second part of that contribution. Notice, that AOS switched the captions for the two figures!

[naoki]

Thanks for the link to AOS article.

Generally, you can compensate the intensity by more hour. But there are several caveats.

One caveat with regard to equating 1000fc for 10h with 2000fc for 5h is that the photosynthetic rate usually saturates as you increase the light intensity. When the light is relatively weak (compared to the max intensity which the plant can handle), then the relationships is relatively linear, and the equation may work.

page 54 of the following page has a figure:
docs\lectsupl\Light\light

Similarly in CAM plants, they absorb and store the CO2 during the night, and this storage capacity may be the limiting factor (rather than cumulative amount of light per day).

Finally, some orchids may be photoperiodic (meaning they use the length of night as the indicator of season).

[clusty]

So a rough calculation:
Assume plants is about 4" under, 2 bulbs give 2000FC running for 12h should be enough for cattleyas.
I have a bunch of baby phals, that could also grow in between I guess.

Does this make sense?

[rick84]

For the price of a fluro set-up, why not just get 15w led grow bulb. 100% full PAR and no worries about burning. you are wasting your money on electricity to power each of these 23w? t-5 tube. T-5's are generally a HO(high output) and each 2' bulb generates 5000 lumens. Of that 5k the plant will only get so much based on the distance from the bulb. Yes t-5 don't get as hot as other types of grow lights but they still generate some heat, and why would you want a light right on top of your plants. (that makes me nervous) Not only that but there are wavelengths that plant don't use or barely use any.

Photosynthesis is the ability of plants to absorb the energy of light, and convert it into energy for the plant. To do this, plants have pigment molecules which absorb the energy of light very well. The pigment responsible for most light-harvesting by plants is chlorophyll, a green pigment. The green color indicates that it is absorbing all the non-green light-- the blues (~425-450 nm), the reds and yellows (600-700 nm). Red and yellow light is longer wavelength, lower energy light, while the blue light is higher energy. In between the two is green light (~500-550 nm). It seems strange that plants would harvest the lower energy red light instead of the higher energy green light, unless you consider that, like all life, plants first evolved in the ocean. Sea water quickly absorbs the high-energy blue and green light, so that only the lower energy, longer wavelength red light can penetrate into the ocean. Since early plants and still most plant-life today, lived in the ocean, optimizing their pigments to absorb the reds and yellows that were present in ocean water was most effective. While the ability to capture the highest energy blue light was retained, the inability to harvest green light appears to be a consequence of the need to be able to absorb the lower energy of red light.

Plants also use multiple variants of chlorophyll, as well as accessory pigments such as carotenoids (which give carrots their orange color) to tune themselves to absorbing different wavelengths of light. That makes it impossible to assign a single wavelength of best absorption for all plants. All plants, however, has chlorophyll a, which absorbs most strongly at ~450 nm, or a bright blue color. This wavelength is strong in natural sunlight, and somewhat present in incandescent lights, but is very weak in traditional fluorescent lights. Special plant lights increase the amount of light of this wavelength that they produce. But a 400-500 nm wavelength bulb wouldn't be enough, since many plants take cues for germination, flowering, and growth from the presence of red light as well. Good plant lights produce red light as well, giving plants all the wavelengths of light they need for proper growth.

---------- Post added at 10:33 AM ---------- Previous post was at 10:28 AM ----------

The sun emits a full-spectrum white light, most of which is unused by plants. Over time plants have evolved like people, to respond to light between the wavelengths of 400-700nm, which is known as the PAR (Photosynthetically Active Radiation) region. Even though plants receive the same spectrum year-round under the sun, over time they developed sensitivities to individual wavelengths of light they utilize better than others. These wavelengths are the Holy Grail for grow lights, as they supply over 90% of the energy used for photosynthesis by Chlorophyll A and B during both the vegetative and bloom stages.












Photosynthesis and LED Grow Light Spectrum


Chlorophyll A and B are the two primary compounds responsible for photosynthesis. These compounds absorb wavelengths of light with the highest efficiency at 439nm and 469nm blue, and 642nm and 667nm red. Aside from Chlorophyll A & B, there are other accessory light-harvesting pigments, most notably carotenoids, which absorb light with the highest efficiency at 439nm and 483nm blue. The other less noted pigments such as xanthrophylls, account for less than 5% of the energy supplied for photosynthesis, and absorb small quantities of light in the 480nm – 620nm region. Since Chlorophyll A & B along with Carotenoids supply over 95% of the energy necessary for photosynthesis, these are the only wavelengths a properly-tuned LED grow light should focus on for the greatest results.

Testing has shown that the only horticultural lights capable of creating such fine-tuned spectral outputs are LED Grow Lights. By focusing the nm output of each LED to a corresponding wavelength absorption point (like 642nm), the rates of photosynthesis can be increased dramatically over full-spectrum lighting. Testing has also shown that if you do not focus directly on the wavelength absorption point (ie: using a 625nm or 630nm instead of 642nm) you will have dramatically lowered rates of photosynthesis by comparison. For these reasons you want to focus on making sure whichever grow light you purchase comes as close as possible to 439nm, 469nm, 483nm, 642nm, and 667nm.

[clusty]

Originally Posted by rick84

For the price of a fluro set-up, why not just get 15w led grow bulb. 100% full PAR and no worries about burning. you are wasting your money on electricity to power each of these 23w? t-5 tube. T-5's are generally a HO(high output) and each 2' bulb generates 5000 lumens.

I wanted LED's but I would pay about 200$ for some LEDs that have 5000 lumen output. The same in fluo costs about 40-50$

[rick84]

when it comes to led's don't worry about the lumen or foot candle. Worry about wattage. Again 15w is enough.
Led's have to be a minimum of 12 watts to be powerful enough to penetrate the plants tissue. And the best led's have a 5w diode. More power, more penetration, the farther away the light is placed.

---------- Post added at 12:14 PM ---------- Previous post was at 12:12 PM ----------

....

[rick84]

this is my 600w commercial led tunable wavelength=$750.00 I have plans on a very large collection.