LED lights

[Nebmaatra]

Looking for sound advice on LED lights. I have about 10 Paphs & a couple of prags under a 1000 watt LED on a 12 hour light cycle of which seem to be doing well. Miami is rather unforgiving when it comes to extreme temperatures & so I've brought them inside however Ive read about others who maintain 16 hour light cycles.
Any suggestions?

 

[naoki]

I'm not sure if the day (night) length is important for Paphs and Phrags (i.e., I'm not sure if they show photoperiodism). I usually don't change the duration between winter and summer, and they seem to be ok. If this is the case, you want to give enough light for the plants to grow. If you think that the light is the limiting factor (and if you want them to grow faster), then you can increase the day length.

Are you growing only these plants under 1000W? 1000W for a couple dozen plants seems to be an overkill. For paphs, I can easily cover 4'x2' area with 60-100W (mine is fairly efficient Cree CXB3590, each at 50W or efficient Sunritek T8-LED 4x 15W). Even if yours might be less efficient, 200W should be enough to cover 4'x2' area.

 

[Ray]

The only reason to increase the hours of exposure would be to compensate for lack of intensity, but if those are actual watts and not so-called "equivalent watts," there would be no reason for it.

 

[terryros]

I had to think that those were "equivalent watts". It is hard to imagine a true single LED tube or fixture that is 1000W. I grow about 40 Cattleyas under a total of 240 watts of LEDs.

I agree with Ray that with good light intensity from the LEDs, an indoor grower should try and approximate the photoperiod for the type of orchids. The broad range of tropical orchids don't receive more than 13.5 hours in the summer period or less than 10.5-11.0 hours in winter. Many that are more equatorial (Cattleyas, Phrags, Miltoniopsis) are in the 11.5-12.5 hours throughout the year. Giving more light than an orchid's genetic programming usually doesn't improve growth and may impair it. I run my plant room from 13.5 hours in peak summer to 11.0 hours in peak winter period in my room.


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[MorandiWine]

As previously mentioned its not the wattage but more the photonic output that counts. I see many LED manufacturers that still insist on using wattage as a gauge for how much light a unit will create. There simply is not a true formulation that will equate wattage with output. Factors like quality of the chips, efficiency of the power supplies, lenses, etc all will effect the efficacy of a unit.

Best way to tell if a light is giving you enough light is to get your hands on a Quantum Sensor and measure the PAR. PAR is a measure of photonic energy that is made by a source. Generally speaking plants fall into that range of measurement. Apogee makes a great unit for LED and other types of light, its just a little expensive. If you dont want to pony up for buying one, ask a photographer or perhaps a friend in the medicinal plant field, they would likely have something that will work.

Tyler


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[Bjorn]

Agree with the above, additionally there is one thing people should be aware of and that is the actual power supplied to the LED. With quite a few power supplies, particularly the cheap ones from China that you get on e-bay the current readings are way below specified. Why I know? I build my own LED setups and measure current on the power supplies as a precaution and observe a current in operation that is often only 50% of the rated current. The voltage is ok though so effec tive wattage from an e.g. 100W setup easily gets 50W.

 

[littlefrog]

I have observed very similar things when building lights.

Agree with the above, additionally there is one thing people should be aware of and that is the actual power supplied to the LED. With quite a few power supplies, particularly the cheap ones from China that you get on e-bay the current readings are way below specified. Why I know? I build my own LED setups and measure current on the power supplies as a precaution and observe a current in operation that is often only 50% of the rated current. The voltage is ok though so effec tive wattage from an e.g. 100W setup easily gets 50W.

 

[terryros]

I use and like the Apogee meter. Assuming manufacturers are being somewhat truthful, the light should specify the lumen output of the light. This does not tell you what portion of the light is in the photosynthetically active radiation (PAR) spectrum. The PAR meter is the simplest and best way a hobbyist can tell about the light intensity reaching an orchid.


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[MorandiWine]

I use and like the Apogee meter. Assuming manufacturers are being somewhat truthful, the light should specify the lumen output of the light. This does not tell you what portion of the light is in the photosynthetically active radiation (PAR) spectrum. The PAR meter is the simplest and best way a hobbyist can tell about the light intensity reaching an orchid.


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Apogee makes a quantum sensor that measures PAR. Lumens are almost worthless when it comes to growing plants because plants use more light than whats in the narrow lumen "field." A lumen is simply a measure of the amount of visible light for human eyes.


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[terryros]

Doesn't lumen output per watt tell us about the efficiency of the light? I agree that in the end, it is probably the PAR reading in the leaf zone of our plants that matters. But, we don't have much published information about the optimal PAR for various orchid types. When we extrapolate from sunlight/greenhouse conditions to LED lights, there is uncertainty. The PAR should be delivered within an optimal photoperiod for the type of orchid, so daily light integral (total photons over the day length) would be the most helpful and there is very little of this information with LEDs. Finally, LEDs can have lenses that create light that is more collimated (vertical) than diffuse light sources (including sunlight) and the PAR requirements for collimated light may be less than for diffuse light. Much work still needs to be done with LED lights and orchid growth and blooming.


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[MorandiWine]

Doesn't lumen output per watt tell us about the efficiency of the light? I agree that in the end, it is probably the PAR reading in the leaf zone of our plants that matters. But, we don't have much published information about the optimal PAR for various orchid types. When we extrapolate from sunlight/greenhouse conditions to LED lights, there is uncertainty. The PAR should be delivered within an optimal photoperiod for the type of orchid, so daily light integral (total photons over the day length) would be the most helpful and there is very little of this information with LEDs. Finally, LEDs can have lenses that create light that is more collimated (vertical) than diffuse light sources (including sunlight) and the PAR requirements for collimated light may be less than for diffuse light. Much work still needs to be done with LED lights and orchid growth and blooming.


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I agree that LED's are well under studied with orchids, makes sense since the orchid community still insists on using Foot Candles as a measure of light.

As for Lumens as a gauge of efficiency, not particularly unless you would use a calculation like lumens/watt but again PAR would be a more accurate unit of measure.

Tyler


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[naoki]

Agree with the above, additionally there is one thing people should be aware of and that is the actual power supplied to the LED. With quite a few power supplies, particularly the cheap ones from China that you get on e-bay the current readings are way below specified. Why I know? I build my own LED setups and measure current on the power supplies as a precaution and observe a current in operation that is often only 50% of the rated current. The voltage is ok though so effec tive wattage from an e.g. 100W setup easily gets 50W.

With these cheap eBay LEDs, when they say 100W COB, it usually means that it is the maximum input (decent LEDs don't market in this way any more). But we can choose whatever the current lower than the maximum. Most of us run very soft to increase the efficiency. So for DIY purpose, it isn't so harmful since we know this. But it is very misleading if this wattage rating is used for the assembled fixture (as others have said, there are many Chinese ones marketed in this way) since we don't know the actual wattage until you take the measurement.

Doesn't lumen output per watt tell us about the efficiency of the light?

Terry and Tyler, lumen per watt (luminous efficacy) can tell us something about the efficiency for plant growth. But we have to be careful since 1 lumen of light can contain different amount of PAR depending on the spectrum (I think both of you are saying the same thing). For plants, PAR photon efficacy (micro mol/J) is a bit more useful. However, if you are comparing two LEDs which share the same spectrum, then lumen/W can be used to compare the efficiency for plants.

If we know the actual emission spectrum from data sheet, we can easily convert lumen/W to micro mol/J or foot-candles to micro mol/m^2/s (i.e. normal light meter can give us approx PAR PPFD).

But if we limit the discussion to white LEDs, the difference in the conversion factors (lumen/W -> micromol/J) are not so huge (the maximum difference is around 18% or so). In other words, lumen/W can give a rough idea of efficiency for plants. In general, lower K (warmer) and higher CRI give more PAR per given lumen.