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How much PAR are your orchids getting?

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troy

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I use t-8s, my light duration is 13 hours 45 minutes. hope you texans are doing ok!!
 

naoki

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Well, different species get different amount, but mine is between 60-240 micro mol/m^2/s for 13 h. Paphs, Phals are around 100 micromol/m^2/s, Cattleya at the higher end. In terms of daily light integral (DLI), they are getting 2.8-11.2 mol/m^2/d.
 

terryros

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My Phals and Paphs are at 50 and I vary my photoperiod from 13.5 peak in summer to 11.0 hours in winter. Particularly for the Phals, I think the reason for success in growing and blooming is related to the 40 degree beam angle of my lights. With diffuse light, rather than collimated/vertical, I think that Naoki's 100 would be closer. I run Phrags and Miltoniopsis at about 80 and Cattleyas are 200-300 at the top of the leaves. My daily light integral range for my varying orchid types is the same range as Naoki's. This DLI matches what has been published for the range of Phalaenopsis to Miltoniopsis to Dendrobiums, but these were mostly with natural, diffuse light in a greenhouse.


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terryros

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A typical PAR meter measures light (photons) in the 400-700 nm wavelength range that is most effective at stimulating photosynthesis. Light outside this range may still have some beneficial effect on orchid culture, but focusing on PAR is reasonable for most hobbyists. Most moderately priced ($200-300) PAR meters aren’t perfect, usually with a measurement dip at one end of the range or another, but they get a good assessment of this most important part of light for orchids. I use an Apogee meter that is simple to use and has been reliable for over 3 years. I consider the investment well worth it considering the money invested in my plants, lights, and other cultural supplies and equipment. Getting light correct is often the difference between poor growth with no blooming and attractive leaves with flowers.

These moderately priced meters typically output the PAR measurement as the instantaneous “photon density” in micromoles/meter squared/sec. With outdoor or greenhouse lighting from the sun, the photon density is changing continuously through the day as the sun rises and sets and as clouds or other obstructions appear and disappear. It takes a more sophisticated meter to record all the densities over the course of a day to result in the “daily light integral” (DLI). With steady artificial light it is easier because you just multiply the number of seconds in the day by the measured photon density per sec. A growing number of orchid culture and blooming experiments are reporting DLI as well as the peak PAR.

The following chart lists five different peak PAR densities that might typically be used with artificial lights and gives the DLI achieved with a photoperiod of 13.5 (second column) and 11.0 hours (third column). The peak PAR should probably be measured in the upper half of the leaf zone.

Peak PAR

50 2.4 2.0

100 4.9 4.0

150 7.3 6.0

200 9.7 8.0

250 12.2 9.9

To put these DLI values in perspective with a few published studies, a Dendrobium experiment in a greenhouse in Texas had DLI that varied from 2.0 in the winter to 10.0 in the summer and achieved good growth and blooming. A Miltoniopsis experiment in another location had DLI that varied from 2.0 - 6.0 over the year and a Phalaenopsis blooming experiment used a range of 2.5 - 4.0 over a year for successful growth and flowering. Thus, our typical lower light orchids like Phalaenopsis and Paphiopedilums can be well served with PAR meter readings between 50 -100 and a photoperiod between 11.0 and 13.5 hours per day. Intermediate light examples might be Phragmipediums and Miltoniopsis which should be good at 100, maybe up to 150. Higher light orchids like Cattleyas and some Dendrobiums would then get the 150 - 250 levels, depending on the species. By the numbers, an average of 300 might even be excessive for some higher light orchids.
 

My Green Pets

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I like this forum because I read threads like this and am reminded of how little i know!

Did we stop measuring light in footcandles/lux at some point... ???
 

terryros

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Those can still be measured, but the focus turned to the light that is most effective with photosynthesis, which is PAR. This is measured in the amount of photons of light hitting a square meter every second. A light may have good intensity in terms of footcandles, but a decent portion might be outside the PAR range. If you know that a particular light is producing mostly PAR, then we can make a conversion from footcandles to photon density. Naoki has some nice posts on various aspects of PAR and conversions from footcandles.


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mr. Ra

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I just stumbled upon this article and thought that someone might have use for it.
While DLI is fairly easy to calculate yourself with numerous calculators online, the chart in this blog can save you some hassle and help you see the correlation between time and intensity.
There's also a couple of nice recommendations for some different crops and plants.

https://www.ledtonic.com/blogs/guid...and-your-plants-ppfd-photoperiod-requirements

While this thread is kind of old, I figured that people are still finding it when googling for DLI.
Sorry if I'm bumping it.

Peace!
 
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A typical PAR meter measures light (photons) in the 400-700 nm wavelength range that is most effective at stimulating photosynthesis. Light outside this range may still have some beneficial effect on orchid culture, but focusing on PAR is reasonable for most hobbyists. Most moderately priced ($200-300) PAR meters aren’t perfect, usually with a measurement dip at one end of the range or another, but they get a good assessment of this most important part of light for orchids. I use an Apogee meter that is simple to use and has been reliable for over 3 years. I consider the investment well worth it considering the money invested in my plants, lights, and other cultural supplies and equipment. Getting light correct is often the difference between poor growth with no blooming and attractive leaves with flowers.

These moderately priced meters typically output the PAR measurement as the instantaneous “photon density” in micromoles/meter squared/sec. With outdoor or greenhouse lighting from the sun, the photon density is changing continuously through the day as the sun rises and sets and as clouds or other obstructions appear and disappear. It takes a more sophisticated meter to record all the densities over the course of a day to result in the “daily light integral” (DLI). With steady artificial light it is easier because you just multiply the number of seconds in the day by the measured photon density per sec. A growing number of orchid culture and blooming experiments are reporting DLI as well as the peak PAR.

The following chart lists five different peak PAR densities that might typically be used with artificial lights and gives the DLI achieved with a photoperiod of 13.5 (second column) and 11.0 hours (third column). The peak PAR should probably be measured in the upper half of the leaf zone.

Peak PAR

50 2.4 2.0

100 4.9 4.0

150 7.3 6.0

200 9.7 8.0

250 12.2 9.9

To put these DLI values in perspective with a few published studies, a Dendrobium experiment in a greenhouse in Texas had DLI that varied from 2.0 in the winter to 10.0 in the summer and achieved good growth and blooming. A Miltoniopsis experiment in another location had DLI that varied from 2.0 - 6.0 over the year and a Phalaenopsis blooming experiment used a range of 2.5 - 4.0 over a year for successful growth and flowering. Thus, our typical lower light orchids like Phalaenopsis and Paphiopedilums can be well served with PAR meter readings between 50 -100 and a photoperiod between 11.0 and 13.5 hours per day. Intermediate light examples might be Phragmipediums and Miltoniopsis which should be good at 100, maybe up to 150. Higher light orchids like Cattleyas and some Dendrobiums would then get the 150 - 250 levels, depending on the species. By the numbers, an average of 300 might even be excessive for some higher light orchids.
I have a question about the trade-off of light intensity and duration. I'm growing mostly phals, paphs, and phrags under LEDs. Given the specs from the manufacturer (confirmed, FWIW, by an iPhone app that seems pretty good!), the PAR readings are higher than suggested here. Given the setup, I can't conveniently move the lights higher. But I can keep them on for less time, getting the same DLI as described here. Is that a bad idea? One other note: the paphs have strong leaves, but lots of red, which I've heard can be from too much light.

Rich
 
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It's called Korona. It's at the App Store. There's an add-on for LEDs. And there's a website with some information. I'm no expert, so I can't add to what I said above about its accuracy.

Rich
 

terryros

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There is a maximum amount of photons/light that a plant can take at one time before adverse consequences occur. Compared to sunlight, we are probably less likely to get burning of leaves from high light with LEDs, but the plant may just shut down. Seeing purplish discoloration of leaves may indicate strong light on some plants, but this isn’t necessarily an indicator of excess light. Decreasing day length will decrease the daily light integral for the plant and may help you to a point, but there may be consequences to the short days. For some this may be a triggering of blooming our of season. I think I would worry with days less than 10 hours throughout the year, but you may just have to run your own experiment.
 

Ray

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I’m with Terry on this.

There ere chemical reactions driven by light, and they each have their own kinetics. It takes a fixed amount of time for “this” to be broken down and combined with “that”, and it happens one molecule at a time. The plant relies of “so many” of those reactions to take place during a day, with other reactions happening at night, also with their own kinetics.

Increasing the light intensity does not necessarily speed up that reaction. It may allow more reactions to take place per unit time, but there may be factors that limit the number of reactions that can happen simultaneously, and that would suggest that higher light for a shorter time may not allow the plant to build reserves as well than the right light and duration.

I think phalaenopsis offer a good example of that. Grow them under “short days” with moderate light intensity and they will grow well, but grow them under low light levels for longer periods and the foliage will be far more lush and the flowering will be much better.
 

Ray

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Bits of black electrical tape...
 

southernbelle

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I've taken light-loving multiflorals as high as 400.
I’m wondering what Par meter you are using? The Apogee Quantum 200 accurately measures the LED spectrum (5,000 K daylight) the Quantum100 does not (it under reads the level), and I have to be careful at 300 PAR at top of leaf canopy on high light Cattleyas such as Dowiana, percivilana, L. purpurata, Semontiana and warscewiczii, even though they are recommended to take that light. I can get the beginning of burning if I’m not diligent watching them. My multi-florals are at much lower PAR (closer to 100) and bloom well.
 

terryros

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I think that Debra (Southernbelle) and I are using Apogee Quantum Flux model MQ 500 full spectrum meters for our readings. The photon flux readings are filtered to show only what is coming in the PAR range. The available published information in greenhouse locations gives peak light intensity for Cattleyas and Dendrobiums in the 300-600 micro moles/m2/sec range. This would be summer noon peaks. For indoor continuous light, this would translate to half this amount (150-300) to give the same total light over the same number of day length. A reading of 400 micro moles/m2/sec under LED lights would likely be more than what most higher light orchids would need.
 

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