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How much PAR are your orchids getting?

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southernbelle

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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.
Terry, I stand corrected and thank you. Of course, you are right, my Quantum Flux is the MQ 500 not the 200. I mis-spoke. By the way, the very tall Lc. ‘Aphrodite’ that we spoke about today is under 3 tubes 20” above leaf canopy.
 

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Bits of black electrical tape...
Hi ray, just to confirm, your suggestion for phals is lower intensity for longer period?

can you elaborate on period? Do you mean shorter days = less than 12 hrs light? What if its constant 12hrartificial light?

TIA
ace
 

Ray

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What I was trying to convey in that last paragraph is that many phals are near-equatorial in origin, so get long days naturally. Plus they are deep understory plants, so live in deep shade. When we grow them in shorter-day environments and expose them to more light, they may be getting the equivalent DLI, but it puts them at a physiological disadvantage.

If, on the other hand, we continue to grow them at lower light levels (and are tolerant of the time it takes them to adjust to that), once they have adjusted, they will bloom much better.
 

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interesting thread - we have some under bench growing areas we illuminate with simple led strips - we get a reading of around 14 PAR, but we get good growth on most paphs. to me this sounds to low a figure, has anyone got any experience of this? thanks
 

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Ray

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What unit is the meter displaying?
 

Ray

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"PAR" means "photosynthetically active radiation" - it describes a range of wavelengths within the spectrum, not an intensity, and has no units.

I was looking on a tablet earlier, but on my PC I can blow the second picture up enough to see it is the photon flux - meaning your display is showing 14 µmol/square meter/second.

So... 14 x 3600 = 50,400 µmol or about 0.05 moles per hour (per square meter), so if your lights were at that intensity for 14 hours per day, your plants would be getting a DLI of 0.05 x 14 = 0.7 which is VERY low.
 

southernbelle

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interesting thread - we have some under bench growing areas we illuminate with simple led strips - we get a reading of around 14 PAR, but we get good growth on most paphs. to me this sounds to low a figure, has anyone got any experience of this? thanks
I can’t see which Apogee Meter you are using, but I had a MQ 100 and it was not full spectrum for LEDs and under read the levels by close to 20%. terryros can give you better specifics. He rented a MQ510 after suspecting something was askew, and after seeing the discrepancies, he and I went with the MQ 510 and now know truly what levels we are getting.
 

terryros

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My Phals grow and bloom well with 50-70 micro moles/m2/sec and I use day lengths varying from 13.5 to 11.0 hours throughout the year, which be as much variation as any Phal receives in the natural environment. This is measured with the new Apogee full spectrum meter. The small amount of published information indicates that Phals do well with as little as 4 for a daily light integral and I suspect that they could grow acceptably with a little less light but I don’t think a DLI of 1 would be enough.
 

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That is the full spectrum meter and it only measures photons in millimoles/square meters/second. That is the most commonly used units for expressing the instantaneous measured light intensity in the PAR range (400-700 nanometers of wavelength).

To get to DLI (daily light integral) you multiply this by the number of seconds in a day. Data from the natural light world (mostly greenhouse) showed Dendrobiums grown successfully in Texas with a DLI varying from 2 in the winter to 10 in the summer. Miltoniopsis varied in another experiment from 2-6 and Phalaenopsis from 2.5-4.0. So, I think of higher light orchids being successful in the 10-14 DLI range and lower light orchids in the 2-6 range. There is obviously an intermediate range for some things.

The advantage of calculating your DLI is that day length matters. A green house in northern climates could have day lengths varying from 9 hours to 15 hours without any artificial light, and yet the light intensity would also vary a lot as the sun angle changes throughout the year. This is radically different from the natural environments of most of the orchids we grow. Many orchids have photoperiod clocks so they can respond to even subtle changes in day length. Using a lower light intensity but excessive day length can get to a target DLI number, but some orchids will respond sub optimally because of the extreme day length.

Greenhouse owners in northern climates are stuck with day lengths of 15 hours in the summer but the light intensity in early morning and later afternoon falls off, so the DLI does not become excessive. Yet, some orchids can "stall out" in mid summer and then pick up again in early fall when day length (and maybe temperature) is more in their comfort zone. An indoor artificial light grower can have more precise control of day length, light intensity, and temperature. I run my room with day lengths varying from a low of 11.0 hours in mid-winter to a high of 13.5 hours in mid-summer. My low light orchids get peak photon flux density (PPFD) in the PAR range of 50-70, some intermediate things (Phrags) get 80-110, and my Cattleya group stuff get 150-300 peaks. I vary the light intensity only modestly through the year because that is what happens naturally. That gives me my target DLI range for the groups throughout the year.
 

Ray

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Terry - blow up that middle photo. It says micro-, not millimoles.
 
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terryros

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By your picture, you are matching my MQ-500 Apogee meter and not my MQ-100, so you appear to have a full spectrum meter. You shouldn't be under-measuring the intensity of light in the PAR range. I mistakenly used the incorrect units my post above - the meter correctly displays micro moles/m2/sec. However, your screen is showing LOG. Use the mode button and on about the first screen you will see SMPL and LOG -yours will show the LOG flashing. Use the up arrow to switch to SMPL and then keep hitting the mode button to get back to the home screen. This will give you the instantaneous peak photon flux density as soon as you turn the meter on. I am pasting below a table that anyone could make but it shows the day length range that I use with the range of light intensity that I find useful and then the associated daily light integral. Again, DLI values up to about 6 are for lower light plants, values 9+ are higher light plants.

1604337844967.png
 

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thanks - here are some readings in "sample" mode . 16 - 22 micro moles/m2/sec is the readings under the benches in various places.

seems very low for paphs.

anybody else got any ideas? currently we run them for about 18 hours a day, which may account for the amount of growth we get on such a low level of light.

what is the calculation for the total photons over an 18 hour period.

thanks
 

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terryros

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There are 3600 seconds/hour. Multiply this times the number of hours to get total seconds of light in the day. With 18 hours you get 64,800.

Multiply this times your instantaneous photon flux, but this needs to be converted to Moles/m2/sec, so 22 from your meter becomes 0.000022

Multiply that times the number of seconds and you get 1.4 moles/m2/day, which is the daily light interval. This could be just enough for a low light orchid and if it wasn't very concerned with photoperiod, it might bloom. Lowering the lights just a bit to get to 30 micromoles/m2/sec would get you to 1.94 DLI and you might get modestly better growth.
 

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There are 3600 seconds/hour. Multiply this times the number of hours to get total seconds of light in the day. With 18 hours you get 64,800.

Multiply this times your instantaneous photon flux, but this needs to be converted to Moles/m2/sec, so 22 from your meter becomes 0.000022

Multiply that times the number of seconds and you get 1.4 moles/m2/day, which is the daily light interval. This could be just enough for a low light orchid and if it wasn't very concerned with photoperiod, it might bloom. Lowering the lights just a bit to get to 30 micromoles/m2/sec would get you to 1.94 DLI and you might get modestly better growth.
thank you so much for your patience - much appreciated. my concolor's are doing really really well under this light (flask to flowering in 2 years) . i will adjust any multi's accordingly. thanks for explaining everything. mark
 
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