# How much PAR are your orchids getting?



## ChrisFL (Sep 15, 2017)

Give me a daylight average or the mean for your lighting system.


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## troy (Sep 15, 2017)

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


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## naoki (Sep 15, 2017)

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.


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## terryros (Sep 15, 2017)

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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## ChrisFL (Sep 15, 2017)

Thank you!!! These are exactly the types of numbers I was hoping to see.


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## terryros (Sep 15, 2017)

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.


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## Ray (Sep 16, 2017)

Nice explanation, Terry.


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## My Green Pets (Sep 17, 2017)

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... ???


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## terryros (Sep 17, 2017)

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 (Jun 5, 2019)

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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## richard.feldman48 (Oct 16, 2020)

terryros said:


> 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.
> 
> ...



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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## Silverwhisp (Oct 16, 2020)

Rich, out of curiosity, which iPhone app do you have?

Thanks-


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## richard.feldman48 (Oct 16, 2020)

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


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## terryros (Oct 16, 2020)

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.


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## tnyr5 (Oct 16, 2020)

I've taken light-loving multiflorals as high as 400.


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## Ray (Oct 17, 2020)

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.


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## richard.feldman48 (Oct 17, 2020)

Thanks for the advice. I'll find a way to reduce the intensity to better levels. 

Rich


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## Ray (Oct 17, 2020)

Bits of black electrical tape...


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## southernbelle (Oct 17, 2020)

tnyr5 said:


> 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.


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## terryros (Oct 19, 2020)

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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## southernbelle (Oct 19, 2020)

terryros said:


> 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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## terryros (Oct 20, 2020)

And, you are getting what kind of readings for peak photon flux at that location?


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## southernbelle (Oct 21, 2020)

terryros said:


> And, you are getting what kind of readings for peak photon flux at that location?


250 PAR at top of leaf canopy. It’s obviously happy, growing well and a first bloom spike with 5 buds about a week from opening.


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## Geek_it (Oct 29, 2020)

Ray said:


> 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


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## Ray (Oct 30, 2020)

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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## Elite Orchids (Oct 30, 2020)

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 (Oct 31, 2020)

What unit is the meter displaying?


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## Elite Orchids (Oct 31, 2020)

Ray said:


> What unit is the meter displaying?


14 PAR i believe


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## Ray (Oct 31, 2020)

"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.


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## southernbelle (Oct 31, 2020)

Elite Orchids said:


> 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.


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## terryros (Oct 31, 2020)

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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## Elite Orchids (Nov 1, 2020)

our meter is the MQ- 500 from apogee - i can't see any where to change the measuring units - per second or per day.


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## terryros (Nov 1, 2020)

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.


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## Ray (Nov 1, 2020)

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


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## terryros (Nov 1, 2020)

Yup- don’t know why I did that. Micromoles/m2/sec


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## Elite Orchids (Nov 2, 2020)

terryros said:


> Yup- don’t know why I did that. Micromoles/m2/sec


how does that affect your calculations?? is my light source too low??


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## terryros (Nov 2, 2020)

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.


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## Elite Orchids (Nov 12, 2020)

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 (Nov 12, 2020)

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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## Elite Orchids (Nov 13, 2020)

terryros said:


> 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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## masaccio (Dec 14, 2020)

Ray said:


> Bits of black electrical tape...


I'm trying to picture this for my spot lights. Not full strips from side to side, but like several little squares until I get the reduction I want?


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## Ray (Dec 15, 2020)

Either one.


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## podiver (Jan 3, 2021)

This has been an incredibly interesting thread. I admit to going down the rabbit hole trying to understand light from LED's. I am conversant in PAR, PPFD and DLI now. Your measurements of PPFD and suggestions for DLI for different species are a great starting point. You have not commented on reflected light from light or dark surfaces other than to state that this light penetrates the canopy and that the increased distance from the wall to plant will reduce the intensity (1/d2), and I suppose would be added to the PPFD/DLI from your source. Is there any suggestions as to the amount of increase with a manufactured supplied PPFD at a known distance? And how do linear light movers play into this? (my integral calculations are a little too far in the past) Purchasing a 'PAR' meter would probably answer that question in my circumstance, but I am curious if anyone has any experience with these variables.


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## Ray (Jan 4, 2021)

@podiver Great question, but I doubt it can be accurately answered without having a meter!

The inverse-square rule applies easily to a point light source, but when you have many “points” of emission, the reinforcement calculation becomes more and more complex. Just think about each particle of phosphor as a point emitter on each of multiple, “white” LED chips, each at a slightly different distance from the “receptor”, and each at a slightly different distance and angle from a reflective wall. Then add to that the potential reflective variables of that wall - how truly flat it is, how much is absorbed and re-emitted versus reflected or absorbed, what is the sum of the intensities of the multitude of point sources hitting any single spot, plus the variables in their intensities.

I like math, but I’m not going anywhere near that calculation!


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## paphiopere (Jan 19, 2021)

Loco, he estado leyendo tus comentarios. Un mundo nuevo que acabo de descubrir. sere cuidadoso


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## Russ1992 (Feb 21, 2022)

Geek_it said:


> 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 I don't want to speak for Ray but he has answered this question on Orchidboard.com You can find his specific explanation here: LED Lighting - Intensity vs Duration/clarity - Orchid Board - Most Complete Orchid Forum on the web ! and a great article written by him here: Light Level Recommendations › First Rays LLC


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