LED lights and PAR w/ Paphs&Phrags

Discussion in 'Slipper Orchid Culture' started by shade131, Feb 7, 2019.

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  1. Apr 1, 2019 #81

    masaccio

    masaccio

    masaccio

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    I totally trust your experience and am relying on it. I'm not suggesting I would use the MR16s for cattleyas (ideally). I've actually already replaced the MR16s that were over my cattleyas with my old 2650 lumen spots for the time being. The spectrum isn't the best but a bit of natural light is helping. HOWEVER ;), the question still remains of rectifying these MR16s with the distance recommendations posted for these lights. Jerry insists repeatedly, against my stubborn skepticism, that these bulbs are effective at surprising distances. I trust him. I just don't understand it and it will bug me until I do.

    LEDs register convincingly on a foot-candle meter. When I measure my MR16s with a footcandle meter at 32 inches, I get a reading of about 1500 directly under the bulb. Tagging onto comments Ray has made about downwardly adjusting plant light intensity requirements when converting from natural to artificial light, a constant supply of 1500fc under artificial light for 12 hours every day would theoretically suffice for a plant rated as needing 3000fc of natural daylight. So, maybe the specifications posted for these MR16s are based on footcandle readings and are assuming a constant supply of this light for 12 hours per day making up the other 1500fc. Maybe even extending the time a little bit but I don't think this is recommended.

    So, I have a measly 35 micromoles/m2/s at a distance of 32 inches from these bulbs. When I measure natural light at 3000fc, and then measure that same 3000fc with a PPFD meter, I receive a yield of about 70 micromoles/m2/s. Measuring directly under the MR16 with a footcandle meter at a distance of 32" registers about 1500fc (half the first reading under natural light). Measuring the same distance with a PPFD meter yields about 35 micromoles/m2/s as stated. So it seems that the proportion of micromoles/m2/s to footcandles at varying intensities remains constant and also applies to both natural light and artificial light of comparable quality. So given that the proposal is grow plants under artificial light yielding 35 micromoles/m2/s (or 1500fc) at a constant exposure of 12 hours every day, is it arguable that the MR16s would, after all, suit orchids requiring 70 micromoles/m2/s (or 3000fc) in natural light?
     
    Last edited: Apr 1, 2019
  2. Apr 1, 2019 #82

    masaccio

    masaccio

    masaccio

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    That last dubious statement of mine of course doesn't hold. Disappointlngly, the statement "micromoles/ms/s" is not directly correlated with footcandles. According to this theory for terryros to achieve his 200-400 micromoles/ms/s he would have to be applying more than 10,000 fc. Denial is a wonderful thing. But the general theory holds, that constant application of low light level compensates for plant ratings that are based the ebb and flow of natural light. It still seems apparent that the MR16 specifications are based on footcandles, not micromoles/ms/s. They stated that, as with all things orchids, improvement from using these bulbs would not be dramatic, but would be noticeable over a period of a few months. I can't fool around with cattleyas this time of year, which are either blooming, or are setting up put on new growth. I'm getting those micromoles AND footcandles one way or the other. I'm sure the elusive answer combines quantity as well as quality for higher energy plants.
     
  3. Apr 2, 2019 #83

    terryros

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    I use an Apogee Quantum meter. I don’t think there is an easy conversion from foot candles to the micromoles/m2/sec output from the meter and I don’t try to do this. The Apogee website implies, but isn’t certain, that the peak photon flux being measured is predominantly in the PAR frequency range. A footcandle meter would most likely not be doing this.

    I need to be about 20 inches directly underneath an ALT MR16 7 watt true white bulb labeled as 720 lumens to get 50 micromoles/m2/sec. My Phalaenopsis grow and bloom well at or below this intensity. I give daylight varying from a peak of 13.5 hours in the summer and 11.0 hours in the winter. I grow and bloom Phrags under these bulbs with photon density of 60-80 micromoles/m2/sec. Daily light integrals for my Phals would range from about 2.0-2.4 per day (units omitted). These are very far away from anything published as adequate for high light orchids like Cattleyas. I use ALT 15 or 20 watt, 60 degree bulbs for my Cattleyas giving me peak photon flux at the top of the leaves of 300-400 and daily light integrals between 10-14.

    I have to admit that I have never, in the 8 years that I have been using the MR16s, attempted to use them to grow Cattleyas! So, I can’t prove that they wouldn’t get the job done! Perhaps I am giving Cattleyas excessive light, but I do not have leaf signs to indicate this. I will continue to think that the MR16 are great bulbs for lower light orchids that need great head room over the plants to accommodate spikes.
     
  4. Apr 2, 2019 #84

    Ray

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    The "5 factor" comes from Apogee's website. Full, noontime sun is about 10,800 fc and 2000 µmol/m2/sec. It's a "crap estimate" comparing apparent brightness to actual photon density, but it's all we have for translating form culture guides.

    They show graphs of the spectral sensitivity of their quantum sensors, so I don't under stand the uncertainty comment.

    There are a few aspects of light measurement that makes it difficult to translate from one scale to another, not to mention one light meter to another.

    When we see a lamp labeled as "X lumens (or lux)" output, it is the apparent brightness of the lamp, that is, how bright it appears to the human eye, right at the surface of the bulb. As we move farther from the bulb, it looks less bright (and is) due to the "spreading out" of the photons, which holds true for any light measurement. PLUS - the spectrum also plays a role, as the human eye is most sensitive in the green portion of the spectrum. If we have two "white" lamps with identical photon outputs, but one has more green in its spectrum, it will appear brighter. Most light meters are designed to match human perception.

    When we start talking photon flux, µmol/second, lamp comparison is linear - differences are literal, not apparent. The flux density, moreover, also decreases with distance due to photon "spread". A point light source - ANY light source - radiating in all directions, exhibits the same inverse-square relationship in light intensity (or density, if you will). Physical design and reflectors, however, can certainly affect that. Working backwards from Terry's measurement, 50 µmol/m2/sec x 5 = 250 foot-candles using the Apogee factor, and considering the directionality of the lamps, that's not out of the realm of possibility at all.

    Quantum meters for plant light measurement merely have the measured portion of the spectrum limited by filters, and are linear in that range, i.e., not enhanced sensitivity for green wavelengths.
     
  5. Apr 2, 2019 #85

    Silverwhisp

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    Although I don’t have a meter - yet - it might be helpful to others to View attachment 15039 know distance from bulb to plant leaf. E.g., in my case, although the vertical shelf spacing is 30”, the MR 16’s are 11” from Phrag. Frank Smith.

    I think it’s working:
    upload_2019-4-2_9-27-49.jpeg
     
  6. Apr 2, 2019 #86

    masaccio

    masaccio

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    This make sense. I may be getting a little bit of a feel for this. The problem now facing me is that I've ordered track lighting for an 11 foot long, 12" deep orchid "shelf" setup in another room. It will be a paph garden, and perhaps a few other plants that are light compatible. I absolutely need enough light for the higher light polyanthas -- philippinense and the like. So the light will have to be securely medium in intensity - not just the low medium that one usually thinks of for paphs. Perhaps your phrags also fall into this somewhat higher light category.

    The track and fixtures ordered are line voltage, and the fixtures are just the sockets so I can substitute out normal household bulbs freely. Based on recommendations, I was planning on using 30 degree MR16s for these plants. If I mount the track directly overhead, the fixtures will be approximately four feet above the plants, or slightly less. I wanted to pull the track out a little bit so the plants receive some side lighting as well. This might add 6-8 inches distance. I'm beginning to feel that using MR16s for this setup, even the 30 degree, is wishful thinking. My gut impulse at this point is to use 2650 lumen spots at 5000K. If they're a little too bright, and they may not be, I could dim them down a little.

    Orchids Limited is stgrongly recommending the 30 degree MR16s, and naturally I respect the opinions offered but am having a failure of confidence in these bulbs at the distance I am proposing. Any insights, recommendations would be greatly appreciated. The track will be installed in a few days; I have to decide whether I have to mount directly overhead or whether I can afford to pull the track out a little. I guess the bulbs can be selected a little later.
     
    Last edited: Apr 2, 2019
  7. Apr 2, 2019 #87

    Ray

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    If Terry measured 50µmoles/m2/sec at 20", then you can expect no more than 12 or so at 40", and less at 48" or more. Realize, however, that if you increase the number of lamps, you increase that. Four of them aimed at the same area from 40" would give the same PPFD that Terry measured for one at 20".
     
  8. Apr 3, 2019 #88

    shade131

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    That doesnt sound like enough light at all. You'll need around 150 for medium light - very rough estimate.
     
  9. Apr 3, 2019 #89

    masaccio

    masaccio

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    Well, I've heard it over and over again, now. I guess it's time for Plan B. Thinking to mount the track on a rear wall, a bit farther down, instead of on the ceiling. Will have to figure out a way to bring it out a bit so the bulbs are over the plants. I wouldn't mind a little side lighting in theory, but if I did this from the rear wall, the bulbs would be pointing into the room. Not good. I also could do the same arrangement I have in my first setup - with spots hanging from a curtain rod. The adjustability is great, but not a very clean look, with all the wires. Thanks for the responses.
     
  10. Apr 3, 2019 #90

    masaccio

    masaccio

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    Interesting. I took a series of comparison readings with both a foot candle meter and my PAR meter through a northeast window early this afternoon. Perfectly clear day, stable light conditions. Foot-candle meter registerd 2250fc. The PAR meter measured 23 μmols/m2/s. I chose a placement and angle that I could reasonably duplicate with both instruments and took several readings. Not being a light expert, I guess it's possible that this may have no meaning whatever. But if midday light at 2250fc also delivers 23 μmols/m2/s then it seems to stand to reason that this PPFD level is satisfactory to grow many medium-low light orchids.
     
  11. Apr 3, 2019 #91

    Ray

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    I think there must be a significant discrepancy in the light capture of the two meters. Full, noontime, summer sun is 10,800fc and 2000 µmol/m2/sec. The fc meter shows close to 20% of that while the PAR meter is closer to 1%.

    Sump'n juss ain't raht.
     
  12. Apr 3, 2019 #92

    terryros

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    Ray, the Apogee material shows the sensitivity of the meter in the PAR range, but I wasn’t sure that this means the meter is only measuring photons within this range when it is reporting the output. I have always hoped this was the case, but saw how I could interpret it correctly. My Apogee meter has a setting for “electric” and a setting for natural light. I am not quite sure how this works either, but I think the variation in how footcandle and photon flux meters compare may have to do with the filters and settings for electric and natural light.

    I have 7 MR16, 7 watt. 40 degree bulbs covering a 4 foot length of humidity trays. By geometry, I calculate that the height I am using covers about a 24 inch wide swatch down the trays. The intensity is highest at the center and under each light, but the overlap of the beams gives acceptable light to most of the leaves.
     
  13. Apr 4, 2019 #93

    masaccio

    masaccio

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    No idea. For the sake of argument, let's say that my meters are in the ballpark. Any other explanation for direct sun to have a higher rate of PPF than ambient light?
     
  14. Apr 4, 2019 #94

    naoki

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    It is measuring the range indicated by the sensitivity curve. However, since the older Apogee didn't have a flat sensitivity curve, the spectra of light influence the reading. The error is largest when the light contains lots of deep red. So they have calibration coefficients for sun and artifical light (electric). With the newer Apogee (500 series), the response is fairly flat, and pretty similar to Li-Cor Quantum sensors. So they don't have to have the different coefficients.

    Indeed, if you know the spectra, you can make the exact conversion coefficient. Apogee has some info here: https://www.apogeeinstruments.com/how-to-correct-for-spectral-errors-of-popular-light-sources/ But for the practical use, you don't have to worry about it. Bulk Reef Supply has a video (link) comparing the practical differences between old and new Apogee and LiCor. They use blue heavy light (for reef aquarium), but the cheap old Apogee is good enough.

    Indeed, if you can get the sensitivity curve of cheap lux meter (and know the emission spectrum of the light), you can calculate the exact conversion factor to convert lux (or fc) to ppfd. But unfortunately, cheap lux meters don't provide the sensitivity information. Also they can deviate quite a bit from the standard luminosity function.

    Massaccio, one of your meters are apparently broken or completely out of calibration. I would guess fc meter if you are measuring next to north facing window. Even if you have accidentally set it at lux instead of fc, it is still quite a bit off. With indirect light, the spectrum can be shifted compared to direct light, but you will not see that much deviation.
     
    Last edited: Apr 4, 2019
  15. Apr 6, 2019 #95

    spujr

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    I've been following this thread with interest because it is a subject I would (should) like to know more about.

    I have a lumens reader (lux/FC) and made measurements around my growth area. For the most part, where my paphs are I am at 300-400fc, depending obviously where it is situated and how far away from the light. This reader was pretty consistent with the FC App reader one can get on their phone.

    I thought these readings were low because I read in various places that paphs like armeniacums like around 1500fc.

    Well the plants don't seem to mind my conditions, all leaves are light green including the higher light requirement species like Cats, Neos (now vanda), and dendrchilumns.

    I'm using a full spectrum ~300w quantum dot led, placed about 6ft up as my main source. I added 4, 13.5w strip leds to add light on the edge of the growth chamber. However, being placed 6ft high I don't think they contribute to much and planning to put them on a shelf system in another area in the future.

    Apparently one gets more "bang for the buck" by using the 13.5w leds than the 300w one I got, where the 13.5ws only cost ~$30 apiece versus ~$800 for the other. However they would need to be placed closer to the plants. As for me, I got both for a cheap price through work so using what is given. 0406190942a.jpg 0406190942a.jpg
     

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  16. Apr 8, 2019 #96

    southernbelle

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    How is your bloom? That would be the greater test than growth, I would think.
     
  17. Apr 11, 2019 #97

    masaccio

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    I believe I stated a northeast window. I also have a digital fc meter that confirms the analog silicon sensor fc meter I was using. Taking another reading today, 2:00pm EDST, overcast day from inside, pointed at the sky next to a single-paned window. Getting readings from both meters in the 4500 4750 range. PAR meter is giving me 260 micromoles/m2/s. What say you? Thanks.
     
  18. Apr 11, 2019 #98

    naoki

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    Then your PAR meter is broken. I'm assuming that you are using the same window, you had 2250fc and 23micromol/m^2/s earlier. Now you have 4500fc and 260 micromoles/m^2/s. 2x difference in fc, but 12x difference in PPFD. What kind of PAR meter are you using?

    Why don't you measure outside under direct sun when there is no cloud? You can calculate the expected PPFD using this calculator:

    http://clearskycalculator.com/quantumsensor.htm

    You can multiplied the calculated value by 5.01 to get the expected fc.
     
  19. Apr 11, 2019 #99

    masaccio

    masaccio

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    I see what you mean. Just found the Apogee website that has conversion tables. I'm heading outside. Thanks.
     
    Last edited: Apr 11, 2019

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