How much PAR are your orchids getting?

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ST Supporter
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Jan 16, 2019
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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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Nov 28, 2019
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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.


Orchid Iconoclast
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Jun 9, 2006
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Oak Island NC
@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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