LED Lighting - Intensity vs Duration/clarity
 

Hello smart people... I've really only grown orchids under LED light panels and have had great results. I've never had a burn and have had success with reflowering most plants that I have attempted.

I use these lights and use a light meter to measure FC.
Robot Check

My catts get 2000-3000 fc under these lights, less than what is listed that they require, yet all new growth is highly pigmented, which in my understanding means they are receiving more than adequate lighting. I've rebloomed most of the catts under these lights.

Finally my question: How do we think about duration and clarity alongside FC? My plants under LEDs never get shaded, never experience a cloudy day, never get burnt despite being exposed to direct light for however long I wish them to be. How much does this compensate for the intensity not being the same as an hour of direct sun in the morning?

DLI (Daily Light Integral) Chart - Understand your plants' PPFD & phot – Ledtonic

what you're describing is DLI. footcandles is an outdated and annoying metric still used in orchid culture guides. I grow many cattleya types at 200-250 ppfd = 1000-1250 fc and they bloom and show pigmentation. i use a photoperiod of 12 hours.

1) Light meters are notoriously bad at measuring the output of LEDs. Unless yours is intended specifically for that application, your readings aren't telling you as much as you may think. Hence the apparently low intensity and pigmentation.

2) When you see a foot-candle recommendation, that is the peak, noontime intensity to which they may be exposed. Under artificial light, the intensity need only be about 50% of that to match the same DLI. READ THIS

I second thefish1337’s comment. Footcandles/lumens/lux measure what human eyes see, and different artificial light sources can result in different intensity levels for photosynthesis even when the fc/lumens/lux values match. A better unit to measure light that plants use is PPF/PPFD, which actually measures the number of photons that drive photosynthesis. The equipments to measure PPF/PPFD are usually more expensive but will yield more reliable results.

Plants have specific DLI (total amount of light received in a day) ranges depending on various factors. Plants that need higher light levels have higher DLI requirements, and vice versa. Artificial lighting will definitely compensate the lack of, if not entirely replacing, natural light in terms of DLI. For cattleyas, this article suggests DLIs from 10 to 15.

Finally, you want to consider photoperiod (number of hours of light exposure in a day). While you can increase photoperiod to make up for the lack of high light intensity, it may be counterproductive and can result in various issues. 12 hours of light a day, which is what growers of medical plants do during the flowering phase, seems to be a safe bet for inducing flowering in other plants.

Hope this helps.

Edit: I was just looking at the link to the LED panel you are using, and the Amazon page actually shows a diagram with PAR levels (in PPF/PPFD) at different hanging heights. Assuming they are accurate-ish, these figures are very useful for you to determine the hanging height and photoperiod for your plants to achieve the desired DLI.

For most orchids, day length (photoperiod) is not critical. 12 on/12 off to as much as 16 on/8 off has worked fine for me. What's key is that the duration x the intensity stay within the preferred DLI range for the particular plant.

There are some cattleya species that rely on short days to trigger flowering, but outside of them, daylength sensitivity is fairly rare.

Thanks everyone, some very interesting learnings from this thread for me, especially about the effect of duration and how to translate the outside light requirement specs into something useful for growing under LED.

I was already familiar with the concept and measurement of PAR and would utilize it if the equipment wasn't cost prohibitive and there was a resource that had orchid species light requirements listed in PAR. Instead I was using FC to approximate PAR while know the spectrum of my grow light. I did not know however that my light meter was no good for measuring LED FC (thanks Ray).

Since I would rather buy more lights and orchids (and pay my mortgage) as opposed to a PAR meter I think I will just let the plants tell me if they are happy. Obviously flowering is the ultimate goal. Am I correct in assuming pigmentation is a good sign the plant is getting the right amount of light and leaf yellowing/browning is a sign of too much?

since you're not noticing any flowering issues I'd say your current conditions are good. burning of leaves from too much photons is at the extreme end of exceeding your plants DLI. pigmentation may not give you the whole story. more light than nessesary increases demand for water, nutrients and co2 to sustain photosynthesis which can make it harder to keep up with your plants and leaves less room for mistakes. why not estimate the par at given heights from the amazon product listing and then use the chart I posted to put your cattleyas in the 10-15 DLI range? maybe they're already right. you know the par your light puts out at various distances and then you can estimate how much DLI your plants are getting from your light cycle. easy peasy

Thanks once again for the guidance and for elaborating on why too much light can be harmful short of leaf burn.