Conflicting PPFD/LUX recommendations

[guccisimo85]

Hello!


I have been perusing a few different sources on light requirements for high light orchids (e.g vandas, cattleyas). I seem to be seeing conflicting information. A few resources suggest around 50k lux / 4500 ftc (which seems correct to me). I know they need lots of light. There is this a popular guideline however on a few threads which seems to be in conflict (see below). My understanding is that 50k lux will be around 1000 PPFD, so 200-300 seems extremely low. Can anyone clarify? Not sure if it has something to do with the units being m2 or ft2? Seems like maybe there is some inconsistency in units and resources are off by a factor of 10?

Thanks!

Light Targets for Orchids

20 umol/ft2 (~65 umol/m2s PPFD) – for low-light orchids (Phals, Paphs, Jewel Orchids)
30-40 umol/ft2 (~131 umol/m2s PPFD) – for moderate-light orchids (Oncid, Phrags, Epidens, Dends etc)
50-100 umol/ft2 (~200-328 umol/m2s PPFD) – for high-light orchids (Cattleya, Vandas)
**Converting feet to meters: 1m = 3.28ft

[camille1585]

With the conversion factor from natural light to PPFD, 50K LUX should be around 1000 PPFD, so that's correct. As to the 200-300 μmol/m²/s , that seems about right to me. I work at an indoor farm company and we can grow tomatoes commercially under LEDs with 250μmol/m²/s, and tomatoes have rather high light requirements.

Most resources seem to base their recommended light levels on the max light a species/genus will receive over the course of the day. If you consider the natural progression of light intensity over the course of a day, the averge value is far lower than that. That's also why it's far better to work with DLI, or Daily Light Integral, which is the cumulative amount of light a plant needs over the course of 24 hours. This is dependent not only on the PPFD, but also photoperiod. If you take my tomato example, this crop needs a DLI of 14-18 mol/m²/d. 16 hours of 250μmol achieves that. Phals have a DLI of about 4, Cattleyas 10-15, Dendrobiums 8-10, at least from what I read last year when doing some research for work.


Don't covert the PFFD units to square feet, it's metric unit and meant to be in m². ;-)

[guccisimo85]

Fantastic explanation! That actually makes a lot of sense since the light intensity will be a lot lower outdoors early and late in the day.

Now you have shown me how to go from PPFD to DLI too, which is something I never thought of before

Originally Posted by camille1585

With the conversion factor from natural light to PPFD, 50K LUX should be around 1000 PPFD, so that's correct. As to the 200-300 μmol/m²/s , that seems about right to me. I work at an indoor farm company and we can grow tomatoes commercially under LEDs with 250μmol/m²/s, and tomatoes have rather high light requirements.

Most resources seem to base their recommended light levels on the max light a species/genus will receive over the course of the day. If you consider the natural progression of light intensity over the course of a day, the averge value is far lower than that. That's also why it's far better to work with DLI, or Daily Light Integral, which is the cumulative amount of light a plant needs over the course of 24 hours. This is dependent not only on the PPFD, but also photoperiod. If you take my tomato example, this crop needs a DLI of 14-18 mol/m²/d. 16 hours of 250μmol achieves that. Phals have a DLI of about 4, Cattleyas 10-15, Dendrobiums 8-10, at least from what I read last year when doing some research for work.


Don't covert the PFFD units to square feet, it's metric unit and meant to be in m². ;-)

[camille1585]

My tomato example should read 300μmol and not 250, but the principle stays the same.

Just curious, what are you looking to do? Will you be growing in a completely enclosed environment with no natural light?

[guccisimo85]

I’m trying to figure out the best way to supplement my orchids. I am getting a couple vandas and since I am in Vancouver, BC - light levels will be low in the cooler months. I have east facing windows - which get consistent 100-150 PPFD, but that will still leave me short on the DLI. I have a floralight unit at the moment which appears to be actually only giving me max 100 PPFD several inches from the bulbs (hadn’t measured it previously).

Thinking maybe I should get one of those tripod LED fixtures they have online so i can keep them at the window all the time with the supplemental light. It’s hard to get output information on them.

What do you think about something like this?

https://www.amazon.ca/gp/aw/d/B083W7...6PAN6FW3&psc=1

Originally Posted by camille1585

My tomato example should read 300μmol and not 250, but the principle stays the same.

Just curious, what are you looking to do? Will you be growing in a completely enclosed environment with no natural light?

[hypostatic]

So I think the confusion comes from the fact that a lot of the light recommendations are fairly subjective and qualitative, instead of being quantitative measurements taken with precision scientific instruments. I believe this is due to the costs of precision instruments, and the fact that the vast majority or growers can get by without them.

As a result, you'll see very few mentions of moles of light per meter squared, and that most recommendations AREN'T in Lux -- they are instead in footcandles. I've grown to prefer FC as a measurement, because I think it makes more sense intuitively: full sunlight at the equator is about 10,000 FC; 50% shade at the equator would then be 5,000 FC. In my opinion, it just makes nicer number to work with. (whereas full sunlight at noon at the equator would be 109,791.89 lux)

---------- Post added at 02:23 PM ---------- Previous post was at 02:19 PM ----------

Originally Posted by guccisimo85

What do you think about something like this?

Robot Check

Oh, and personally, I would recommend against the red/blue LEDs. I think the purple/magenta hue that they make everything is unpleasant. I'd go for something that is in the 5500-6500 Kelvin color