Growing Cattleyas under PAR38

[ALToronto]

Jim, I don't disagree with what you're saying about the red/blue lights. Yes, they work well for plants. My point, though, is that the full spectrum LEDs also provide the same red (660) and blue (450) nm wavelengths, along with the rest of the spectrum. So the only advantage of limited spectrum lights is energy efficiency - they will provide the needed wavelengths with a much lower power light fixture.

Here are typical spectral profiles of cool white (top) and warm white LEDs.





Note that the 450 nm peak (blue, same wavelength as in specialty lights) is significant in both cool and warm white variants. The warm white also provides a substantial amount of PPFD at 660+ nm. The presence of the blue peak in warm white LEDs is why some growers don't bother with two different colour temperatures and use only the warm whites.

The reason pot growers have embraced the limited spectrum lights is because their grow houses are identified by their energy consumption. So achieving growth for the least amount of power is very desirable for them, and they will gladly buy these very expensive fixtures if they will help them avoid detection.

Personally, I'd rather waste a few kWh on the 'unnecessary' portion of the spectrum and enjoy looking at my orchids.

[This Side of Paradise]

I think scale It's something to be considered. If you grow a few plants under a couple low wattage lights a few watts here and there is relatively unimportant. However if you have a large operation a small percent reduction can quickly add up, my plant room has approx 2000 watts going thru so approx any improvement is significant savings

[naoki]

Originally Posted by terryros

Naoki, my four ALT PAR 38 Astoria 30 Watt, 100 degree beam angle, 4000k bulbs are listed on the box/bulbs as 2480 lumens.

These are not as efficient as their MR16 7 watt, 40 degree beam angle, natural white bulbs at 650 lumens, but this bulb is better for me at a height of at least 30 inches to illuminate lower light plants with higher spikes. The PAR 38 30 degree seem to work the best to cover the same circle of growing area with high light plants.

Oops, you are right! It is 2480lm to give 82.7lm/W, which is pretty good for PAR38! Yes, the MR16 is quite high for a light bulb (92lm/W), even though it is extremely expensive per watt or per lumen. Maybe the heat management is easier with smaller wattage of MR16.

As Jim says lumen/watt is not the best index for plants, but most companies (even the grow light makers) don't publish micromol/J of PAR (BML is good with this regard). I measured PPFD/footcandle ratio of several LEDs and florescent light bulbs. There are some differences, but if you are comparing the 3000K LED bulb to another 3000K LED bulb, the variation in the ratio isn't huge. So lumen and foot-candle can be used as a proxy for efficiency. Obviously lumen or footcandle is no use if we are talking about RB grow light or comparing fluorescent vs LED.

Alla, phosphor technology is super important (as important as progress in emitter efficiency) in the progress of LED, so each company use quite different phosphor technology. The end results may produce similar emission spectra, but the efficiency can be quite different. Indeed Bridgelux Vero V.2.0, which is becoming available now/soon, seems to be using different phosphor than the earlier version from 2014 (the shape of emission spectra changed a little bit compared to the earlier version).

Also, from my experience in measurement of some of the cheaper LEDs, I wouldn't put too much trust on the values published in the Alibaba, AliExpress, or eBay. For example, some 5730 bulbs advertised for 10 or 12W is actually consuming only 2-3W, and they claim 1100lumen or more, but it is extremely dim.

Jim, also don't confuse the absorption spectra of chlorophyll with the action spectra of photosynthesis (I think you probably know this).

If money is no object, I would agree with Jim that my primary interest is the efficiency, so well designed red-blue (with multiple bands) is what I would get. But the technology of white LED has been progressing faster than monochromatic emitters. So PAR efficiency of white LED isn't so bad. Indeed, in one paper, white-red grow light was almost as efficient as red-blue growlight now. I posted the link here. The second and 3rd links are relevant.

I agree with This side of Paradise, the small efficiency doesn't matter much for small scale grow, but it makes a huge difference once you have to cover a moderate size grow area. With 13 hours per day with 1000W, it would cost $830 per year in alaska (with 17.5 cents /kWh, which is expensive end).

[ALToronto]

Naoki, I think we're discussing different points about phosphors. I looked at a lot of spectral graphs of different LEDs before I bought the diodes a year ago. For 6500K, they all looked pretty much the same, just as 3200K lights from different manufacturers had almost identical spectral profiles.

Of course, when you start looking at special, pinpoint wavelength LEDs, phosphor recipes are specific and very proprietary. And I'm not as 'plugged into' (sorry, couldn't resist) the latest research as you are, but I'd be very surprised if there were no innovation in phosphors for consumer lights. I'm talking about more common, currently available lights of the same colour temperature.

I also agree with This Side of Paradise, but this discussion was started by a windowsill grower. All commercial growers, whether pot or orchid, need to be energy efficient. Still, even if I were a commercial grower, I would want to see my plants in proper, white light. Too much information is lost when you cannot see the leaf colour.