Brightness with LED Lights

[naoki]

Samfish, do you have the emission spectrum of your light? Or do you have details of which brand/models of LEDs are used at what proportion? If so, you can calculate the conversion factor (between lux/fc and PPFD). I learned it from this thread:
Math behind | Rollitup
It took for a while to figure it out, but it is pretty cool once you learn it. If you have the figure of emission spectrum (e.g. in forms of spectrum power distribution, SPD), you can digitize it with something like this:
WebPlotDigitizer - Extract data from plots, images, and maps

I think someone or I posted about a cheap USB PAR sensor from BioTek Marine (based on Apogee sensor), but now Apogee released their own.

SQ-420 Smart Quantum Sensor | USB Output - Apogee Instruments, Inc.

$195, and the cool thing about it is that it can log over time intervals. The logging is irrelevant for artificial light, but it is useful for greenhouse growers to get the daily PAR (called Day Light Integrals, DLI).

But as Terry mentioned, Apogee would underestimate deep red (680nm). But if the emission spectrum is known, the correction factor can be calculated for anything (including 680nm LEDs) in the similar method as the Rollitup post I linked.

As Terry mentioned, with constant light, you can get away with fairly low light. Just put it into a context, 500fc of sun light contains 100 micromol/m^2/s. I use a bit more than Terry, though. I've been doing 100-150 micro mol/m^2/s, 13h/day (for Paph/Phal). Maybe I can go even lower. How long is your day length, Terry?

[samfish]

Thanks for the replies, Terry and Naoki!

I currently have one ALT PAR38 30-Watt 100 Degree Light from Jerry at orchidweb.com, and several of the 13-Watt LED Lamps from Ray at firstrays.com

orchidweb.com says the 30-Watt 100 Degree light gives Medium-High intensity at 3-4 feet, and Ray says his lamps grow phalaenopsis well at 12-15" distance... I am trying to quantify intensity, so I can optimize a variety of plants in a relatively small growing area...

I couldnt find much detailed info on spectrum of either light, but will take a look at the site you mention!

Thanks for the info!
-sam

[terryros]

Because some of my orchids are day length sensitive, I vary my daylength from a winter period low of 11 hours up to 13.5 hours for a "summer" stretch. If you do the total daily light integral for these hours and my photon density, you probably come up on the low side, and yet the plants grow well.

I think there is something to the "verticality" of the light my plants receive from the lenses of my bulbs, particularly the 40 degree MR16. Most of my Phals have been producing more compact and round leaves under these conditions and yet still flowering well. I found one study that thought that leaves receiving vertical streams of photons, instead of diffused light, behaved differently.

We still have many things to learn about LED lighting.


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[naoki]

Originally Posted by samfish

Thanks for the replies, Terry and Naoki!

I currently have one ALT PAR38 30-Watt 100 Degree Light from Jerry at orchidweb.com, and several of the 13-Watt LED Lamps from Ray at firstrays.com

orchidweb.com says the 30-Watt 100 Degree light gives Medium-High intensity at 3-4 feet, and Ray says his lamps grow phalaenopsis well at 12-15" distance... I am trying to quantify intensity, so I can optimize a variety of plants in a relatively small growing area...

I couldnt find much detailed info on spectrum of either light, but will take a look at the site you mention!

Thanks for the info!
-sam

If it is mostly white, you can just go with the fc/lux, right?

If you want to know the PPFD, here is a conversion factor of white LED:

0.1514886 micromol/m^2/s per 1 foot-candle.

I calculated this from Cree 4000K 80CRI. There are some variation due to color temp and CRI, but 0.15 is probably good enough. So if your meter says 1000fc, you are getting about 151 micromol/m^2/s. The conversion factor is similar to fluorescent light (see this). Aeon Lighting (ALT) could be using Cree, Bridgelux, Oslam, or Philips, but I didn't see the specification in orchidweb site.

By the way, it has only 82.7 lm/W, which isn't efficient with the current standard. I'm not saying that it is not useful, it will grow plants and some people may not care about efficiency. But you can get LED shop light or T8LED at the fraction of the cost from Walmart or CostCo, which has 98-105lm/W or more. So if you need more (or if you need to replace it in the future), you might want to explore other options.

Ray's have a bit of additional red, so the conversion factor could be slightly different. If I get a chance, I can measure the PPFD and fc. Ray's site says that 11W model gives 45 micromol/m^2/s and 13W modles gives 55 micromol/m^2/s at 12" distance. So if you measure the fc/lux at 12", you can calculate your own conversion factor.

Thank you for the info, Terry. Maybe I can use less light, too.

[Ray]

I don't how how reliable those numbers are, Naoki. They came from the manufacturer, are are the same lamp. How they can be tested at both 11- & 13 watts is beyond me.

[samfish]

I was also curious How, and Why, the would measure at 11 Watts and 13 Watts, since the lamp is used with standard AC Power and does not have a way to vary the intensity...

---------- Post added at 11:23 AM ---------- Previous post was at 11:19 AM ----------

Naoki,
If you have one of Ray's lamps, and a PAR Meter-- to measure PPFD and foot-candle, that would be great!!!

Thanks!
-sam

[samfish]

I measured Ray's 13W LED Lamp at a distance of 12", with my Luxmeter.

I measured 370 foot-candles, or 3900 Lux

Using the White LED Conversion Factor of 0.15 umol/m^2/sec per foot-candle, this gives 55.5 umol/m^2/sec

Which matches the data from Ray that ray has for the lamp, exactly!!!

So, I think using this at 12" will work fine for low-light, and I will use this as a baseline for my higher light plants, targeting up to 150umol/m^2/s for higher light plants!


Thanks very much for the info and help!
-sam

[naoki]

Sounds good, Sam. But you might need to adjust the distance as you go. Optimal level of light can be influenced by other environmental factors; temp, humidity, watering frequency etc as you probably have guessed.

Here is my measurement, which is somewhat different (room temperature 64F, the LED has been warmed up).

12" 38.5 micromol/m^2/s, 273 foot-candles
6" 140 micromol/m^2/s, 961 foot-candles

Actual energy consumption: 10.4W
Power factor: (PF) 0.99
Disatance measured from the LED surface.

The fc measurement is somewhat different between Sam's and mine, but it could be caused by several factors. (1) variation during the manufacturing process. It is possible that the factory has increased the quality control, and they are getting higher efficiency LEDs. (2) temperature influences the output a little bit. (3) It could be differences in the fc meter. Most of the cheap lux/fc meters we use don't have accurate response curve. The ideal response is like this (the black curve; from Wikipedia luminosity function):

(4) this is unlikely because the output decay of LED isn't so steep when they are designed well, but mine haven't been running at least 1 year.

But, the conversion factor is around 0.144 micromol/m^2/s per 1 foot candle with Ray's LED.

PPFD measured with Li-Cor LI-190 sensor + LI-185
fc measured with Dr.Meter LX-1330B

[terryros]

I just measured one of the ALT PAR 38 bulbs, 30 watts, from Orchids Limited in isolation from any other light. I used my Apogee PAR meter, which we know modestly underestimates the farther red part of the spectrum.

At 12 inches under the bulb I get about 70 micromoles/m2/sec and this diminishes to about 50 as you move about 8-10 inches out from the center point.

At the 9 inches or so that the tops of my Cattleyas are under these lights, in isolation you get about 130-140 micromoles/m2/sec. In the overlap zone between two lights you got somewhat higher readings.

On Slippertalk a few months ago I posted a picture of a three bloom Paph Maudiae 'Bankhaus' which had grown and bloomed under never more than 50 micromoles/m2/sec. I have three different plants of a tetraploid Phrag Don Wimber blooming under 80 micromoles/m2/sec at the top of the leaf zone, and I have a Cattleya Heathii (walkeriana x loddigessii) and a Vanda/Neostylis Lou Sneary just opening under 125-150 micromoles/m2/sec. I think all of these light levels would seem a little low for these plants, but with these bulbs they grow and bloom well.

I know their efficiency isn't at the top of the range and they aren't cheap, but the lenses are great and focus the light just to the growing area without wasting it in other directions and the heat dissipation design is supposedly first class. I can have buds within two inches of the bulbs and there is no ill effect. You can hardly feel any heat with your hand at this distance below the bulbs.


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[samfish]

Naoki and Terry,
Thanks for the measurements and data!!!

From this, I am moving my ALT PAR38 30-watt alot closer to my plants... Orchidweb says 3-4 feet for Medium-High, but obviously the true distance is quite a bit closer!!!

And, I will place Ray's lamps ~12 inches away from my low-light plants...

I will see how my plants respond, and adjust accordingly!!!