Brightness with LED Lights - Orchid Board

samfish · #1 10-04-2015, 07:28 PM

I recently moved, and am starting to grow indoors with LED lights (I used to grow mostly outdoors)

I am trying to figure out how much light my plants are getting, and how far away to put the LED Lights

The readings with a photometer are way off, and are much lower than what I would expect outdoors...

Is there a way to tell how much light (or equivalent foot-candelas) plants are getting, when growing indoors with LED lights?

estación seca · #2 10-04-2015, 07:49 PM

You need to contact the manufacturer to get data for your particular lights. There are so many different LEDs manufactured, and so many different kinds, it is not possible to generalize.

naoki · #3 10-05-2015, 02:58 AM

I'm guessing that you are using R+B type LEDs since you mentioned that the reading of the light meter is off. Since different models have different mixture of colors, lux/fc meters have limited usefulness. If you really want to know how much plant relevant light they are getting, you can use Quantum PAR meters. But the cheap models cost about $200. "Light measurement" of the following post has some relevant links:
LED related links

kwubb · #4 10-11-2015, 03:03 PM

You can't measure LED lights with a meter. Mine are natural white and can't be measured. I use 3 methods. Place a finger or hand between you and the plant. I don't remeber all the details but a nice crisp shadow a certain distance away is a lot of light and so forth. Watch your growth. Short and stubby is too much light long and leggy too little. My favorite is utilizing a plant calleded Cryptanthus, a Bromelioideae. I had a mother plant that was variegated green and white. I placed the babies at various positions around my lights. When it receives lots of light the white turns a vibrant pink. Less light produces duller shades until it remains white. Stumbled on this by accident but it works great and doesn't take days. Now if I can just find some more Cryptanthus.

Ray · #5 10-13-2015, 09:48 AM

Why can't you measure LED output with a light meter?

kwubb · #6 10-13-2015, 02:40 PM

I'm not sure Ray. I was asking the people at the orchid greenhouse I use why I was getting weird readings with my digital meter. He told me I couldn't get readings on my lights with a digital meter. If he explained further I have forgotten. Therefor I assumed it was true on all LED lights, but you know what they say about assuming.

Ps: on another note I'm interested in trying your probiotics and sent off an email to your site a couple days ago. When you have a spare moment (what are those) I'd love to communicate with you about the questions I sent. Although I may have figured it out and may just go ahead and order soon. Sorry this may not be the appropriate place for this note.

terryros · #7 10-14-2015, 10:47 PM

As Naoki noted above, you can measure light levels with LEDs using a PAR meter. The measurement is micromoles/meter squared/second, which is how many photons in the photsynthetically active range that are hitting an area. While most of the meters aren't perfect (mine has a little fall in sensitivity at one end of the spectrum) these are much more accurate than standard lux/footcandle meters.

The remaining problem is that we don't have enough information yet about the minimum/maximum "photon flux" per day that any particular orchid genera needs to grow and bloom optimally.

I have been using LEDs for over 4 years and measuring light with a PAR meter for over a year and my early results suggest that the photon flux needed for at least some genera is less than what we thought from green house/natural light conditions. I have some hints, supported by one study in nature that I found, that the focusing lens of the LEDs might affect some of this. A light source that is very vertically focused may be seen as more intense by some leaves than the same photon flux coming from the diffuse light of natural light. More work needs to be done,

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kwubb · #8 10-15-2015, 08:53 AM

terryros thank you for this information. Can I ask what kind of LED lights you use, wattage etc. in light of the fact that many of us have digital meters at the best, and with your experience with LEDs, are you able to offer suggestions to the initial guestion regarding distance placement of these lights from the plant. I mostly just watch the plants but that can be a long process. I have some that are as far away from the lights as I can get them and I think they are still receiving too much light. I'm going to try a piece of shade cloth over one light and see if this helps. I do hope further work is in progress and that soon someone(s) are able to shine a little light on this subject.

samfish · #9 11-06-2015, 06:52 PM

So, is there any way to use a LUX Meter, and use some conversion factor to determine the "equivalent intensity" of an LED Light?

Basically, I am trying to figure out how far to place an LED Light, for:
Phalaenopsis (1200-1500 ft-candles)
Cattleya (3000 ft-candles)

Are there any rough guidelines or ways to figure this out?

terryros · #10 11-06-2015, 07:57 PM

Naoki has some rough math to get a conversion from footcandles/lux to micromoles/m2/sec photon flux density, but getting a specific PAR meter that measures photon flux density in the most photosynthetically active range is better. The PAR meters that are affordable aren't perfect, but they are far superior to a standard FC/LUX meter.

You can't give a blanket distance of an LED from the plants because it depends completely on the specific light and whether the light is focused downward or not.

With a 40 degree dispersion lens on an MR16 bulb delivering about 650 lumens at 7 watts, I can have the bulbs about 24 inches away and get around 50 micromoles/m2/sec in the leaf zone which has been surprisingly good at growing and blooming Phals and Paphs. I use 60 degree dispersion bulbs delivering 1050 lumens at 15 watts at a height of about 14 inches and get 100-150 micromoles in the leaf zone and this is growing and blooming Cattleyas and Neofinetias. Finally, I have four 100 degree dispersion lights delivering about 2400 lumens at 30 watts and I have these at about 9 inches above the leaf zone for tall Cattleyas. But, I can vary the heights of plants under any of the lights to achieve the illumination I want, so I have Miltoniopsis farther away from the 100 degree bulbs at about 100 micromoles/m2/sec and Phrags a little closer to the 40 degree bulbs to get about 80 micromoles/m2/sec.

All of my lights are from ALT. They are not cheap, but I am paying for the lensing and the superior heat dispersion. I am trying to illuminate areas that are about 20-24 inch wide so have the lights as track lighting over about four feet lengths. I don't have the skill or passion to build the LEDs myself!

I think the micromoles/m2/sec measurements for orchids that have come to us from greenhouse/outdoor conditions may not quite apply to LED lights focused downward on plants. In my conditions, 50 micromoles/m2/sec is fine for lower light plants, 80-100 for medium, and by 150 micromoles/m2/sec high light plants are growing and blooming. All achievable by LEDs.

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