Lighting an orchid closet - fluorescent or LED? Otherwise?

[DavidCampen]

You can use most any light meter for comparing the intensity of light sources. It doesn't have to be some so called "quantum par" light meter. I only say "most any" because the first one that I bought was absolute junk but the second inexpensive, Chinese made, meter that I bought is decent.

13 watts input is rather puny. For a first approximation you can say that an LED light is about equivalent to a T8 fluorescent. So, to match 70 watts input to T8s you need 70 watts input to LEDs.

As a supplemental light in my greenhouse I use an LED light bar that I built that uses 16 X 10-watt input LEDs. I use it for supplemental light in a 2X4 ft area.

Edit:
One additional point, foot candles (fc) or lux are much better for comparing light sources for plant growth than lumens.

[naoki]

Originally Posted by DavidCampen

You can use most any light meter for comparing the intensity of light sources. It doesn't have to be some so called "quantum par" light meter. I only say "most any" because the first one that I bought was absolute junk but the second inexpensive, Chinese made, meter that I bought is decent.

13 watts input is rather puny. For a first approximation you can say that an LED light is about equivalent to a T8 fluorescent. So, to match 70 watts input to T8s you need 70 watts input to LEDs.

Hi David, I'm not quite sure if I follow your logic. For measuring the intensity, you could use footcandle/lux, and you are right that these light meters are cheap. But we are talking about how effective the particular aritifical light is for photosynthesis, right? Would you use 550nm LEDs with 2000fc instead of 400nm LEDs with 1000fc to grow orchids? So radiant yield of sun light is around 43%, cool-white florescent light is 22-27%, and incadescent light is 6-7% (http://www.aos.org/Default.aspx?id=230). So comparing the intentisity isn't enough, is it? Maybe you are saying that the emission spectra of all LEDs are similar to each other? My understanding is that the emission spectra of LED and florescent lights have narrow peaks and ragged shapes. Also they have been tweaking LED to get better spectra. So it seems PAR is a relevant quantity than lux or fc. Am I missing something?

I think one person in a frog forum mentioned that Jungle Dawn LEDs are well tweaked, so he could flower Cattleya with them.

With regard to W equivalency between T8 and LED, here is some PAR measured by planted aquarium people (Lighting an Aquarium with PAR instead of Watts

An affordable decent LED light,
Finnex Ray II 24" DD (20W):
PAR = 87 micromols / m^2 / sec. @ 12"
PAR/W = 4.35

HomeDepot Diamond Plate shoplight (T8, 6500K, 32W x 2):
PAR = 118 micromols / m^2 / sec. @ 12"
PAR/W = 3.6875

So 100W of T8 is similar to 85W of LED. But there are lots of differences in PAR/W, especially for LEDs (and the quality of reflectors for T8).

[DavidCampen]

What I said is that PAR is the same as lux or footcandles, you only need to multiply by a constant of proportionality to convert from one to another.

So 100W of T8 is similar to 85W of LED. But there are lots of differences in PAR/W, especially for LEDs (and the quality of reflectors for T8).

Yes, exactly as I said, to a first approximation, 1 watt of fluorescent is equivalent to 1 watt of LED.

[Magnus A]

As PAR is the light intensity measured between 400 and 700 nm it is usually the same as measure the lumen with an ordinary light meter for ARTIFICIAL light.

There are very little light from a light source (for growing) below 400nm. For wavelength over 700 nm (near IR) contain very little energy and therefore contribute very little to the measurement. This mean that an ordinary light meter reading in lumen give a pretty good value also in PAR.

[naoki]

David and Magnus, you are right. I have thought that PAR doesn't include the green lights in the measurement, but the definition of PAR includes it. So PAR isn't as useful as I thought (especially for LED with sharp peaks). What I was talking about is more related to Photosynthetically Usable Radiation (PUR), but this isn't easy to measure. 550nm (green) light is useless for photosynthesis, because it gets mostly reflected by leaves. Well, I could use my Li-Cor to measure photosynthetic rates under different light source, but I guess I should leave orchids as a hobby.

[Magnus A]

Originally Posted by DavidCampen

Yes, exactly as I said, to a first approximation, 1 watt of fluorescent is equivalent to 1 watt of LED.

This statement is not correct as the stated effect in watt a lamp has is measured on the electrical side. How much electricity is needed to drive the lamp in a proper way. The light output is then defined by the luminous efficacy (lumen / Watt) of the particular lamp technique.

It is important to differentiate the energy in (Watt) from luminous power out (lumen) when talking illumination.

The luminous efficacy for different light sources differ quite alot and 1 Watt LED does not give the same luminous power as 1 Watt LED!

[Ray]

Originally Posted by fishmommy

The thing I have been reading about LEDs that is interesting is you need to supply some stressor like a heat source and fan for robust plant growth.
I have seen sites that recommend against pure LED setups and instead recommend hybrid setups so that some heat is generated by the traditional lights.

It's so hard to tell on most of these plant lighting sites if the advice they are giving is really targeted at the needs of pot plants or is the advice more general. I hate that.

I don't think such "stressors" are necessary. Rob (L'il Frog)has been growing under red/blue panels with great success (do some searching here to find his posts).

I am fascinated by the Jungle Dawn lights, as they are white, not colored, so when used in the living environment, look a lot better.

I bought this one to keep an African violet alive that my wife put in a dark bathroom.

[DavidCampen]

Originally Posted by Magnus A

This statement is not correct as the stated effect in watt a lamp has is measured on the electrical side. How much electricity is needed to drive the lamp in a proper way. The light output is then defined by the luminous efficacy (lumen / Watt) of the particular lamp technique.

I am not saying anything different. The current state of fluorescent lamp technology versus LED technology is that they have about the same efficacy in converting input power into photons.

It is important to differentiate the energy in (Watt) from luminous power out (lumen) when talking illumination.

Yes, thank you for clarifying this, often things are so obvious to me that I neglect to give the detailed explanations that are needed for others to understand.

The luminous efficacy for different light sources differ quite alot and 1 Watt LED does not give the same luminous power as 1 Watt LED!

Again, the current state of fluorescent and LED technology is that they are about equivalent. I am hoping to see improvements in the efficacy of LEDs that would make them significantly more efficacious than fluorescents but that has not yet happened.

[Magnus A]

Originally Posted by DavidCampen

Again, the current state of fluorescent and LED technology is that they are about equivalent. I am hoping to see improvements in the efficacy of LEDs that would make them significantly more efficacious than fluorescents but that has not yet happened.

I am now testing a LED panel with white light that gives 110 lm/W. As T5 fluorescent with good spectra give about 75-80 lm/W (OSRAM DULUX® L LUMILUX®) the difference is significant.

LED technology moves FAST!

[DavidCampen]

Originally Posted by Magnus A

I am now testing a LED panel with white light that gives 110 lm/W. As T5 fluorescent with good spectra give about 75-80 lm/W (OSRAM DULUX® L LUMILUX®) the difference is significant.

LED technology moves FAST!

We are talking about lights for plant growth not human vision. Lumens is a fairly useless metric for evaluating lights for plant growth. The lumen metric is strongly weighted to human vision. You could have an LED emitting 200 lumens per watt of 555 nm light and it would be less efficacious for plant growth than an LED giving 20 lumen per watt at 660 nm.