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  #31  
Old 11-27-2018, 06:13 PM
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Color temperature in degrees Kelvin measures the appearance of light color to the human eye. Color temperature was never intended to measure utility for growing plants. With LED lights color temperature provides no information on whether the light is good for growing plants. You need to look at other measurements.

On a practical note, any fixture designed for growing plants should provide a spectrum useful for orchids. Intensity of light emitted, measured in foot candles, lux, lumens or moles of photons per square meter, is very important. Most people figure it out by buying a fixture, putting the plant under it, and watching what happens. With plenty of light, orchids begin turning purplish. Dollythehun mentioned this above.
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  #32  
Old 11-27-2018, 08:13 PM
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Understood, but spectrum analysis also seems central to any serious conversation about plant growth. Grow light vendors are not necessarily trustworthy regarding spectrum analysis. And many experienced orchid growers are receiving good results from household LED bulbs. I am coming to understand intensity measurements for LEDs in a practical sense, which has been comforting. But not making any real progress for detecting the actual spectrum of a LED bulb for practical purposes. I've seen videos of people waving a handheld instrument under a grow light fixture and apparently capturing a picture of the spectrum. What are those things??
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  #33  
Old 12-08-2018, 03:43 PM
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I believe the instrument you are referring to is a par meter and the price of those instruments are expensive for the professional ones.
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  #34  
Old 12-08-2018, 04:08 PM
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Quote:
Originally Posted by stompy View Post
I think the spectra depends on the LED type that's used. So you can have 2 LEDs that arecolor balanced to 3.5K but puts out very little blue vs the other puting out more blue. Check the spectra of the LED's. I made sure to check the timber ones before I bought
As has been stated, the color temperature of a fluorescent or LED lamp is how it LOOKS to the human eye, and not what the true spectrum is. All white LEDs are UV or blue diodes that have a phosphor that absorbs those wavelengths and emits wavelengths that combine to appear white. All such LEDs have plenty of blue, but little red.

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I believe the instrument you are referring to is a par meter and the price of those instruments are expensive for the professional ones.
Actually, a PAR meter tells you the volume and rate at which the lamp emits photons between 400 & 700 nm, but no information about the spectrum. It can be all red, all blue, white, or any combination in between, and the reading from a PAR meter can be the same.

Ideally, a PAR meter in conjunction with a spectrophotometer would tell us everything we need. I doubt any of us can afford that.
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Old 12-08-2018, 07:45 PM
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The manufacturer may have spectrum information available that is not on the retailer's Web site.

---------- Post added at 04:45 PM ---------- Previous post was at 04:44 PM ----------

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...Ideally, a PAR meter in conjunction with a spectrophotometer would tell us everything we need. I doubt any of us can afford that.
An uncle sold GE commercial spectrophotometers in the 1960s-1970s. He did well.
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  #36  
Old 12-08-2018, 09:34 PM
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As has been stated, the color temperature of a fluorescent or LED lamp is how it LOOKS to the human eye, and not what the true spectrum is. All white LEDs are UV or blue dioxides that have a phosphor that absorbs those wavelengths and emits wavelengths that combine to appear white. All such LEDs have plenty of blue, but little red.
Fascinating statement, Ray. Just to be clear, are you saying that even though this phosphor you mentioned masks blue wavelengths for appearance sake, that these wavelengths are nonetheless being emitted? This shows me up embarrassingly in what I don't know about light!
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  #37  
Old 12-09-2018, 09:10 AM
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Fascinating statement, Ray. Just to be clear, are you saying that even though this phosphor you mentioned masks blue wavelengths for appearance sake, that these wavelengths are nonetheless being emitted? This shows me up embarrassingly in what I don't know about light!
I'm sure those wavelengths are attenuated quite a bit, but some are still emitted.

This may seem a bit counterintuitive, but the "color" and brightness of white LEDs has quite a bit to do with how much green they emit, as that's where the human eye is most sensitive.
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  #38  
Old 12-09-2018, 01:15 PM
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Does an LED have a native color, by virtue of what it is?
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  #39  
Old 12-09-2018, 01:30 PM
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Does an LED have a native color, by virtue of what it is?
Yes. An individual Light Emitting Diode is a speck of one compound. When electricity is applied electrons orbiting the atoms in the LED are excited into a higher-level orbital. When they fall back into their normal orbital they emit a photon of light. The wavelength of light for any given compound will be the same each time this happens. An individual LED emits only one wavelength. Manufacturers combine LEDs emitting different wavelengths to make fixtures emitting white light.

In colored strings of LED lights each lamp generally emits only one wavelength of photos.
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Old 12-09-2018, 03:59 PM
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In colored strings of LED lights each lamp generally emits only one wavelength of photos.
Which is why a white LED is constructed similar to a fluorescent tube - the LED emits a wavelength that excites the phosphor painted over it, and that is what emits the visible light we see.

I don't know if there are any readily available chips yet that have a phosphor "tuned" for plants, but I sure wish there were.
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