LEDs

[Dorsetman]

I;m hgere under false pretences - I am hardly a new grower after nearly 60 years !

But I am thinking of rejigging the lighting set-up I use for my cattleyas in particular. Going to LEDs for fairly obvious reasons .

I find that many units have a notional wattage, and then say they use much less. For example I am looking at Kinghbo 1000 watt units, said to use 200 watts . How can this be right ?

Any ideas, folks ?

[Palancar]

You are getting the equivalent light output of 1000 watts of light using leds with a power usage of 200 watts. Other factors that come into play is whether the diodes have lenses attached. This would determine the intensity and area of coverage of the light. Hope this helps.

[Tyrfing]

Possibly they try to compare the light output to traditional HID (that they claim their 200 W LED is equivalent to 1000 W HID)?
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[raybark]

It isn't right. A 200 watt lamp is a 200 watt lamp. Here in the US, pretty much all consumer light bulbs are labeled and sold under "equivalent" pretenses - equivalent to the light output of an incandescent bulb, as perceived by the human eye.

[Dorsetman]

The really important questions are two- how many lumensthe lamp produces, and how many dollars/pounds/euros, my electricity supplier wants at the end of the month.

But, am I even right here ? I have seen lumens output quoted for LEDs, but I have a feeling that this measure applies to white light , and falls down when the lighting unit has a mixture of red, green, and sometimes infra-red too , rather than all white LEDs. Anyone put me right ?

[Tyrfing]

Lumen is used for visible light.

One LED has quite a narrow wavelength. A LED lamp (with lots of LEDs) might also have a more narrow/specific wavelength range compared to other light sources.

I have noticed that some producers of LED lamps for growing prefer to specify the amount of light using PPF (photosynthetic photon flux, unit μmol/s) or PPFD (photosynthetic photon flux density, unit μmol/s•m²) in the PAR (photosynthetically active radiation) range (400–700 nm). I think this makes some sense, but it also makes it harder to compare to other light sources (or plant requirements which is often in the archaic foot-candles unit).

I tried to check a bit on LEDs a year ago when I bought some LED lights for my growing tank. I gave more or less up, and just bought something marked "Grow". Both my plants and I have been happy ever since.

[Dorsetman]

I tried to check a bit on LEDs a year ago when I bought some LED lights for my growing tank. I gave more or less up, and just bought something marked "Grow". Both my plants and I have been happy ever since.

I like this. It willbe my philosophy -fingers crossed...

[raybark]

To be more specific...

Lumen is used for visible light.

...the PAR region of the spectrum is visible light, as well. The difference is that PAR is dealing with everything in the 400-700 nm range of wavelengths, while a lumen is an evaluative measure because it is how bright the light source appears to the human eye, which is more sensitive to green.

One LED has quite a narrow wavelength. A LED lamp (with lots of LEDs) might also have a more narrow/specific wavelength range compared to other light sources.

You're forgetting white LEDs, which mimic a fluorescent lamp's functional model - a blue or UV LED excites a phosphor, which responds by emitting a number of different wavelengths that combine to be "white". I use quotes because, just like fluorescents, that can be adjusted for whatever purpose the lamp is intended. A "home lighting" "White" LED will have a range of peaks, but will predominately green, again because it will look brighter to the human eye. By varying the wavelength ratios, we come up with the various correlated color temperatures or "Grow Lights".

I have noticed that some producers of LED lamps for growing prefer to specify the amount of light using PPF (photosynthetic photon flux, unit μmol/s) or PPFD (photosynthetic photon flux density, unit μmol/s•m²) in the PAR (photosynthetically active radiation) range (400–700 nm). I think this makes some sense, but it also makes it harder to compare to other light sources (or plant requirements which is often in the archaic foot-candles unit).

Actually, it makes a lot more sense because it tells you how much energy is being provided to the plant. A red and blue LED lamp and a white lamp of ANY source, if they have the same PPF, will have a similar benefit to plants, even thought the foot-candles, lux or lumens from them will be totally different. Again, FC, Lux, and lumens are all based upon human eye perception; PPF is plant-centric, making it of a lot more utility.

Apogee Instruments lists some rough conversions, depending upon the type of light source.

---------- Post Merged at 06:14 PM ----------

I'll add that the conversion from old culture sheets isn't all THAT tough...

Full sunlight at noon at the equator is 10,000 foot-candles and 2000 µmol/m2/sec, so the conversion factor is simply 10000/2000=5. Since culture sheets tend to give maximum light intensity recommendations, in order to duplicate the same number of photons hitting the plant per unit time when used continuously, you simply divide those foot-candles by 2, making the "Culture Sheet" natural light FC recommendation, divided by 10, gives you the µmol/m2/sec your lights should provide.

[Tyrfing]

You're forgetting white LEDs, which mimic a fluorescent lamp's functional model - a blue or UV LED excites a phosphor, which responds by emitting a number of different wavelengths that combine to be "white". I use quotes because, just like fluorescents, that can be adjusted for whatever purpose the lamp is intended. A "home lighting" "White" LED will have a range of peaks, but will predominately green, again because it will look brighter to the human eye. By varying the wavelength ratios, we come up with the various correlated color temperatures or "Grow Lights".

True, the point that I was trying to make (and failed to make explicit) is that a high output narrow band LED lamp might have a low lumen rating.