Help on led growlights

[DKkenn]

Hi,
Last november i bought 4 90cm full spektrum led lights.
They are single row leds at 15w pr light

I have put them about 10cm opart but would like some help on how close to the plants they need to be.

I did a umol measurement in different heights from the lights.

10cm: 120-260umol
20cm: 115-210
30cm: 90-160

I have attached a pic of the setup.

What height from the plants would you guys recommend the lights to be?

Thanks!

 

[CarlG]

Well, can you change the height? If so, then start with them as far as your setup will allow, and then move them closer until the plants look "bleached".

BTW, if you like math:
A point source of light follows the inverse square law: intensity = 1/distance^2.
However, using a linear array of lights, you have to account for each led in the array being a point source, so you need to solve the definite integral of that law, which is, for an infinitely long array, intensity = 1/distance. If you have multiple arrays, then you get into the second integral, which winds up being intensity = 1/ln(distance) [think I got that right, been a while since I did any calculus].

BTW, I know most of you don't care, but I'm annoying that way

 

[Ray]

Carl, the trouble is that each LED is a “patch” of many “points” if emission AND there is a linear array. It has been a zillion years since I did any calculus too, so I just won’t.

DK, as you have a PPFD meter, I think it’s better to just shoot for these, generally accepted levels for 12 hr/day exposure:

• Low-Light (Mottled-Leaf Paphs, Jewel Orchids, Phals)
  40–80 umol/m2/s
• Moderate-Light (Onc, Phrags, Epis, Dends etc)
  80–150 umol/m2/s
• High-Light (Cattleya)
  150–350 umol/m2/s
• Very High-Light (Vandas)
  350–600 umol/m2/s

 

[orchidlife]

Looks like the only plant you will have an issue with is the flowering phal? I grow under lights and have what appears to be much more light.
I havent measured accept with a phone app, I just pay attention to leafs.

 

[orchidlife]

Looks like the only plant you will have an issue with is the flowering phal? I grow under lights and have what appears to be much more light.
I havent measured accept with a phone app, I just pay attention to leafs.

On the top and bottom shelves the lights are pretty close (approx 6-8") but they are small plants in 2 or 3" pots

 

[DKkenn]

Well, can you change the height? If so, then start with them as far as your setup will allow, and then move them closer until the plants look "bleached".

BTW, if you like math:
A point source of light follows the inverse square law: intensity = 1/distance^2.
However, using a linear array of lights, you have to account for each led in the array being a point source, so you need to solve the definite integral of that law, which is, for an infinitely long array, intensity = 1/distance. If you have multiple arrays, then you get into the second integral, which winds up being intensity = 1/ln(distance) [think I got that right, been a while since I did any calculus].

BTW, I know most of you don't care, but I'm annoying that way

Thanks. Though I am not sure I understand what you are trying to say with the math thing..

Carl, the trouble is that each LED is a “patch” of many “points” if emission AND there is a linear array. It has been a zillion years since I did any calculus too, so I just won’t.

DK, as you have a PPFD meter, I think it’s better to just shoot for these, generally accepted levels for 12 hr/day exposure:

• Low-Light (Mottled-Leaf Paphs, Jewel Orchids, Phals)
  40–80 umol/m2/s
• Moderate-Light (Onc, Phrags, Epis, Dends etc)
  80–150 umol/m2/s
• High-Light (Cattleya)
  150–350 umol/m2/s
• Very High-Light (Vandas)
  350–600 umol/m2/s

Thanks. I think I will go with this. I will try and raise it a bit.

Looks like the only plant you will have an issue with is the flowering phal? I grow under lights and have what appears to be much more light.
I havent measured accept with a phone app, I just pay attention to leafs.

How many light you have pr shelf and how many watts are they? And yes, the flowers can't be under the lights..

 

[orchidlife]

Thanks. Though I am not sure I understand what you are trying to say with the math thing..


Thanks. I think I will go with this. I will try and raise it a bit.


How many light you have pr shelf and how many watts are they? And yes, the flowers can't be under the lights..

2 lights per shelf
36" and each one is 15watt

 

[southernbelle]

Looks like the only plant you will have an issue with is the flowering phal? I grow under lights and have what appears to be much more light.
I havent measured accept with a phone app, I just pay attention to leafs.

Correction: If you measure, be aware that it takes a light meter (F/C, LUX) or PAR meter (umols/s) specifically able to measure full spectrum if your lights are. When I was measuring with a PAR meter that was not specifically full spectrum 400-700, it measured about 20% off (low).

 

[southernbelle]

Thanks. Though I am not sure I understand what you are trying to say with the math thing..


Thanks. I think I will go with this. I will try and raise it a bit.


How many light you have pr shelf and how many watts are they? And yes, the flowers can't be under the lights..

Why can’t the flowers be under the lights? My lights are high intensity, so I can have the correct PAR at the top of canopy, and still have plenty of headroom for flowers. It all depends on the intensity of the lights and how much headroom they allow above canopy.

 

[Ray]

If you measure, be aware that it takes a light meter (F/C, LUX) or PAR meter (umols/s) specifically able to measure LEDs’. When I was measuring with a PAR meter that was not specifically for LEDs it measured about 20% off. If I remember correctly, it measured low.

A PAR meter is supposed to read the sum of the photon flux for all wavelengths between 400 & 700 nm - no matter what the source. If you were getting incorrect readings, I'd guess it had to do with the quality or calibration of the sensor, not the light source.

Ordinary light meters tend to capture the most photons in the vicinity of green.

 

[southernbelle]

A PAR meter is supposed to read the sum of the photon flux for all wavelengths between 400 & 700 nm - no matter what the source. If you were getting incorrect readings, I'd guess it had to do with the quality or calibration of the sensor, not the light source.

Ordinary light meters tend to capture the most photons in the vicinity of green.

Ray, I certainly can’t explain it, but Terry and I had the same PAR meter, the Apogee Quantum 100x and we have different brands of LEDs. But both of us experienced the same thing until we upgraded to the higher level meter that is full spectrum. Even the specs on the website say the 100x is not full spectrum. It measured 20-25% low.

 

[Ray]

I think we're in agreement.

True PAR is that rectangular dotted volume. Neither of the sensor response curves incorporate that full volume, but do add some photons outside of it. The black curve captures less than the gold one. If the lamps put out a lot of red and blue, the "black" curve just wasn't seeing it.

It's just a matter of investing in a better sensor, not one "designed for LEDs". The black sensor would have read low in sunlight, too.