Light intensity vs ppfd/DLI

[PeaceLove&Buds]

Using approximate numbers and ideal tent conditions for an example…lets say one plant is getting 800 ppfd and is 24” away from light at 60% power and one is getting 800 while 36” away at 100% power. Will they equally prosper or will the lack of higher intensity affect the finish?

 

[BII]

Plants receiving the same ppfd are essentially receiving the same amount of photosynthesis-relevant light.

The ppfd is a measurement of light intensity, the collective amount of photon-delivered energy relevant to photosynthesis. Much as 800 watts of electrical power (watts = volts x amps) is 800 watts whether the circuit is 80 volts at 10 amps or 400 volts at 2 amps, 800 ppfd is/equals 800 ppfd irrespective of the light distance and power.

 

[PeaceLove&Buds]

Plants receiving the same ppfd are essentially receiving the same amount of photosynthesis-relevant light.

The ppfd is a measurement of light intensity, the collective amount of photon-delivered energy relevant to photosynthesis. Much as 800 watts of electrical power (watts = volts x amps) is 800 watts whether the circuit is 80 volts at 10 amps or 400 volts at 2 amps, 800 ppfd is/equals 800 ppfd irrespective of the light distance and power.

Thank you very much!

 

[BII]

But upon thinking, there could be some differences in plant growth at different heights, such as different levels of penetration and reaching lower shaded leaves with a light putting out the same ppfd being closer vs. more distant from the plant. When closer there is more light penetration to lower levels (with non-point sources, such as a quantum board vs. AutoCOB), due to more light coming from different angles.

Presuming you can adjust light power/intensity, I favor lowering the lights and as needed backing off on intensity settings, particularly during bloom. I'd want the better penetration and also use less electricity.

 

[PeaceLove&Buds]

But upon thinking, there could be some differences in plant growth at different heights, such as different levels of penetration and reaching lower shaded leaves with a light putting out the same ppfd being closer vs. more distant from the plant. When closer there is more light penetration to lower levels (with non-point sources, such as a quantum board vs. AutoCOB), due to more light coming from different angles.

Presuming you can adjust light power/intensity, I favor lowering the lights and as needed backing off on intensity settings, particularly during bloom. I'd want the better penetration.

I agree and this is the angle I hoped would be an advantage. I had two tents with 4x4 630watt leds and they’ve proven costly when running at /near full power together. I’m hoping that being in a 4x8 now I could run each at 60% max.

 

[BII]

I agree and this is the angle I hoped would be an advantage. I had two tents with 4x4 630watt leds and they’ve proven costly when running at /near full power together. I’m hoping that being in a 4x8 now I could run each at 60% max.

We agree, but before deciding a course of action, get some confirmation. [Can anyone besides me comment?]

 

[PeaceLove&Buds]

We agree, but before deciding a course of action, get some confirmation. [Can anyone besides me comment?]

Hahaha don’t worry because I’m a very ”hands on gotta see it for myself” kinda guy and would be trying this anyways, just curious of anyone’s experience. I look to the plants to tell me what they need and they’ll let me know if they’re happy or not. There’s some aspects of growing that I’d rather fail at and see how/why/when for myself than relying on the science, but I’m always eager to learn other growers experiences. My power bill comes every two months and I’m trying to dial in my minimum expenditure before the hot months come and the house AC is running a lot. Pretty sure I’ve been running this big light unnecessarily high. I really appreciate the conversation B.

 

[Mañ'O'Green]

@PeaceLove&Buds I bought 2 ChilLeds 500w Growcraft lights for a 4x6 space with the idea that I could run them at 50% or less and get the same DLI as running one at full power. The lights are so much more efficient at the lower power that it has worked very well for me and the heat in the tent is lower also. So yes what you are thinking is most likely correct with your lights as well.

I live in the San Joaquin Valley of California and hot is an understatement. I use a swamp cooler most of the summer which helps the low RH also.

I use the Photone app calibrated for my lights and it lets me know how the lights are producing in the different parts of the space.

 

[PeaceLove&Buds]

@PeaceLove&Buds I bought 2 ChilLeds 500w Growcraft lights for a 4x6 space with the idea that I could run them at 50% or less and get the same DLI as running one at full power. The lights are so much more efficient at the lower power that it has worked very well for me and the heat in the tent is lower also. So yes what you are thinking is most likely correct with your lights as well.

I live in the San Joaquin Valley of California and hot is an understatement. I use a swamp cooler most of the summer which helps the low RH also.

I use the Photone app calibrated for my lights and it lets me know how the lights are producing in the different parts of the space.

Thank you @Mañ'O'Green thats great to hear. I’ve been in your neighborhood and can empathize with the heat. I’m somewhat your neighbor down in LA county South Bay but less than a mile from the beach. Luckier with the heat but the humidity jumps from 25% to 82% like every 12 hours so that’s my biggest pain and I’ve usually got the room humidifier or de-humidifier running in the shed. A big advantage to running both lights is not only for my granddaughters veggies, but for my ability to sprinkle some 1gal freebie pots around the tent. One thing we do share is California’s ridiculous electricity costs. Cheers

 

[PeaceLove&Buds]

Ok the experiment is on. Plants are about 18-20” away at 60” power getting 750-825 ppfd. I‘ll have a close eye on them looking for complaints. Hopefully trying this at 60+ days old doesn’t mess with their minds too much but I guess that’s what the cured bud in the cooler is for!