Is this the correct formula to figure out Watts if I can't raise the height?

I have some ProGrow 680W lights with the controller box in my tent that is only 2m tall.

I obviously can't raise the lights anymore so adjusting the power is the next most useful tool. I just want to make sure this is the right formula

Manufacturer recommendation in late veg is 100% power at 115-130cm above canopy (avg 122.5cm)

The measured height above my canopy at the moment is 70cm

so...


70/122.5 = 0.57 (57%)

680x0.57 = 387.6

SO

I set my lights to 388W while they are 70cm above my vegging canopy.... does this sound about right?

I ordered an Apogee light meter so just wanna know if I can rely on this formula until that arrives

Just seems weird that at this stage I'm only using 776w of power on lights as opposed to 1800w when I was using HPS

"The intensity of the light to an observer from a source is inversely proportional to the square of the distance from the observer to the source. This shows that as the distance from a light source increases, the intensity of light is equal to a value multiplied by 1/d2. Thus closer a light source brighter it is. "(from Toppr).

-OR- get a cheap Lux meter for $25

Hugo Phurst said:

"The intensity of the light to an observer from a source is inversely proportional to the square of the distance from the observer to the source. This shows that as the distance from a light source increases, the intensity of light is equal to a value multiplied by 1/d2. Thus closer a light source brighter it is. "(from Toppr).

-OR- get a cheap Lux meter for $25

Click to expand...

I have a lux meter but from what im reading its not a great indicator of PPFD?. In any case, sticking it under my LEDs at the canopy at the above mentioned intensity (388w) gives me about 54k in the middle.

When i was running HPS i was shooting for 75k

Given that these lights have a high CRI rating, and most online guides seem to suggest a 400w sits about roughly the same height I now have them set at, I figured I'm probably somewhere on the right track..?

ketamine_disposal_unit said:

I have a lux meter but from what im reading its not a great indicator of PPFD?. In any case, sticking it under my LEDs at the canopy at the above mentioned intensity (388w) gives me about 54k in the middle.

When i was running HPS i was shooting for 75k

Given that these lights have a high CRI rating, and most online guides seem to suggest a 400w sits about roughly the same height I now have them set at, I figured I'm probably somewhere on the right track..?

Click to expand...

I suggest you let the plants decide the appropriate light intensity and numbers. If you're in a tent with about 7 foot ceiling you will have a very hard time making use of all that light if you don't supplement with CO2.

I would raise it to final height and let the plants grow in to it. Dimming it if you need to. Follow manufacturers guidelines and numbers will only give you problems. It's like thinking every single human being has dark skin and can take as much sun rays and radiation as a Caucasian. Humans have different race and somatypes while plants have different phenotypes and traits.

Wastei said:

I suggest you let the plants decide the appropriate light intensity and numbers. If you're in a tent with about 7 foot ceiling you will have a very hard time making use of all that light if you don't supplement with CO2.

I would raise it to final height and let the plants grow in to it. Dimming it if you need to. Follow manufacturers guidelines and numbers will only give you problems. It's like thinking every single human being has dark skin and can take as much sun rays and radiation as a Caucasian. Humans have different race and somatypes while plants have different phenotypes and traits.

Click to expand...

Ive always just left the lights at final height and done that but they grow weird. Mostly just really short and squat witb ridiculously tight nodal spacing. I think they're too powerful to be running at 100% at 70cm above canopy

The manufacturer guidelines only specify 100% power