Lighting question I've exhausted all options trying to answer.

Many professional grows seem to keep their lights much higher than 24"-36" from the canopy. I've exhausted all resources and can not answer why this is common. Is the not a huge decrease of PAR output after 36"?

-GreenCountryGrower

DE-HPS is mounted higher for a coverage area of 6x6 due to high light and heat output. Admittedly it is not the most efficient lighting method but it seems to be the most popular setup since high intensity LEDs can only cover up to 4x4 with lower mounting distance and are 2-3 times more expensive. LECs are another option but are only rated for 3x3 areas which means purchasing 4x more fixtures that are around the same price as DE-HPS fixtures. There are some commercial facilities who have been willing to invest in the newer lighting technologies to save electricity but most seem to be happy with the proven DE-HPS method. A good analogy is that expensive electric vehicles are not very popular compared to cheaper vehicles with the time-tested internal combustion engine.

They stick multiple lights up high so they get an overlaping pattern. Light in the area of overlap is more intense

Thank you both, I figured that they were getting a larger spread being further away, I just wasn't sure the lights would still be efficient. You would need 1000w to efficiently cover a 6x6 area wouldn't you?
I use a 630w DECMH for a 4x4 area. I have wondered if I could get away with raising the lights and trying a 6x6 with it.

GreenCountryGro said:

Thank you both, I figured that they were getting a larger spread being further away, I just wasn't sure the lights would still be efficient. You would need 1000w to efficiently cover a 6x6 area wouldn't you?
I use a 630w DECMH for a 4x4 area. I have wondered if I could get away with raising the lights and trying a 6x6 with it.

Click to expand...

More often than not, folks will use 2 x 600W in that area vice a single 1000 watter. IMHO when you start getting into this type of set up, one should be using a par meter, to determine the latter. That being said you will be generating twice as much heat. Perhaps twice as much is a figure of speech, you catch my drift. Everything is relevant.

I came across this useful formula (A*P= desired PPFD) the result divided by 1.4 = watts required). (I don't remember where I ran across it), where:

• A = area in square meters. (ft2/10.7639) = M2
• P = PPFD required (750)

In your situation... 6x6 = 36ft2 = 36/10.7639 = 3.3 M2

a 6x6 (3.3M2) x 750 = 2475 PPFD (desired)
2475 PPFD divided by 1.4 = 1767W required

a 5x5 (1.52 M2)= 814W required

Although only a delta of an extra square foot, the area has more than doubled

Your current set up (4x4)= 771W req'd.

Hope this helps

GreenCountryGro said:

Many professional grows seem to keep their lights much higher than 24"-36" from the canopy. I've exhausted all resources and can not answer why this is common. Is the not a huge decrease of PAR output after 36"?

-GreenCountryGrower

Click to expand...

If you take a class in Electro-magnetics, statics, one of the mathematical proofs you do involves a plane of light.

Basically, if you have an infinite plane of light, distance from the light source doesn't matter.

The large grows don't have an infinite plane, but the physics can be similar.