how tall for a 400w ?

I was just wondering if anyone knows or has a link to an explanation of how much penetration you get from a 400w MH / HPS.

Hi SHame... Ifyou are using ONE 4 watt bulb you can grow 9 plants and flower than at 6-12 nodes and get the same harvest as if you waited until they had 24 nodes....

If the canopy is tight penetration will only be 1-4 inches.... If you are growing a single plant under a 400 watt bulb you may be able to let the plant get 20-24 inches tall... after that, the penetration to the lower branches is pathetic and does not produce any significant buds....

And the plant will become unruly and start to lean... etc..

iloveyou

So if I am trying to do 6 plants for instance , under that 400w light I should prob start flowering them at about a foot tall ? And I have to train them or something to get the light past the canopy? Or am I growing just for tops?

shamegame said:

I was just wondering if anyone knows or has a link to an explanation of how much penetration you get from a 400w MH / HPS.

Click to expand...

It depends on how far away from the plant canopy it's used at.

HID lights (HPS and MH) and all single point light sources (except the sun) are all restricted in terms of their luminous flux by the 'light intensity = Output divided by distance squared'' rule.

So for a 400w HPS outputting something like 50,000 lumens at 1 foot distance, at 2 feet distance it will output 50,000 lumens divided by distance (2 foot, squared, so 2 x 2) = 50,000/2x2=12,500 lumens at 2 feet distance. At 3 foot it's the same so, 50,000/3x3= 5,555 lumens at 3 foot distance.

So that gives you an idea of how to calculate the light penetration of a 400w HPS.

Here dude, this chart may help ya.
Peace

Gr8 chart, VM. Thanks for the info.

Yeah right on with the chart man- exactly what I Needed.

Cheers.