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marijuana fueled

How far to hang my 400 Watt HPS light over my plant tops

Whats a good height to have a 400W HPS Light over my plant tops?

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18-24 inches mate but the closer the better , i find if i point an osc fan at the bulb i can get pretty close

put your hand above your plant top and hold it there for a minute , if its uncomfortable for you it will be for them :spliff:

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when correctly cooled : one foot

( one fan aimed at bulb . another aimed between canopy and bulb)

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when correctly cooled : one foot

( one fan aimed at bulb . another aimed between canopy and bulb)

i use 2 fans, 9in oscellating fan on the floor, 18in oscellating fan raised blowing over top of plants

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I can get my 600w (adjustawing reflector) about 14" away from my canopy (without any heat shield) it all depends on the enviroment as well as the reflector you are using. some disperse heat better, mine is an open ended one so with a fan pointing at it the heat from the bulb is taken straight away from the canopy.

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having your lamp closer isn't always better, the inverse square law everyone rants on about doesn't really apply to us, as our point source has a fuck off great reflector behind it, and therefore the light doesn't radiate off in all directions.

by following the "closer is better" train of thought, people often do worse because they have poor light spread.

when designing lighting schemes for building, you have an illuminance level that must be attained (for workshops you need 500lux at working level), when you buy a luminaire you get a light footprint that that luminaire produces, determined by the shape of the reflector and the intensity of the lamps, if you do some research you will find that the intensity of the footprint doesn't drop of due to distance as much as it is determined by the shape/quality of reflector (although it does eventually begin dropping off with distance, because it's hard to design a reflector that will get all the light point straight down perfectly)

because most reflectors we use are adjustable to some point, the way to get the best out of your lamp is to switch it on in your grow space and see where the footprint of the light falls, adjust this to cover the area of your plants while keeping a safe distance from your plants, there's no need to get your lamp right up close, because this way you have really high intensity directly underneath, but the only way you can have a higher intensity in directly underneath your lamp, is by losing intensity around the sides of your grow, as long as your shade is adjusted properly, you don't lose light by having the amp further away, it's just distributed more evenly (this only works up to a point, as even the best reflectors don't produce a perfect footprint, but within a couple of feet this is going to be minimal, and if your grow is wall to wall with plants this will be even less, because light is reflected from the walls)

basically it is just as important if not more to have a good even light spread, than having your lamp as close as it can be. 18" is more than adequate for a 400w and you can be sure the plants at the side of your grow are getting as much light as the plants in the middle

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9 inches seems about optimum for my 250s so I would say 12 inches sounds right for a 400.

I'm a great fan of getting the lamp deep into the canopy :-

post-14131-1209979036_thumb.jpg

Some people go the whole hog, ditch the reflector completely and grow the plants 360 degrees around a vertical lamp.

Edited by compostverte

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If you don't need to cover too far then get it close as possible. My 400s sit about 12 inch away (open ended reflectors) but even plants that come a little closer don't get burnt. There is a couple of fans blowing towards the lights as Cory-and-Trevor described.

Like Scraglor says though, don't forget about the poor beggars around the edge, you do lose quite some footprint as the light is lowered. :wink:

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Thanks for the help guys...I have it up pretty high right now because i read the higher the better.And I found it helped me bring the heat down,having it up that high...I'll drop it down to 18 inches now and see how that works out.

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who the hell told you the higher the better??!!!

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who the hell told you the higher the better??!!!

I read it off some site I found while browsing the net.

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who the hell told you the higher the better??!!!

I read it off some site I found while browsing the net.

stick to UK420 mate I found the advice I have got on here is spot on.

I am a new grower too and trying to find the optimum height for my 600w. I am same as grandad have a 9" fan on the floor and one on canopy.

good luck.

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With a 400w HPS, i found that 21" is perfect for this wattage, i have fans blowing on the ladies but anywhere from 18-24"

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