well having read all the post on floro V Hps i decided screw it and got an
eBay.co.uk: 400w POOT PL90E HPS Grow light hydroponics lamp sodium (item 250134551917 end time 01-Jul-07 10:16:42 BST)

so what distance should i keep it from my plants as i dont wanna turn them into toast!!!

currently using rack fans to keep plant temperatures at ideal temps (rack fans similar to Rackmount Net - MF-05 - Rack Fan, 1U W/3 Fans, Air Blow Up or Down) but bigger. you be amazed how cheap these are from bankrupt stock - used pc dealer etc

cheers in advance!!!

A very general rule of thumb is that your garden needs 50 watts of HID lighting per square foot of illuminated area. This rule ignores the shape of your garden, so the following is really a better guide:

A 250 watt HID will illuminate a 2' x 2' garden.
A 400 watt HID will illuminate a 3' x 3' garden.
A 600 watt HID will illuminate a 3.5' x 3.5' garden.
A 1000 watt HID will illuminate a 4' x 4' garden.

From Jackerspackle, here's a different take on watts-per-square-foot/meter (WPSF).

WPSF assumes that the bulb's intensity is equal over the entire grow area.. in other words each square foot/meter receives the same number of lumens. But in reality light diminishes rapidly the farther you go from the bulb (1/4 the intensity for each doubling of the distance). So each bulb has a limited range, beyond which you do not have good growth.

For example, a growspace that's 2 x 10 feet would require 1000 watts if you go by the 50 WPSF guideline that's commonly mentioned.. But a 1000 watt bulb only covers an area about 5 feet across - meaning the edges of your garden will be dark.. A better choice in this case would be three 400s or two 600s.

Another problem with WPSF is it assumes all bulbs have the same intensity. But 1000 watts of HPS is not the same as 1000 watts of fluorescents or (yuk) incandescents. Fluorescents have their lumens spread out over a long tube and are therefore dim.. incandescents have the wrong color spectrum and are also dim.

Nor is a 1000 HPS the same as four 250 HPSs.. 250s don't have anywhere near the intensity needed to penetrate thick canopy or tall, bushy plants. (Don't even think about growing meter-tall plants with a 250.)

I could go on, but here's a basic guideline for lighting a growspace for good growth using common HIDs:

WATTAGE -- COVERAGE
1000 watt - 4 to 5 feet across (1.3 to 1.5 meters)
600 watt - 3.5 feet (1 meter)
400 watt - 2.5 possibly 3 feet (.8 to .9 m)
250 watt - 2 feet (.6-.7 m)
175 watt - small, less than 2 feet

These numbers assume you have a good reflector around your bulb and also reflective wall coverings. You can increase the figures a bit if using multiple bulbs, due to their overlapping effect. You can also increase coverage using a light mover...

I know this won't put to rest the old WPSF idea, but i hope it shed some light on the subject. -~

What about a 5 x 2 area?

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“True heroism consists in being superior to the ills of life, in whatever shape they may challenge us to combat.” - Napoleon Bonaparte

a 400w HPS no closer than 15 inches or your plants will toast!!!!

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"5TON3D AGA1N"
peace

yes i agree i have an area 41/2 ft x 5wide, 81/2ft height ..i find that 20 to 24 " high from plant tops just right ..factoring in the outside temps being raised by my 400..temps outside our area{ being northern where i be } and being first time grower and all its great..ther all about 2" tall

I reread the post an see the HID is from Europe..it looks sweet..

I keep my 600 watter about 8-10 inches from the tops but my lights are on movers so they dont stay in 1 place to long.EAsy way is to use the hand test. place your palm at the top of the tallest planst with the back of your hand up to light lower the light til the back of your hand just starts to get uncomfortablly hot and your good. Watch the tops and adjust an inch at a time as needed for growth.Measure that original distance and you have the constant distance.Good luck

i keep my 400w mh multi spec bulb 10 inches away, no mover or inline fan, just a fan blowing on the light. wish i had it that close for the whole grow, but i ran it up and down through the grow for various newbie related reasons lol... i know my mh puts out 40k lumens, and is probably not nearly as hot as a 400w hps, though...

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cheers ~LoveIt
check out my current somango/ww grow! (and don't forget my 1st bagseed grow journal- cured and in')