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Jackerspackle's Lighting Coverage Primer

SmokeyMacPot

New Member
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.

Author: Bongaloid
 

MrWeeds989

New Member
by:SmokeyMacPot
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

THANK YOU for posting this!!:nicethread:

my flower room is 7ft x 11ft (2m x 3m i think. I stink at most conversions) and I had the impression that I NEEDED to put 4 1000w lights in there.

so 2 1k lights should do the trick? Aside from the extra advantages of having 4 1k'ers in there, my heat problems would be severely diminished. Recently I have decided to add LED Red & Blue as side lighting, and using 3 1k'ers.

Basically I am trying to get the max light in my room with the least amount of heat, as I assume we all do? lol

thanx for this post, it definitely got my brain churnin, and crunching numbers.:thumb:

edit: my Veg area is 3ft by 4ft and i use a 400w hps would a MH conversion or an HPS w/Blue be better? I also just noticed when this thread was started, :/
 

Excited2start

New Member
Puzzu an HPS bulb is a HID bulb. HID stands for High Intensity Discharge and an HPS bulb falls into that category. If you were going to choose a bulb I would suggest a MH (Metal Halide) bulb for flowering as they are more in the blue spectrum of light which is good for veg. growth. While for flowering I would suggest an HPS(High Pressure Sodium) bulb which is more in the red spectrum and usually have a higher amount of Lumens as well. Now you can go through a whole grow with either type of HID bulb just better if you use them both. There is also plenty of information on this site that can really help you choose the best type of light for your situation. hope this helps and good luck.
 

Hogdady

Plant of the Month: June 2010 - Nug of the Month: July 2010

TorturedSoul

Member of the Month: May 2009, Oct 2010, Sept 2017
So a 40w tube rated at 2550 lumens is spread over the entire 4ft length? Not 2550L per sqft?

Old post, but for anyone reading this and wondering: Yes, tube lights have their output spread across the entire tube. But one generally has a lot more than one tube in a setup. 8 4' 3,000 lumen tubes crammed into a 1' x 4' area produce 24,000 lumen - or 6,000 lumen per square foot. (Not all of which will be usable, of course.)
 

trigger-420

New Member
how much wattage would you need if you were using CFL's? am i correct in assuming 40W per sqr foot, or is it per area?
 

DontEvenAsk

New Member
So 1000w per 4x4? I kind of did the math and came up with.. My room being 16 x 9 x 10 Length Width Height... 6 lights MAX in there, but 4 at first to be safe.. my question is, would six 4x8 tray stands be fine with 8 plants per light?
 

TorturedSoul

Member of the Month: May 2009, Oct 2010, Sept 2017
So 1000w per 4x4?

Well, that's 62½ watts per square foot. That'll work well for most strains, and you should even be able to grow equatorial sativas (although they might want more light for best results).

I kind of did the math and came up with.. My room being 16 x 9 x 10 Length Width Height... 6 lights MAX in there, but 4 at first to be safe.

When placing multiple lights in one room, you tend to get a "third light effect" between them, which basically means that... Err... Light output drops off near the edges of a light's footprint, yes? So if they're placed properly, the "drop-off areas" of two or more lights can actually have enough light (when combined) to be significant. If that makes sense, lol. There's a better way to state it, but I seem to be lacking coffee today, so...

Also, 600-watt HPS are more efficient - in terms of output per watt - than 1,000-watt ones. The 600-watt HPS' ability to penetrate into a canopy is somewhat less, but still pretty good. When dealing with larger spaces where you'd end up using multiple light sources regardless of their wattage, it might be worth considering 600-watt ones. If the additional expense of purchasing more lights is not an issue, of course. Also, with more lights... You might decide to mix your spectrum / bulb type, maybe add in up to 25% metal halide.

There is no requirement that all of your lights must be the same wattage, BtW. So you have quite a few options.

my question is, would six 4x8 tray stands be fine with 8 plants per light?

It's probably not what you want to hear (err... read), but I always say to fill your grow space with an adequate amount of light for the size of the space, and the decision of how many plants to put into that space is up to the grower. I've seen plants in a sog (sea of green) grow spaced at nine per square foot - and I once saw pictures of a single-plant grow with around 10,000 watts of HID lighting (think "tree," lol). I believe the single-plant grow was in Australia. I do remember that it was somewhere that the potential penalties (of getting caught by LEO) were largely determined by the number of the plants, not size or weight. Talk about taking advantage of a technicality, lofl.

But, really, illuminate your grow room enough that there are no dim spots, shadowy corners, et cetera. Then determine the number of plants based on things like your preferred growing method/style, how long you want to have them in the vegetative phase (when longer, you tend to get larger plants, of course), strain choice and your strain(s) particular growth characteristics, et cetera. Your own size may effect the number of plants you wish to grow, lol - if you weigh 550 pounds, you'll need some space of your own whilst working in there ;) . If you have ensured that your entire grow space is as bright as can be, as opposed to trying to figure out how much light per plant, you'll probably have a better grow and one that gives you more options (which, again, will tend to give you a better grow - and a more enjoyable one).
 

DontEvenAsk

New Member
Well, that's 62½ watts per square foot. That'll work well for most strains, and you should even be able to grow equatorial sativas (although they might want more light for best results).



When placing multiple lights in one room, you tend to get a "third light effect" between them, which basically means that... Err... Light output drops off near the edges of a light's footprint, yes? So if they're placed properly, the "drop-off areas" of two or more lights can actually have enough light (when combined) to be significant. If that makes sense, lol. There's a better way to state it, but I seem to be lacking coffee today, so...

Also, 600-watt HPS are more efficient - in terms of output per watt - than 1,000-watt ones. The 600-watt HPS' ability to penetrate into a canopy is somewhat less, but still pretty good. When dealing with larger spaces where you'd end up using multiple light sources regardless of their wattage, it might be worth considering 600-watt ones. If the additional expense of purchasing more lights is not an issue, of course. Also, with more lights... You might decide to mix your spectrum / bulb type, maybe add in up to 25% metal halide.

There is no requirement that all of your lights must be the same wattage, BtW. So you have quite a few options.



It's probably not what you want to hear (err... read), but I always say to fill your grow space with an adequate amount of light for the size of the space, and the decision of how many plants to put into that space is up to the grower. I've seen plants in a sog (sea of green) grow spaced at nine per square foot - and I once saw pictures of a single-plant grow with around 10,000 watts of HID lighting (think "tree," lol). I believe the single-plant grow was in Australia. I do remember that it was somewhere that the potential penalties (of getting caught by LEO) were largely determined by the number of the plants, not size or weight. Talk about taking advantage of a technicality, lofl.

But, really, illuminate your grow room enough that there are no dim spots, shadowy corners, et cetera. Then determine the number of plants based on things like your preferred growing method/style, how long you want to have them in the vegetative phase (when longer, you tend to get larger plants, of course), strain choice and your strain(s) particular growth characteristics, et cetera. Your own size may effect the number of plants you wish to grow, lol - if you weigh 550 pounds, you'll need some space of your own whilst working in there ;) . If you have ensured that your entire grow space is as bright as can be, as opposed to trying to figure out how much light per plant, you'll probably have a better grow and one that gives you more options (which, again, will tend to give you a better grow - and a more enjoyable one).


Thanks for this very insightful answer. :) +1repped! I was just trying to figure out my layout before I start since I only have this one room for both veg and flowering so this does help a lot.
 
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