How many can u grow under what???

if the measurement exists, my bad but thats my assumption.

We can it's called PAR and it can be measured and it is all about what plants actually respond to

can u help me understand then on a bases of the thread question with par watts?

"Through no small miracle, plants change the light they receive from the sun and the carbon dioxide animals exhale along with water into the chemical energy they need for growth with the oxygen we, along with millions of other species of animals, need to breath as a waste product in a process called Photosynthesis. The interaction of light and plant is a complex science involving various pigments within the plant such as chlorophyll, carotenes , and xanthophylls that reflect or absorb energy from certain wavelengths of the light they receive to maximize the photosynthesis process. Understanding the exact variables within the light source and their effects on the plant is crucial to being able to understand how to produce bigger and better plants and to maximize their numbers in traditional and artificial growing environments. PAR, or Photosynthetically Active Radiation, is the name given to the band of solar light that is useful to plants in the intake of energy and production of oxygen. This region of the solar spectrum corresponds to the portion of light that is visible to humans. Within the PAR region of the spectrum, the light is further broken down into the primary plant growth bands of blue, red, and far red." <<-- explains par a bit. but
finding ur PAR from Lumens is like converting a watermelon to a mango. Lumens is a measure of precieved power of light and PAR is Photosynthetically Active Radiation. A lumen can have 0 PAR depending on the spectrum of light it emits.
A better measurement is PPFD - Photosynthetic Photon Flux Density, which is the amount of photosynthetic available light emitted from a bulb in a defined area.


and i have 16 plants under my 1000wHPS&400wMH flowering, witch is not 100w per plant but they are doing great.
plant size/shape determine how many you can fit also.

There are 3 considerations in choosing lamps for plants, vs. lighting for the human eye: PAR, PPFD, and the duration of both. Let me explain. PAR (photosynthetically active radiation) are the violet, blue, and red wavelengths needed by the "higher" plants that most of us grow. These wavelengths appear dim our eyes even at high wattage or lumens, so "bright" lamps are an eye thing irrelevant to plants. The amount of the colours/wavelengths ROYGBIV in a lamps is revealed by its "spectral power distribution" graph (SPD). The company who makes the lamps will often fax the SPD graph to you if you cannot find it on the Internet. I've got piles of them. By keying in on your browser, "spectral power distribution of sylvania fluorescent lamps" you can see examples of what I'm talking about.

Then I compare these lamp graphs to the "absorption spectra" of plant pigments, namely chlorophyll a, chlorophyll b, and the carotenoids - particularly beta-carotene. Plant pigments will either reflect off the wavelengths that your lamps provide or will absorb them for photosynthesis. They reflect off most of the green, yellow-green, yellow, and yellow-orange wavelengths that just so happen to appear as bright to human eyes. Absorption spectra graphs reveal that violet, blue, and red (PAR) are what are needed for photosynthesis, and CRI of lamps don't indicate what colour wavelengths are in a specific tube. "Cool white" and "warm whiate" terminology is equally useless! Light intensity in watts or lumens do not refer to how much PAR is available to a plant, and is also irrelevant to how much PPFD (explained next) exists.

The measurement of how many usable photosynthetic wavelengths actually reaching the leaves (its density) is called PPFD, or photosynthetic photon flux density. This is about usable photons. And if the PPFD is not enough in your lamps when the PAR is relatively good, many plants can make up their need for a daily amount of carbohydrate production just by settin the light timer to remain on another 2-3 hours.

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600 watt HPS = 12 Plants = 9 gallons of 4 week cured bud







4 plants












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awsome explanations guys i will do a little more research with graphs etc. thanx

You're asking the wrong question. You should be asking how much area the light can cover, effectively, rather than asking how many plants you can squeeze into that space. That's up to you. For example, if you were using a 1000 watt HPS/MH to cover a 5' x 5' area,(it's approx. max area of coverage) you could have 4 big plants, or 50 smaller ones. The number of plants, is irrelevant, it's the size of the area to be covered, that's important.

jawbrodt said:

You're asking the wrong question. You should be asking how much area the light can cover, effectively, rather than asking how many plants you can squeeze into that space. That's up to you. For example, if you were using a 1000 watt HPS/MH to cover a 5' x 5' area,(it's approx. max area of coverage) you could have 4 big plants, or 50 smaller ones. The number of plants, is irrelevant, it's the size of the area to be covered, that's important.

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Very true.. guess i made it more complicated then i needed to lol.

so your saying 1000watt HPS/MH covers 5 square feet???

the next question i guess is how far away can the lights be, like for a 400watt or for one of my 1000watts??

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"so your saying 1000watt HPS/MH covers 5 square feet???"

Gibbs a good rule of thumb is 50 watts High Intensity Discharge (HPS & MH) per square foot for a stationary light. 1000 W covers 20 square feet, 4'x5'. Double the length with a light mover.

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"how far away can the lights be, like for a 400watt or for one of my 1000watts?"

About 18".

The exact measurement is how far the light has to be not to burn your plants. Put the back of your hand (more heat sensitive than the front) to the light and move it away and towards the light. The distance that you can keep your hand comfortably from the light will be around where you can keep your plants. The distance will vary depending on ventilation, air cooled or regular reflector, ambient temperature, etc.

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Hobbes said:

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"so your saying 1000watt HPS/MH covers 5 square feet???"

Gibbs a good rule of thumb is 50 watts High Intensity Discharge (HPS & MH) per square foot for a stationary light. 1000 W covers 20 square feet, 4'x5'. Double the length with a light mover.


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"how far away can the lights be, like for a 400watt or for one of my 1000watts?"

About 18".

The exact measurement is how far the light has to be not to burn your plants. Put the back of your hand (more heat sensitive than the front) to the light and move it away and towards the light. The distance that you can keep your hand comfortably from the light will be around where you can keep your plants. The distance will vary depending on ventilation, air cooled or regular reflector, ambient temperature, etc.

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so ur saying good rule of thumb is 50 watts per square foot? well then my 400watt MH can obtain 8 square feet when this other guy on this thread (too lazy to check in middle of responding) is saying 1000 watts is only good for 5 square feet.

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This one Gibbs?

by Jaybrodt, post #28
"For example, if you were using a 1000 watt HPS/MH to cover a 5' x 5' area,(it's approx. max area of coverage) you could have 4 big plants, or 50 smaller ones. The number of plants, is irrelevant, it's the size of the area to be covered, that's important."

You may have read it quickly. 25' square.

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another thing i havent seen mentioned, your reflector determines the light distribution also. with a bat-wing reflector i was getting approx 5' square. now, with a 4 foot parabolic dome reflector im getting approx 10(might be more but it goes wall to wall)
just saying, lol

yes hobbes, thanx. and ya def. a factor jumbo. i have a baseup dome reflector for my 400watt MH ( mayb same as yours, havent herd that term or name tho "parabolic") and just horizontal refectors for my 1000watts..

yea they probably are the same, "parabolic" actually comes from how it is made structurally, coming from the word parabola = a conic section formed by the intersection of a cone by a plane parallel to its side. basically fancy talk for a pain in the ass to assemble dome =] haha

jumboSWISHER said:

yea they probably are the same, "parabolic" actually comes from how it is made structurally, coming from the word parabola = a conic section formed by the intersection of a cone by a plane parallel to its side. basically fancy talk for a pain in the ass to assemble dome =] haha

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haha ya i saw ur pics, looks like a pretty effective reflector man! but i intend to upgrade the one for my 1000 watt HPS, then mayb the MH.. but my 400s good growin quite a bit under it