The volume of effectively illumiated plant material can be significantly greater hanging bulbs vertically with no reflector than hanigng bulbs horizontally. Yes when using a horizontal reflector the 3x3x2 area does get brighter light because of the reflector but a vertically hanging bulb generates a much greater area of ideal light.

With Horirzontal light of 400 Ws you get an area of 3x3 about 2 feet deep of useable light since you have to keep the plants 1-2 feet away depending if you are doing air cooled. So the overall area of ideal useable light is 3x3x2 = 18 sqr ft.

Vertically you can put the plants closer to the light up to as close as 6" The best light is generated directly at the level of the reaction producing light and directly out perpendictar to the length of the bulb. This generates of field of ideal light in a circular fasion 3-4' out from the bulb.
So the volume of ideal usebale light(Pi x raidus(squared)x height) is 3.14x3x3x3 -3.14x.5x.5x2 = 92- 17 = 75

This area is 4x greater than produced from the horizontal light.

In addition to this vertical lighting has more benefits if you have many lights...In a 5 light setup with vertically hanging bubs 5-8 feet apart, the plants in the middle are getting useable light from up to all 5 lights, where all the light with horizontal is directed toward the floor barely helping the neighboring plants... You go into one room with four 400 mhs and 3 600 hps vertically hanging in 2 rows and it is a big light orgie. I would say vertically hanging bulbs project useable light for up to 10 feet. Its best light is definately 3 feet away and closer up even 20 feet away the light is bright to the human eye...

I have an ideal flowering setup where I use vertically hanging bulbs to flower 2 fases of plants at the same time.
I put 6 fresh out of veg plants directly under the vertically hanging bulbs...then put 4 week old plants that had been under the bulb into new 1 foot taller pots that I place surroudning the fresh into flower plants directly under the bulb. The bulb is hung to be 6" away from the new plants while the canopy of the 4 week old plants form a spherical wall of buds around the bulb.

In this way I use the very effective light emitted directly under the vertically hanging bulb to flower the smaller plants while the most effective and ideal light projected from the bulb is used to illuminate the colas of the 4 week into flower plants.

The six 4-week-old plants form an omega garden type of canopy as close as 6" away from the veritcally hanging bulb, with the top of the bulb hanging at or below the canopy 6"+ above the newly flowering plants.
With this method depending on strain is easy to pull 1 pound per 400 Watt light every 4 weeks instead of the every 2 months of horizontal lighting, and now you can understand why. You almost use the bulb in 360 degrees while horizontal reflectors use more like 90 degrees.
Switch from the 2d to the 3d with vertically hanigng bulbs !!!

got any pics to better explain your set up ? i use envirolites and i have two hanging in amongst the plants vertically and a bigger 250w over the top , only draw back is im constantly burning leaves on the verticaly hung bulbs , i was thinking about building a diy cage out of mesh or something ,that wraps around the bulbs to stop the leaves touching the lights .

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i saw a utube vid where they did a side by side comparison of using vertically hung bulbs vs. using vertically hung bulbs with reflectors (to reflect more light 'toward the floor') the plants under bulbs without reflectors were only 2/3's as large, if even that. reflectors kick azz. there is a reason why experienced growers use them. vertically hung bulbs w/o reflectors might be suitable for growing a few large spaced apart plants. but it is not suitable for a Sea of Green where the plants are positioned closely together and are even height. in this setup there is not waste of light 'going toward the floor' because the floor isn't even visible !

I would agree that vertically hanging bulbs with reflectors is better than no reflector... but my argument here is that horizontal bulbs in reflectors are many times less efficient in illumating a volume. Thats not say that the 3x3-5x5 pattern created by the reflector is not more intense because in many cases it is...and its not say that the horizontal hung above the plants is not a better orientation than the vertical reflector. Perhaps even the reflector is needed to push the lumen intensity up to an effective level...My testing has not yet been completed.

My main point is that the vertically hanging bulb generates a field of useable ideal just short of 360 degrees 3 ft away from the bulb, where the horizontal generates a plane of light directly below it...As far as effiency goes would you rather illuminate 18 cubic feet plan or 75 cubic feet field? Not to mention the extremem benefits are neighboring light that is not present with horizontal.

There is a serious lack of information on these comparisons. I have seen the THSeeds grow video where they make a 5 second mention that reflectors are very important and they outperform vertically hanging bulbs...but I think they aren't using the light effectively...

Good Day

You guys want proof of how efficient vertical lights can be check out a grow by a guy who did it with the critical mass strain. It will blow you away and he has tons of pictures in stages. That dude has mad skillz.

Awesome grow.

Critical Mass tree grow x 2

Difficult to say whether it's better or not without a side by side comparison. I mean, the guy was using 3 x 600w lights for two plants. You would expect some dramatic results.

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Let me show you how I do it

I have an unused bulb hanging in flower.

I put 6 fresh 1-2 ft tall plants of the same strain into flower directly under the bulb as close to 6" away as possible. Here the plants sit for 4 weeks (since this strain flowers in 8 weeks) streching toward the light 6"-1' away. Then at 4 weeks I transplant these babies into a pot that is about 1 foot taller, and bring in a new set up 6 plants that will replace the ones just repotted. I put the 6 new plants as before directly under the vertically hanging bulb while the newly repotted 4 week old flowering plants form a barrier around the 6 new ones being 1-2 feet taller at this point. The top of vertically haning bulb is below or at the tops of the colas.

This light effiency is the equivalent of having an omega garden with an additional side enclosed...the only thing more effienct would be enclosing the bulb in a complete sphere...but the light projected up from the bulb is the least concentrated of any direction. A reflector would help this setup but I am not a fan of the clunky 4' vertical reflectors but perhaps I may try some experiments with turkey pans via advice BOG gave on overgrow many years ago...

Interesting post. Well thought out.
Math is always neat and fun, but I would want to see a side by side study with a final comparison between yield with vertical and yield with horizontal (with reflectors) before trying it.

Take physics, learn the inverse rule for light.

Doesn't matter how you hang them. Is the light projecting into usable areas? That's the question.

Hort. Sci. teacher, ending class.

Exactly you can ultimatly look at the plant to tell how much light they are getting.

I must admit I use horizontal reflectors in veg and the leaves do appear to be brighter even with the light being 18" away...with air cooled and the plants only 10" away I am sure this effect is even magnified for terrific growth...

But at the same time I think we all have an obligation to use the bulb to its highest effectiveness. We are all wasting 400 600 or 1k+ energy to run these stupid things with the sun right outisde...kinda sad.

So we need to make the most out of each bulb. With a horizontal you are gonna be illuminating a 3x3-5x5 area for 2 months. You are very restricted to what you can do with this space and its best just to only use it maximized for the end of the plants life.

With my vertical system the crop time per light is doubled since you get crops every 4 weeks...maybe the light isnt as bright but I can tell visibily that the plants are getting effective lights from the way they look and their growth.

With a yielding strain its easy to 3-6 ozs per plant with doing this 6 plant rotation...so a minimum you get a lb per bulb per month with no probelms...and like I said the majority of the plants get useale light from multiple bulbs so the growth is actually really incredible...

Now I agree that a horizontal reflector is better to light up a 3x3 area but as far as many light systems vertical lighting used in the right way is many times more efficient relative in Yield / electricty use.