Wattage/lumens vs distance

Sirgreggins

Well-Known Member
I'm looking to start a new 600w tent grow and upon reading some threads I came across an interesting discussion. The basic premise is that wattage or lumens arent what's important here. But rather the range the light is from the plants and the coverage of light. a 400w 12" from your plants would be better than 600w 24" away as an example. The quote below has an explanation backing up this theory and I'm curious to hear others thoughts on it. My grow will be in a 48"x24"x68" tent using the SOG method. ( I want to experiment since i've grown with other techniques before)
Watts have nothing to do with light or growth. Watts measure how much power a light fixture uses to produce light. You can tell how efficient a light bulb is by looking at watts. A 23 watt CFL produces as much light as a 100 watt incandescent...even though the incandescent has more watts, it's useless. See what I mean?

What you care about is light...more specifically, light energy. That's what plants use during photosynthesis/growth. Light is measured in lumens. In my experience and reading, lumen amounts per sq. ft./sq. m. look like this

2000 lumens sq. ft./21500 lumens sq. m. = Absolute minimum for growth. You won't get much from this, especially after the plant has grown a bit. Not really enough to flower well.

3000 lumens sq. ft./32250 lumens sq. m. = Pretty Good growth. Enough light for the entire light cycle, although your yields may be lower.
4000 lumens sq. ft./43000 lumens sq. m. = Very good growth. Once you pass around 3500, growth rate and ability goes up fast.

Over 5000 lumens sq. ft./53750 lumens sq. m. = Optimal growth. Dense growth in all stages.

Keep in mind that using reflectors, using mylar or having flat white walls, and keeping your lights close to your plants keep you from wasting lumens. It's not just about having light, it's about getting the light to your plants. IMO, people ofter overbuy lights. This creates more light, but the light isn't always hitting the plants. And that creates more heat and ventilation issues, which causes stress problems.

That's why it's still impossible to tell anything about growth or yield based on just lumens. A guy that has an HPS that is too far away from plants that have no walls near them and no ventilation may get poorer results than a grower with CFLs that uses reflectors and has a couple of lights under the canopy in a well-ventilated spot.

HPS lights are often said to generate more heat than CFLs. That's not really true...it's just that they are more efficient at producing light, and there's a smaller surface area on the bulb itself for the resulting heat to dissipate. That means more ventilation. But the higher amount of lumens per watt means you use less power and get greater light penetration through your canopy. Still, I'm a believer that well used CFL's can give you great grows with less ventilation and heat issues. If you're in a small to very small area (less than 4 sq. ft./.25 sq. m.), I'd consider the advantages of CFLs in that way.

But HPS is more efficient. A typical 250 watt HPS bulb/unit will produce about 27,000 lumens. I've seen people use a 250w in a 3' x 3' room and get good results. That's 9 sq. ft. which = 3000 lumens a sq. ft. (Really, a 250w HPS is better in a smaller area.) to give you an idea of the difference in efficiency of CFL vs. HPS, think of this.

23w CFL = 1600 lumens = 69.6 lumens/watt
30w CFL = 2000 lumens = 66.7 lumens/watt
40w CFL = 2600 lumens = 66.3 lumens/watt

compared to

150w HPS = 14000 lumens = 93.3 lumens/watt
250w HPS = 28000 lumens = 50 lumens/watt

So you can see that HPS is m112 lumens/watt
400w HPS = 50000 lumens = 125 lumens/watt
600w HPS = 90000 lumens = 1ore efficient than CFL...and as you get into bigger HPS bulbs, it becomes a lot more efficient. There's also fewer hassles with multiple cords and saved money on your energy bill. If you've got a big area and/or you can deal with the heat and ventilation, HPS is the way to go in flowering. Still, I'm a believer in small HPS lights and combo HPS/CFL grows...if you've got a 2' x 2' room, you can use a 150w HPS and 4 23w CFLs from Wal-Mart and get a terrific grow with very few heat issues.
 

SupraSPL

Well-Known Member
To understand the capability of a light, a good starting point might be electrical efficiency and reflector efficiency. At this stage in the game I would not recommend anyone designing a new grow room to buy fluorescent of any kind, because of efficiency (heat) and cost.

Compact CFL ~ 25% efficient
4 foot fluoro tubes ~30%
315W ceramic metal halide ~38% efficient
600W single end HPS ~37% efficient
750W double ended HPS ~39% efficient

All of the lights mentioned above emit in 360 degrees and experience ~30% losses in the reflector, through the glass and on the wall. That energy become pure waste heat in your grow space. Because they are so dependent on the hood, as it gets dusty/filmy/foggy the reflector loses efficiency an has to be replaced regularly or else a very significant loss of intensity in the canopy. The best HPS hoods are expensive AC/DE hoods which require the extra cost, electrical draw and tubing for the inline fans.

LED emits in less than 180 degree cones and reflector loss can be reduced to less than 10%. Depending on the design, the electrical efficiency can be much higher than CFL or HID can offer.

Generic red/white/blue LED grow lamps (95% of the grow lamps on the market) ~20% efficient
High quality red/white/blue LED grow lamps (using genuine CREE/OsRAM) 35-40% efficient
Commercial COB lamps 42-51% efficient
New DIY COB lamps are commonly 56% efficient and can be designed up to 70% efficient

Commercial COB lamps don't cost much more than HID when you break it down. DIY COB lamps are about half the cost of commercial fixtures + your own labor cost.
 
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SupraSPL

Well-Known Member
The "correct" distance to canopy is the one that keeps the light off the walls as much as possible and spreads the light into the canopy as even as possible. Reflective walls are better than no walls, they do reflect a lot of the light into the canopy, but some light gets converted into heat during the bounce and a lot gets scattered bouncing multiple times. Also the walls gets dirty over time losing reflectivity. So to get the very best results, combine

-high electrical efficiency
-low reflector losses
-correct distance to canopy
-ideal intensity/photon count (700-900 PPFD?)
-uniform light spread
 
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PSUAGRO.

Well-Known Member
The grower's theory you quoted is slightly misinformed..............600w hps is the most efficient SE hid on the market. 150w hps is NOT better than a 250w hps in converting energy to light. Cfls + 250w,/400w hps combo will not beat a 600w hps @ the same wattage draw in a CONTROLLED environment...........ever.

If you can't control your heat, you picked the wrong lighting/exhaust for your specific situation


edit.............supra got this covered!, ha
 

SupraSPL

Well-Known Member
My setup is "Heatsink Armada" style hard hat work zone. Probably not the ideal setup for most growers but I am willing to sacrifice convenience if I can squeeze a bit more gpw out of it. CXB3590 3500K CD @ 25W ea, 750 PPFD, passive cooling, remote driver boards. COBs are mostly bare, a few reflectors on the outside walkways.
DSC08870b 30 CXB3590s.jpg

I have a very uneven canopy due to testing many varieties in each run, no trellis just some bending and tying branches, so the extra heatsink adjustability is helpful. But for a more user friendly setup with an even canopy you can run something like @Growmau5 This is an awesome DIY COB video

My favorite recommendation is (1) HLG-185H-C1400A with (4) CXB3070 3500K CD. 200W/bar. If you put 400W in a 4X4 you are looking at 630 PPFD averaged. If you went with 600W that would be 950 PPFD averaged when turned up to max.
 
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Rahz

Well-Known Member
A few comments to add to what's been said. Par watts matter. Lumens is a rough estimate for white light, but the spectral curve will influence the lumens/par watt ratio. Better to just go by par watts and desired spectrum.

As far as keeping the lights low to help penetration I don't see that being a major design consideration. Figure out # of emitters to be used will provide spacing. Spacing determines optimal lamp height. If the emitters are 12 inches apart the lamp should probably be used around 12 inches from the canopy. If the emitters are 8 inches apart the lamp should probably be used 8 inches from the canopy. Etc.

You could design a lamp with more emitters so it can be used closer, but when it comes to using more than 1 emitter per foot I think of height restricted areas. More than 1 per foot is a good idea but I think performance gains beyond 1 per foot will be small.
 
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