Watts/lumens per square foot ?

[whazzup]

btw I meant 43 mol/m2 per day of course ;)

 

[Crysmatic]

thank you! Are you saying I'll overload my plants having the lights parallel? I'd like to think that I'll have a nice, uniform plateau over the majority of my canopy.

I'm visiting with a greenhouse owner next week, and I need to speak in his terms. what is 43 mol/m2 in W/m2 or J/cm2? It's obvious to me that 1000 umol/m2/s is at 60 cm from the bulb. the bottom of the plant will receive much less under the HPS. Solar irradiance is constant. That's why I asked for *average* irradiance. So...if we have 1000 umol/m2/s at 60 cm, what is the irradiance at 75-80 cm? (assuming 1.2m tall plants, and 90 cm of canopy "thickness")

mol is a measure of photons, while Joules is energy...which is related to the PAR spectrum specific to the Phillips' EL HPS.

from plant physiology online:
"How much light is there on a sunny day and what is the relationship between PAR irradiance and PAR fluence rate? Under direct sunlight, PAR irradiance and fluence rate are both about 2000 µmol m–2 s–1, though higher values can be measured at high altitudes. The corresponding value in energy units is about 400 W m–2."

 

[whazzup]

As you already say, you can't even see the uniformity because there is so much light. Your eyes are bad instruments for this high intensity. To see if you have enough room for your lamps the calculation is pretty simple: take the PPF you have and divide by the surface, subtract in a small room 10-15% for wall losses. That doesn't tell you yet how to hang the fixtures to get uniformity but you get a pretty good idea. So for example 2 fixtures of 2000 umol @ 100% = 4000 umol. On 3 m2 that is average 1333 umol -15% >1100 umol so really more than enough.

About the heat: An empty room is always warmer than a room filled with plants. They cool the room considerably by their evaporation.

Irradiance further from the lamps depends on the overlap and the distance of the lamps. Growers use micromoles over wattage as it is the number of photons that relate to the potential photosynthesis, not the wattage, when the spectrum is sufficient.

Overlapping lamps assure high irradiance values deep in the crop. This is one of the qualities of the HR96, as it is deep, but also has a wide spread to be able to create this uniformity. Light levels and patterns on different distances are different.

Blue photons contain more energy than red photons so indeed you can not just translate micromoles to W/m2, that depends on the spectrum. We never work with W/m2, just with micromoles. Greenhouse growers use mol/m2/d as well. I suggest you read the Purdue University document about DLI again.

About the sunlight: fortunately the sun isn't 2000 umol s-1 m-2 constantly. DLI is a better measurement to see how much light you really have per day cycle, but you shouldn't go close to saturation levels.

 

[whazzup]

oh, ideal measurements for a 1x1000W lamp are 1.2x1.8, 2.5m high, lamp at 2.3m.

avg light levels with uniformity over 85% at:

0.9m - 739 umol
1.1m - 820 umol
1.3m - 904 umol
1.4m - 950 umol
1.5m - 1009 umol

Then double the room to 2.4x1.8 and add a fixture. You now have less wall per fixture, so higher light levels, which show as follows::

0.9m - 810umol +71
1.1m - 869umol + 59
1.3m - 940umol + 36
1.4m - 987umol + 37
1.5m - 1036umol + 27

So you see by these figures the depreciation of light is less than with a single fixture.

 

[ttystikk]

Thanks for the hard data, as always, Whazzap- appreciated in so many ways!

'So you see by these figures the depreciation of light is less than with a single fixture.' Do I take this to confirm my intuition that having several lights in an array tend to reduce the effects of the inverse square law in light pressure? And that the more units in the array, the more pronounced this effect?

 

[ttystikk]

oh, ideal measurements for a 1x1000W lamp are 1.2x1.8, 2.5m high, lamp at 2.3m.

avg light levels with uniformity over 85% at:

0.9m - 739 umol
1.1m - 820 umol
1.3m - 904 umol
1.4m - 950 umol
1.5m - 1009 umol

Then double the room to 2.4x1.8 and add a fixture. You now have less wall per fixture, so higher light levels, which show as follows::

0.9m - 810umol +71
1.1m - 869umol + 59
1.3m - 940umol + 36
1.4m - 987umol + 37
1.5m - 1036umol + 27

So you see by these figures the depreciation of light is less than with a single fixture.

One more, rather specific question; I am seriously considering a lighting upgrade to Gavita 1000DE technology. Would you recommend swapping these in for conventional 1kW lighting on a one-for-one basis, or would that be overkill or even detrimental? I'm currently running 4x1000w Magnum xxxl 8" 'ocho' hoods in an 8'x8' (2.5m x 2.5m) space. To get the most out of them, I plan to run them at the 1150w setting most of the time. This would be the rough equivalent of the 1kW bulb and magnetic ballast, so I'm not anticipating my power consumption to change much.

 

[whazzup]

inverse square law: forget it. You are using a lamp with a reflector, not a point source. Inverse square law starts to work as 5 times the maximum length of the source, assuming that it radiates uniformly, which a lamp in a reflector doesn't. Try applying ISL on CFL's or lasers or make calculations based on ISL and apply them to my example.

Please read my calculation again. 4xpro 1000@ 1150W = 4x 2300 umol=9200 umol

Surface is 6.25 m2. ppfd average would be over 1400 umol, way too much! Also you would need at least 80-90 cm distance from your crop at this small space to prevent peaks of well over 1500 umol. I assume that you are now using air cooled 1000W, which (with the best lamp you can get on the market) output about 35-40% less than you would get with a Pro 1000 @ 115%. If you use magnetic ballasts now chance is that you will do this with the same electricity use for the lamps. You would never get away with this amount of light without airco.

It is the trick that you balance the output of the lamp to the surface to get about 1000 umol s-1 m-2, also taking the height of your room into account as you want to overlap. So 4x1000W in a 3x3m room will give you average about 800 umol s-1 m-2, but with a not so good uniformity. 8x600W would be a much better option in a 3x3 tent when it comes to uniformity (90% instead of 55%), light peaks, heat distribution and maximum height of your crop. You would reach 1000 umol s-1 m-2 and would be able to grow your crop about 20-30 higher. at 50 cm you would have still well over 700 umol s-1 m-2 ith the 8x600W solution. With the 4 x 1000W that would be about 620.

The problem with the 1000W solution is that when the plants come closer to the lamp they will be over-saturated and you don't have enough sources to spread the light evenly on that surface and can't get close enough to the lamp.

 

[ttystikk]

So I should NOT get the 1000DE lights? The ceiling is 2.5m high, so I have the vertical room to install the lights as much as 120cm above the canopy. The canopy area is 2.5 m square, substantially less than 3m. Would this result in sufficient uniformity? Should I light 3m square anyway?

I actively manage canopy height and density by using a horizontal trellis, thus there will be no plants growing too close to the lights.

 

[whazzup]

My point is that you would use too much of a good thing on this surface. and you would over-saturate your plants.

If you want to use 4 lights then use 2.4 x 3.6m and get more than 900 umol average @ 1.4m with a uniformity of 90% using the fixtures @ 100%. @1.7 m you have about 1000 umol average but with a lower uniformity. However, peak intensities will be much lower (~1300 umol straight under the lamp)

See what goes wrong with your setup I illustrated in the attachment

 

[whazzup]

probably posted this here somewhere but this is how efficient it is to use high light levels. You can see that the optimum is way under 1500 and that 1500 can be regarded as the saturation level. going from 500-1000 gives you much better roi than going from 1000 than 1500. Also see what temperature does to efficiency (also good information for the LED growers!!)

 

[purpleberry]

Replacing 4 xxxl hoods with gavitas would be a mistake, There not going to cover that same 8x8 good. All this lab data is not real world test, You have to hang light and see what happens. Ive dont it with 1 light 2x now. The first time against air cooled xxxl and it yeilded the same. This time against open bulb agrotech xxxls. Half the room was xxxl and other half mixed with odd ball hoods. The entire side xxxl is alot larger and turned color alot faster from using up more fert from the extra light those hoods put. Ive never seen such a difference down the middle of a room.If you put on some blue sun glasses you can see the whole side of the room is brighter and very uniform in light compaired to the other side. The gavita got stuck in the corner, You can see it dont cover for shit and it isnt as bright as the xxxls.
I dont think its the DE bulb, Its the crapy hoods. You put up all the charts and tech info you want it ist going to make that hood work any better, IM not saying it cant work good when you hang multiple at the right spacing, I can see how good the light reflects withthe reflector that close, It just puts out s 2.5x3.5 foot print. Im saying 4 xxxls over 8x8 is going to kick ass over 4 gavitas imho
I wanted to do the room half gavits in xxxl DE hoods but sunlight keept telling me they would have me the hoods and they probally still dont, Now i already bought lumatecs so that isnt going to happen any time soon. Maybe able to do a couple

 

[whazzup]

You will never see a difference in a room, period, I would say. Your eyes are not capable of seeing such a difference at that intensity. Also look at the scale, that is a very small scale, going from 20-100 umol per colorsegment. A 90% uniformity is really not bad at all. On ICmag you can see a good topic about some measurements members did about the spread and uniformity of several reflectors. That's a recommended read if you think the HR96 is a crappy hood ;).

Also take into account that I made this calculation to illustrate why it would not work.

I would really recommend you to do a few measurements in your room to see what the actual uniformity is. Take them at different heights at a square pattern and map them like in the reflector topic on icmag. Then see how deep your reflectors really are and what the light maintenance is, going deep into the crop. It can be a really an enlighting experience.

I don't only base my recommendations on what I calculate, but also on the results that people or companies who follow these recommendations obtain by using them. I don't guess or base my recommendations on anecdotal evidence. You will see that light calculations are in real life pretty accurate. In horticulture ppfd and uniformity is something we have to guarantee when making a proposal. The diagram about photosynthetic efficiency of light I showed you is not based on theory, but on published scientific research on cannabis sativa plants.

I would not recommend the 4 pro 1000 on this surface as it would be too much light, as I showed in the published document. If 4 other 1000W lamps would not be too much light on that surface imho says more about the efficiency of the Gavita reflector and the philips lamp.

 

[purpleberry]

If you put on blue shades you see alot in a room and i can see how well hoods cover a area, and I did take my light meter and measure different spots under the hoods, That how i figured out the gavits hood wasnt going to work in my 4x4 areas, I actually use 4.5x4.5 with multiple xxxls. The half of room with mixed hoods has alot of dead spots you can see, The xxxls side is brighter and well covered. Im sure gavits work killer if you hand them spaced 3x4 or 3x5 but i live in a 4x4 world. LOL
Saying 4 gavits over 8x8 is to much light is funny. Why would it be to much light? Move them up a little if going to burn them otherwise increase temp and C02 and they will use the light. I never seen a plant get to much light unless it burns, I hung one small hydrofarm little non aircooled square hood, i got for free, It put down a nice 2' circle The out side edges did ok but the buds in the circle are the biggest in the room and one about 20" from the bulb is HUGE I had to turn the plant about 7 weeks because the tip started to burn a little. You cant over saturate plants with light with 4K over 8x8 no way.

 

[whazzup]

well, fortunately we can agree to disagree. But I am really interested in the ppfd measurements under your hoods in that 8x8 area with the distances.

I think you would agree that adding another 1000W lamp would be a bit much on that surface? Because basically that is what you do when you exchange your 4 air cooled reflectors with Gavita Pro 1000 open reflectors:

Reflector output of an air cooled Hortilux I estimate at 1600 umol max, calculating high with 95% reflector efficiency (which is very high) and only 6% filter losses (which is very low), while a Pro 1000 fixture outputs 2000 umol. So replacing 4 with Gavita fixtures will get you a free 1000W extra lamp, including electricity costs, lamp replacement etc etc. . I'm sure you will agree that you need about 25% more space for an extra fixture.

At 825W the Pro 1000 still delivers avg 1050 umol s-1 m-2 at that surface (with a much better uniformity!), which I consider a really good amount to grow.

 

[whazzup]

btw uniformity is overrated, but bad overall uniformity can be a problem. If you see some hang their lamps ;)

 

[El Cerebro]

whazzup, your generosity and open-ness in discussing hard-earned, professional-level application data is unusual and unexpected here. many thanks.

 

[montanamike1]

I run a room of (4) 1,000w, each light covering it's own 4x4 table with 2-4 LST'd plants each, averaging .5-.75 grams per watt. Now I'm wondering if the yield increase is enough to justify electrical cost and heat...

 

[whazzup]

1000W on 4x4 should be imho overkill. But at very high light levels it is harder to obtain a gram per watt than with lower intensities and a bit bigger room. So if you would know your light intensity you would be able to make that decision. Buy a micromol meter, even a cheap one will give you an ok direction. When you have average light levels of 1300 and above, I assure you that you will get a better yield on a bit bigger surface. So that might be your first optimization which would cost you not a lot to do... other than to make your room bigger ;)

I'm not familiar with your room or your growing style so I would not be able to comment anything sensible other than this: Replacing with the same wattage Gavita would not work, your room would be too small, light levels would be too high.

 

[ttystikk]

MANY thanks, Whazzap- this is sending me off on another round of personal research- it is much appreciated to be sent in the right direction, at least!

 

[whazzup]

my pleasure :)