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lighting

Sort of depends on how you use them. Two 300W lights angled to give coverage to a single area/plant would be about equivalent to a 600W over that same area/plant but if they're hung side by side then you have less light over a bigger light footprint than you would with just the 600W. Many light manufacturers provide coverage maps for their light's footprint. A lot of people opt for multiple smaller light as it gives them more flexibility to adjust height from the canopy.

What sort of lights specifically?
GWE proposes a sweet spot of about 150W per plant. So two plants under one 300W should get about the same amount of light each as 4 plants beneath a 600W.

To get things exact you really need a light meter, ideally a PAR meter rather than a lux meter (but the latter will work depending on the spectrum of your lights.
 
Do u know if they are true 300watt draws as well all led company's wil tell u the full capablity of the lights but the lights don't actualy draw that power that being said I have 3 leds 1200w 1000w and 600w now the true draw wattage is 350w 200w 100w. So if ur 300watt leds are true watts that's a different story but u also gotta think that each fan will take about 10watts. Also leds are desighned to only point straight down just like beach said it depends on the angle and how they are used. Also my true 350wat led I also keep 6inchs away from my plants thro veg to flower seedlings I keep it at 10inch. I hope this helps
 
With leds u need to find the par value that's how ur gunna find ur useable light for ur plants and this is the equalition to find that 60x60 equals 3600 times that by the numbert of hours ur lights on (for example 24h) 3600x24eql 86400times ur par value equals(_) then devide by 1000000 this number will equal ur usuable light par. U want between 100-200par 200par is roughly 1000watt hps
 
tyler_ hobbyist said:
Also my true 350wat led I also keep 6inchs away from my plants thro veg to flower seedlings I keep it at 10inch.
Click to expand...

I find this very confusing. I have been keeping my 136 true watt LED much further away than this for fear of burning my plants. More like 18". This is what is recommended in the article here on GWE. Although NebulaHaze does in a spot or two mention 12 to 18", most everywhere else in the article, she says 18" to 24"

Obviously, if you're having success as close as 6" away with an LED more than twice as powerful as mine, it may explain the lousy results I'm getting. My LED is using 5W 90 degree lights. Does that influence minimum distances?

cheers
 
Mine also uses 5w 90degree chips. But for leds u need to figure out ur true par value to find out how far/close to keep ur light. Not all leds are made the same and all have different par rateings. Distance on the form is a general guidline. Do u know how to find ur true par value? U want 100-200 true par per day on average 200 true par would be a 1000watt hps at 25inchs
 
Haven't purchased a meter yet. It's on the list. For the time being, I'm trusting the manufacturer's specs to give me an approximate number. I'm using the specs they give here for the calculations.

At 18" - they say 480 umol per sq metre per second I'm running 136 real watts 18 hours a day or 64,800 seconds . I thought I knew the formula. But, I'm not so sure now.

I'm also using 2 to 3 (46 to 69 real watts) per plant of CFL's to get at the lower sections. But it is really just the LED I'm trying to do the math for.

thanks
 
How well your lights are made makes a huge difference in the quality of the light that your plants receive. You can not apply the information from one manfacturer to another. Weak LED lights can be much closer then a stronger one. If I took my lights any closer then 15 inches, I got burnt plants. You need to play with your lights to see where the sweet spot is.
 
60x60equal 3600x 18h equal64800x 480 equals 31104000 devide into 1000000 equals 31moles of light. Which is very low u want 100-200moles per day
 
I run viparspectra and GalaxyHydro in separate tents. I can't put mine any closer than 18" from the top of the canopy without getting some light bleaching. Every light will be different but this is my experience with these two brands.
 
where do you get the 100-200 moles daily light integral figure?

Sunlight generally doesn't go above 60 and greenhouses don't really get above 30.

According to high times (only 16 months ago), evidence points to the saturation point of cannabis to be 25 mol per square metre per day without CO2 enrichment.
 
As already said, manufacturers provide different quality and design that are mostly incomparable to eachother.
What tyler is referring to is called the daily light integral, its the total daily amount of photon energy over the PAR range. PAR is not a metric unit but a unit set. PPFD is the metric system measured in umols that uses PAR to define its testing parameters.
With cannabis, the max DLI a plant can receive before co2 supplementation, is around 40-45 mols a day. This is about 1000umols @ 12h light schedule.
In nature plants will typically not receive more than 60 mols.
DLI-maps.jpg

When supplementing with co2, plants can be pushed to their genetic potential of about 65 max DLI.
If a plant receives more light than it can handle, a plant will go into what is called photoprotection. This is where a plants photosynthesis rate is slowed to protect itself. If too much light is provided, a plant will eventually result in photodamage where dangerous reactive oxygen species occur, causing cascade damage to the photosystem centers. This is called photoinhibition.
Even when all limiting factors such as co2, light and water are adequate, the plant still has a limit on its photosynthetic rate.
Even if a plant can receive more light, it may not be utilizing it efficiently and could cause a plant to use photoprotection.
Here is a rundown on light metric systems.
http://forum.growweedeasy.com/forum/...metric-systems
 
I've had a look through the pdf and it does explain maximum photosynthetic rates in relation to light intensity, but there's no mention of daily light intergral which takes light duration into consideration as well.
 
Obviously the study does not conform to all variables to answer everything. Doing so would require a much larger, more time consuming, more expensive study. However, for the most part, i would expect photo flux density study over short term should be sufficient to surmise a conclusion. Daily light integral is a total calculation from PPFD. So you can use the ppfd to calculate the DLI. I do admit though it does leave doubt on how long term integrals would effect the maximum photosynthetic capacity. However, as he cited. Plant leaves reach a steady state after a certain amount of time. Which he applied.
Theres also the issue of the light used, being very narrow. Also strains. But its the best we have. He did revisit the test with more strains and funnily enough came to slightly different results.
 
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You know i read that article you linked and their cited anecdotal evidence mentions nothing about cannabis. Although it mentions other plant species, its not directly related. Many plants have different capacity for available light.
Did i miss it ?
 
There's a lot of info in the chart an PDF. If I've read it right, with the added PAR of my 2 to 3 CFL's per plant, I'm likely providing a good amout of daily light.

Of course, I haven't allowed for all the CO2 I keep exhaling on my plants while sitting in front of them for hours a day. :)
 
Just move it closer everyday until she tells you to stop. There's so many LED lights out there and none will be the same.
 
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