LED square foot cabinet coverage

[eHuman]

With the Advent of LED lighting, the ever innovating improvements such as a wide spectrum of LED colors within a given Hood, reflectors, and higher wattage LEDs, it is no longer easy to determine the coverage a given light will yield an Optimum growth.

I plan on using a single chamber from seedling through growth flower and harvest.

So in determining if a given fixture will suit my needs for a 2 foot by 3 foot by 5 foot cabinet, what should I be looking for in the fixture? Lux? Lemons? Par?

If going by wattage only, a given 600 watt fixture that only draws 120 watts actual would not be sufficient for 6 square feet. An 800 watt fixture that draws 160 Watts still would not be sufficient. But I've seen similar fixtures cover larger areas and yield great results.

So what information and fixed your specifications should I be looking at to determine what size fixture of a given brand that will be sufficient for my needs?

 

[Scientific]

it is no longer easy to determine the coverage a given light will yield an Optimum growth.

You've got that right! Lighting is evolving so fast that it's hard to know what to buy and how to compare.

I posted a couple blog entries with articles that I found helpful in trying to wrap my head around what's what. Maybe they'll help?

 

[ConstantGreen]

The only measurement you should be concerned with is PPFD and the light's physical dimensions. PAR, "Photosynthetic Active Radiation" is just defining the range of the light spectrum used by plants and is measured by PPFD, "Photosynthetic Photon Flux Density". PAR meters count the amount of photons hitting the sensor per second, and you can move the sensor around your tent to see exactly how many photons a light is giving and a plant is getting in different areas of your footprint. You can plot these measurements into a PPFD chart, giving a numerical representation of the performance of the LED at different heights and footprints.

LED's specifically do not spread out light very well. Say an LED fixture is 12" square. Even if that fixture is 800w of the latest LED tech with the largest LED lens angles of 120 degrees, the effective footprint is going to be about 6" in every direction of the LED fixture's dimensions, or about 2x2'. Wider than 6" and your PPFD drops off dramatically; it doesn't matter if you're using cobs, cree, quantum, mars, DIY or some other LED tech. Ignore everything you read about a light being equal to XXX watts of HPS, it doesn't help you decide anything. HPS bulbs cast light in nearly 360 degrees and need to be put in a reflector to concentrate the light onto the footprint. HPS bulbs in a reflector also have the same problems of not being able to spread light wider than 6" or so.

The innovation with LED is that you no longer need to contain a hot, gaseous ball of light in a reflector. LED's are tiny and hundreds of them make up 1 LED grow light. This means you can customize the design and the spectrum and more specifically match the grow light to your grow space. A lot of LED light manufacturers pack a ton of diodes or chips into a tiny box and use it like the old HPS reflectors - basically a concentrated burst of light from 1 center point. This is missing out on the opportunities to be more efficient with LED. Spreading out the sources of light across your entire tent is the only way to get an even coverage. Most commercial designs are trying to achieve even coverage by packing even more watts into a more concentrated box and forcing you to hang the light higher or use special lenses, but that's just not efficient.

You want to learn how much light your plant needs to grow, which increases as they progress from seedling/clone to vegetative and flowering. Cannabis can handle up to 1500 PPFD of light while flowering in enriched CO2 environments. If you're not using CO2 though, cannabis can only make use of about 600 PPFD. Pretty much every grow light on the market will grow plants, whether they're purple or white or orange or blue. The spectrum does matter, and the latest consensus is that plants are most healthy in a full spectrum of light, with peaks in the red and blue wavelengths. But again, I would not even pay attention to this when buying a light because what is probably most important is that you're giving your plants as much light as they can possibly use. You need to know the PPFD, either through charts or your own meter, to dial in the exact amount and make the wisest purchase.

For your specific cabinet of 2x3 feet, I would shoot for one rectangle or two square LED lights that most snugly pack your 2x3 footprint. You want a few inches around the LED for heat ventilation, so maybe two 18" x 12" fixtures, or one 18" x 30" fixture. If you can do that then you're pretty much guaranteed to get over 600 PPFD across the entire cabinet no matter the brand or tech. And it's as simple as that. More photons hitting your plants = faster growth and more yield.

When plants photosynthesize to grow, they take in h2o from roots and co2 from the air, then use photons as a catalyst to transform that water and co2 into carbohydrates and oxygen. Your plant will grow itself as fast as it naturally can, until it's limited by lack of water, co2 or light. Photosynthesis doesn't care about hydro or soil, Foxfarm nutes or Advanced Nutes, this brand LED or that brand LED. It's just a math equation so the only things that really matter or the most important things to consider are the factors going into that equation.

Manufacturers do not inform you about this and rarely publish accurate PPFD charts, so unfortunately you just have to take a guess or start measuring the factors yourself. But like I said, as long as you try to cover your footprint as evenly as possible, the differences between brands and techs and everything else is negligible because you'll be capped by CO2 anyway. I wouldn't call any indoor grows without CO2 great these days, but you'll still get good results.

Getting great results would require a sealed environment, supplemented CO2, controlled temperature and humidity, and a lot more light. Would need to be monitoring all those variables of the photosynthesis equation and keep them dialed in perfectly. Maintaining 1200+ PPFD across a wide footprint is impossible for most commercially designed brands of LED lights because of that severe drop-off just inches outside of the direct footprint of the concentrated box. It's even more important to have even coverage when using CO2, so getting in the habit now might save you a lot of money if you plan to upgrade.

I wouldn't recommend any brands these days. I think it's better to educate yourself and build your own light. The knowledge to do so would at least help you make an informed purchase and know what's worth the price. You'll save money, yield more, waste less energy, be a better consumer, and encourage these manufacturers to get on board.

 

[LB07]

What scientific said. Here's what 600w of CREE CXB3590 get you in a 4x4. Home built for under $900. Canopy ppfd in the 8-950 range. Essentially the maximum amount of light for a space minus c02. After 800 you get diminishing returns on yield without c02.

 

[Scientific]

The only measurement you should be concerned with is PPFD...

That was a hell of a write up! I think I'll paste that in my collection. We've come a long way since foot candles was the standard...

 

[ConstantGreen]

Aww, thank you! I browsed your collection and really liked the excerpts and that you reference to posts that you enjoyed. Thanks for sharing! The first link in the collection didn't work though. "Suggestions on buying the best LED light"

There's so much to say on the topic of lighting. It really does get complicated and advanced when you want to push for a truly optimal setup. If I say anymore on the topic now I'll just go into a mindless rant.

And thank you for taking the moment to edit down long quotes!

 

[Scientific]

The first link in the collection didn't work though. "Suggestions on buying the best LED light"

Thanks. I fixed that. Here it is: Icemud's "Suggestions on buying the best LED light"

 

[ConstantGreen]

Thanks. I fixed that. Here it is: Icemud's "Suggestions on buying the best LED light"

That's a good one!

 

[Techman]

Take a look at out Professional Line of COB LED Grow lights at SunPlusLED | Florida | SunPlus USA

let me know if you have any questiion

Happy Growing

T.