LED light size question

Hi guys, new here, my second thread.

Have two young plants, day 6, growing away in a tin foiled lined large storage box, under a CFL 150w/6500k/1600l, and all going fine. :crossed_fingers:

Eventually when I transplant them they will be moving onto a 3’x3’x6’ tent, under an led grow light.

What would be an adequate wattage size led panel? I’ve been thinking 600w, but just read on one thread that 600w is about right for a 4’x4’x6’. Would 600w be OK for the smaller tent?

All help appreciated.

You need 50watts per square foot. So you have 9 sqft which calculates to 450 watts. This it true wattage not what the light claims to be. Actual wattage should be available in the light specifications. Hope this Helps my UK friend

Cheers I was thinking the 600w cheaper eBay jobs are probably closer to 450w so I may with one. If its totally rubbish I can fall back to my CFLs, I think once in the tent and loft I may need an extra bit of heat so the cfls may not be a bad idea.

I may just got 3x 175w cfl (I have 2 spare atm) 6500k 2000l, they draw 35w, and so just over 100w for the 3.

I’d have to do some maths, and see what the wall draw is to the LED panel is, but the cfl may be a cheaper option. Bulbs cost about £15 for the 3, the panel about £60. I wonder how long the break even point is? I bet it’s a long time.

Decisions decisions.

I bought the cheap ebay lights. If you go that route you will need to buy 2each of the 1200watt lights. They only draw 220 true watts. But you can get two lights for about $170USD. I also bought the 600w one and that wouldnt work for you. Actual watts on that one is only 100 true watts. I think you would be happy with the 2-1200watt lights. You have some time to think about it.

That’s great info. The old saying is alway true it seems. Buy cheap buy twice!

Have you reperpoused the 600w for seedlings then?

Is there any negatives, baring energy usage, to cfls 6500k over an led panel. As I may for the first lot just use bulbs. If all goes well and I get more experience (read confidence) I may invest in an LED panel.

I have some more basic questions, but il keep them in the “basic” thread I started.

Also I woke this morning to two more new leaves on both plants :grinning:

Great news on the plants. I am actually using the 1200s on the seedlings about 18 inches away. They seem to love it. If you are going to invest more money I would go with the LEDs. More bang for your buck or pound for you lol. I have to go get an SD card for my camera then I will start my grow journal today so you can see my setup. You can also read my thread DIY True High Pressure Aeroponic System for $300 - #10 by MAXHeadRoom This is my setup.

The led’s should be more efficient but I would guess that the 600 watt panel will actually draw only around 220 watts. 1,000 watt would be closer.

Spec sheet for 600w no name brand light. Actual true wattage is only 100 watts


  1. Maximum LED Power: 600W
  2. LED Quantity: 60Pcs Exclusive 10W Double Chips LED
  3. Actual Power: about 100W±5% Power, Much Better Than the Same Product in Market
  4. Spectrum: 380-410, 450-470, 620-630, 650-670, White: 730-740
  5. Amperage: 5.45A@110V, 2.73A@220V
  6. Lumen: 58628 lumens
  7. Coverage Area: 2.52ft forVeg, 21.5ft for Flower
  8. Decibel of the Light: About 56DB
  9. View Angle of LED: 90/120 Degree Mixed
  10. Lifespan: 50000-100000 hours
  11. Material: Iron & Acrylic
  12. Housing Color: White
  13. Dimension:(12.2 x 8.27 x 2.36)" / (31 x 21 x 6)cm (L x W x H)
  14. Weight: 68.78oz / 1950g
  15. Light Color: All Colors

Package Includes:
1 x 600W LED Grow Light
1 x Free Power Cable
1 x User Manual

Actual power for 1000 watt light is 130w-180w
Actual power for 1200 watt light is 180w-220w

spec sheet for 1200watt light says 300watt power draw

Who knows who’s telling the truth.

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I’m confused by the way they are rated.
I the say 600w but say actual power is 100w. I always took this as the 600w is the equivalent of a 100w incandescent.

Much the same was a CFL running atm for my sproutlings, are rated 150w, but actually draw 30w from the wall.

I know the cheap Chinese LED panels always fall sharp of advertised, that’s why I thought a 600w rated, (that pulls 100w) would probably give off around 400w (of plant power) in reality.

I’m I totally off the mark in my thinking. If I’m not your 1200w panels are probably pushing out 900+ watts of plant power

Yes I’ve just created a new power output term. Lol. Plant Power output is what the bulb actually gives off, not what it’s stated to give off, and not what it draws at the wall.

There is probably a real term, but I don’t know it.

@MAXHeadRoom that type of panel is exactly what I was looking at. Around £50-60 here. Problem 80usd ish.

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Yes there is. Its called PAR. Photosynthetically active radiation I dont want to confuse you to much but this is a better comparison than wattage. But they lie about that value too.


@TheDuke if you’re worried about true wattage just go HID. Growing only 2 plants you’d only need a 250w MH/HPS. They’re cheaper - and in my opinion, give you a better grow.(I’ve grown with both HID and LED)

Bloom - 12/12 @ 10 cents per kwh will run you around $15 a month. I only ever grow 2 plants and average a yield of 6 oz.

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What’s happening is they are quoting the maximum power output of the led’s used (say,60 X 10 watt equals 600 watts) but they build them for maximum life and efficiency. Somewhere around 35% of output. You crank the driver up and the led’s get inefficient. At the power level they are driven they are outputting about 65% of the electricity as photons. Higher than anything else. As for “cheap Chinese manufacture”, the parts are all probably sourced from the same two or three places everyone buys em from.

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Thanks guys. I had a think over night and have decided the first yield I’m going to use CFL, I’ll probaly go Hid after that.

The main reason for CFL is pennies. Being a first time set up the wife is already noticing the costs adding up, and she isn’t fully on board, so the sell is getting harder.

Also at about 6 weeks in, I’m going to start another 2 plant grow, hopefully that will generate enough oil for what we want. Yield size is important obviously , but in my case the majority of the plant can be used, not just the bud, so total maximisation from the off isn’t of the highest concern. More of a learning process, that I can slowly improve on.

Struggling with humidity the last few days. Hopefully as we have had rain, and still raining, that should be up today. Not checked yet, still in bed. (6am).

@majicmarkers What distances do you hang your HIDs from the plants?

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@FrostyJake I was initially looking at LED panels, but the cheaper ones don’t seem to be that great. Them spectral kings, seem the nuts, but out of my price range.

The economics don’t make sense for a two grow set up. If I was going into business maybe. But my project is just to generate a few Oz of oil every other month. Also i suppose it would be rude not to smoke some. But tbh I’ve not smoked in 20 years. And I imagine this Afghan I have is going to be a little stronger than 1990s resin was.

If the prices was like the 90s I wouldn’t need to grow. £200 +/-£20 strain dependent, or $20usd Oz around my way. :confounded:

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When looking at LED’s, you want to look at the actual wattage consumed or used by the LED system, as @MAXHeadRoom pointed out.

For example, you will often see a LED that is said to be a 300 watt LED system, and it will have 100 x 3 watt LEDs, but if you look at how much it actually uses, it only uses around half that, say only about 150 watts. For the sake of simplicity, I’ll call the first the “Label Watts” and the second the “Actual Watts”.

The difference comes from the fact that the individual LED’s “Label Watts” are what the LED diode can be maxed out at before it will burn out, but it is not the best for longevity of the LED diode, nor for the best efficiency of turning the electrical watts into actual light, or Photosynthetically Active Radiation (The actual light that can be used for photosynthesis, abbreviated as PAR), instead of a lot of the electricity ending up being wasted as heat when running the diodes at nearer the max wattage.

Also, depending on the brand, some manufactures name their LED system by its actual watts and not the label watts of – the individual diodes, in total – that make up the system.

And to make things a bit more complicated, LED technology is advancing so rapidly, they are becoming more and more efficient and effective all the time, so a 150 actual watt LED system that was made around 3 to 5 years ago will not be as effective at producing the same amount of PAR as a 150 actual watt LED system made just this year.

And so, depending on the brand, the quality, and the way the LEDs are focused through different types of lenses, one type of 150 actual watt LED system might cover a very different area than another type of 150 actual watt LED system.

So the only way to be absolutely sure is to check with the manufacturer, and what they claim that their system will cover.

However, there are some basic “rule of thumb” guidelines you can kind of use to judge and compare various brands to each other and for getting an idea of what area they might cover.

It is fairly well known that with traditional HPS light, 50 watts per square foot is considered the standard, as @MAXHeadRoom also pointed out. And there is a similar formula used for LED and it is anywhere from about 25 actual watts to about 35 actual watts per square foot. 35 watts per square foot being the more common accepted standard from some of the more reputable LED manufacturers.

And so:

3’ x 3’ = 9 square feet

9 square feet x 25 watts = 225 watts

9 square feet x 35 watts = 315 watts

And so you probably want a LED system that actually uses or consumes – 225 watts minimum, and up to about 315 watts maximum.

Happy growing,



@MacGyverStoner thank you, much appreciated.

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You are very welcome.


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Truly, a good led will be an investment you won’t regret and it will beat those cfl’s like a redheaded stepchild lol. Also, you can add panels as you need them. That way you can spread the cost out. I didn’t get enough light until my second grow.

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I’m going to get a 3’x3’x6’ at the weekend. For the two 7 day old saplings to go into when ready to transplant.

Lights I was reckoning on about £60 for the 600w panels off ebay, but now I know they are no good, so I’m going to stick with the CFLs, 4x 175w 2000l 6500k, I calculated today they will cost, 44pence per day to run (at the mo ment they are under a single bulb so 11pence per day), on my current electric plan of 16pence per Kwh. (don’t know if that is cheaper or more expensive than USA)

I’m going to set a second tent up, and alternate the grows, probably have the 4 plants share the same tent untill they out grow the space (if I’m lucky).

I’m really grateful for all the help and advice, but for the first grow, I’m going to stick to CFLs, mainly due to mounting costs, then migrate to something better in the future.


You will be able to use the cfl’s later for side lights. They won’t go to waste.

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