Lighting Questions

I’ve been using a 400watt air cooled MH & HPS. Been doing ok with it, but been thinking about going to a 1000watt HPS for flower. Would my yields be a lot better with the 1000w over the 400w. Or would I be better off with an LED for flower? My growing area is 3’6" x 3’6" x 8’0" height.


I’m sold with LED lights full spectrum … :innocent: They produce much less heat and very budget friendly in consuming electricity… And I have achieved big yielding with them…:wink::innocent::ok_hand:

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I think you’re fine where you are in that size tent

you could go to a 600w, but I kind of think a thousand watt would be Overkill ?

I have a thousand in my 5x5 but I usually keep it on 600w, and I don’t really see a difference (though I imagine there must be some?)

When the canopy gets very thick I’ll turn it to 1000w but in a size as small as yours I don’t think I’d go past 600w, jmo

-best of luck!



This should give you a better idea.


PAR is short for photosynthetic active radiation, in other words mostly only red and blue light, however some orange and yellows, and even some green can actually be photosynthetically active.

Actually, although you won’t find it as common a measurement on HID lights like HPS and MH, it is a more accurate measurement on even those lights as to what they are actually providing for the plants, as far as the spectra that the plants can actually use for photosynthesis.

LEDs can absolutely be used by themselves to get as good of results as HID lights. But unfortunately not even the best LED companies are the best about being completely honest at what it might take to get similar yields under their lights. If you want the same performance, you really need similar wattage and the right lensing to also match deep penetration through the canopy. I personally only use LEDs.


Here is a break down of the electrical magnetic spectra near the photosynthetically active radiation, or PAR, range:

720 - 1000 nm There is little absorption by chlorophyll here. Flowering and germination is influenced. At the high end of the band is infrared, which is heat.

610 - 720 nm This is the red band. Large amount of absorption by chlorophyll occurs, and most significant influence on photosynthesis. (promotes flowering and budding)

520 - 610 nm This range includes the green, yellow, and orange bands and has less absorption by pigments.

400 - 520 nm This range includes violet, blue, and green bands. Peak absorption by chlorophyll occurs, and a strong influence on photosynthesis. (promotes vegetative growth)

380 - 400 nm Start of visible light spectrum. Process of chlorophyll absorption begins. UV protected plastics ideally block out any light below this range.

315 - 380 nm Range of UVA ultraviolet light which is neither harmful nor beneficial to cannabis plant growth. Although some studies do seem to indicate this band might stimulate resin production, as THC does seem to have UV blocking properties, and these frequencies may be able to stimulate the plant to create these UV protecting resins without actually having toxic or negative effects on the plant’s biological function.

280 - 315 nm Includes harmful UVB ultraviolet light which causes cannabis plants colors to fade.

200 - 280 nm UVC ultraviolet range which is extremely harmful to cannabis plants because it is highly toxic.

And above these wave lengths dwell the very long radio/TV waves (even microwaves), and below it resides the ultra short X-rays and gamma rays.

Posted by Garrigan62


I agree, 600W is the number I’d aim for.



Hope this helps. I know I have given a lot of info. just bored today…lol



Thanks guys and gals!

Hey guys.
I have a room 2.6 , 2.6 height 2.1.
I’m looking at changing my 2 600 don’t lights to led.
I’m not sure on how many I’m going to need.
In 600 or 1000 led.
Can you assist

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I meant 2 600 sont lights

Try for 50 True watts per sq. ft.

What is the unit of measure for your tent size, feet or meters?

If feet you need around 300 true watts (actual power draw of the LED).
If meters you need around 850 true watts.

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@garrigan62 has provided lots of lighting info today. Perhaps he’ll drop a little here too.

It’s 2.6 metres squared by 2.1 high.
Will 2 led at 600 w or
2 led 1000 be ok

I think you’re going to need the higher ones. It’s really about the power draw, not the equivalent number. Example, my 900watt lights are actually 418 watts. You’d want 2 of them or some other equivalent.

What would u suggest.
6 plants in the area.
How many led and what w is the most suitable.
I’ve used 600 sont only in the past.
So I’m not sure. But I definitely want to go led .

maybe 4 of these to get good coverage? Viparspecta is the only LED I have experience with. Other might have better ideas. 200watts x 4 = 800 true watts. You’d be right there.

Askl and you shall


Hope this helps



of Plants Square Feet Recommended LED Wattage

     1               1.                          25

      2.              2.                         50

      4.              4.                         100

      6.               6.                        150

      8.               8                         200

      10.            10                        250


of Plants Square Feet LED Wattage

         1.               2.                                    50

         2                4.                                   100

         4.               8.                                   200

6. 12. 300

         8.              16.                                  400

         10.             20.                                 500


of Plants Square Feet Recommended LED Wattage

          1.                4.                       100

          2.                8.                       200

          4.               16.                      400

          6.               24                       600

          8                32.                      800 

          10              40.                     1000

Quick Chart: Recommended LED wattage for high light plants (25 actual watts/sq ft)

1’ x 1’: 25 watts

2’ x 2’: 100 watts

3’ x 3’: 225 watts

4’ x 4’: 400 watts

5’ x 5’: 625 watts

6’ x 6’: 900 watts


There you go. Listen to him over me all day long…

Thanks for this post that helps me understand the why of certain lights being not so good for the plants .

Your very welcome any time

B Safe

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Anyone use cmh 315w? Just copped one and it’s the truth! My tent is 4x2x6.

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