Marijuana Light Spectrum

Discussion in 'General Marijuana Growing' started by pauliojr, Mar 30, 2007.


    pauliojr Well-Known Member

    It has been brought to my attention that more then a few people have been getting confused on light spectrums and which ones are better for which stage. Below is a picture that I have edited from Marijuana Seeds Search Garden that divides the kelvin light spectrum in half and tells you which one you would like to use more in what stage. It is posted in another topic and it was brought up to do this. I hope this helps some people out down the road. Thank you all (especially MR. ISSUES).


    beensmoking Well-Known Member

    Yea Rock On That'll Help People Out A Lot!!!

    DoobsDay Well-Known Member

    except for one thing, incandescent and halogens cant be used

    pauliojr Well-Known Member

    Well they can be used, but they are just not ideal for growing.

    DoobsDay Well-Known Member

    induced strecthing, nah ill pass

    pauliojr Well-Known Member

    Haha I hear ya man. I would never even consider using either one. Nice post bro!

    Doctor Well-Known Member

    thanks pauliojr :):):):)

    daydrops Well-Known Member

    It seems like I keep hearing contradictions. I read in a grow book that 5,000 is closest to the sunlight so it can be used thruout the grow; but that plants use more red in the flowering. I have heard from the grow shop that 6,400k is the prefered spectrum because it's the brightest and the 2,700k red is less bright, so the idea of more red durring flowering is BS.

    This chart is different from one I found online which puts pure white sunlight at 5,000k.

    What's the deal? I'll check the archives...

    Ok, here's the spectrum I found online. It looks closer to the understanding of the grow specturm because 5500k is the 'white' light. Can anyone verify this?

    Attached Files:


    babygro Well-Known Member

    hiya daydrops

    Forget 'brightness' it's not relevant.

    The suns 'real' kelvin temperature is somewhere around 5,800 degrees kelvin, but because the sun is not a perfect 'black body' (the standard for calculating kelvin temperatures of light) its adjusted kelvin temperature is somewhere around 6,400 degrees kelvin.

    6,400 degrees kelvin is predominantly 'bluish-white' light and this is the best kind of light and kelvin temperature for vegetative growth - primarily because in nature the time of year Cannabis is in vegetative growth is during the long hot days of summer where the suns daylength is the longest and receives the most 6,400k light. The reasons it changes for flowering is again because of the predominance of the kind of light found from the sun when Cannabis enters it's floral stage - usually at the start of Autumn or Fall when the days get shorter and the nights longer thus reducing down the daylength significantly. Sunrise and Sunset account for almost 50% of the suns light during the short days of Autumn/Fall and sunrise and sunset are made up of almost entirely red spectrum light due to the angle of the suns rays hitting the earths surface. Therefore as sunrise and sunset account for almost 50% of the sun total light output at that time of year it necessarily follows that 50% of that light will be entirely in the red end of the visible spectrum - hence the 2,700k colour temperature being favoured for flowering. In reality a mixture of red and blue light is required in flowering due to the other 50% of the spectrum being more blue in colour.
    toolage, jigfresh, grlsk8co and 2 others like this.

    daydrops Well-Known Member

    great tutorial, babygro. thank you.:peace:

    Vermilion Well-Known Member

    i have a grow light that came with a professional looking incandescent light. its shaped like a cylander looking triangle or something. would that be good for flowering? that way i know for a fact that its a 2700k since it says standard incandescents are 2700k.

    Vermilion Well-Known Member

    i WAS growing vegitatively with a small cfl which i think was a daylight because it stopped stretching lol.

    northerntights Well-Known Member

    incandescent lights are usually not worth the trouble, heat and low light output, just buy a cfl.

    Vermilion Well-Known Member

    but this incandescent is 65 watts, my cfl's are 27 watt and 17 watt. So I don't really have a choice but to go with my incandescent.,

    MightyBuddha Well-Known Member

    Those CFLs will be out more usable light because those are real watts. A 27W CFL is equivalent to 65W incandescent.

    Vermilion Well-Known Member


    I got a small cfl thats 14 watts, and a big one thats 20 watts. the big one takes a couple of seconds to turn on while the small one turns on immediately. Which one should I use for flowering? the big or the small>

    battosai Well-Known Member

    im using three 15w a 27w and two 23w cfls just to veg 3 plants. there is no one or the other. use them both and get more.

    FilthyFletch Mr I Can Do That For Half

    Well this confuses me since Kelvin is a measure of heat and not light such as Lumnes and lumnes are what matters for light or is Kelvin used in regards to color spectrum measurments some how?

    Vermilion Well-Known Member

    i only have one outlet for one light lol. so which should i use? the 20 watt big one which would probably be best for vegging because it dosent say how many kelvins it is. or the small 14 watt one? which btw i dunno how many kelvins it is.

    eastlosg1 Well-Known Member

    try going the cheapest way . I bought 2 input sockets and 2 y's and made a ghetto reflector , so there is 4 cfls in it. And it's putting out 6,440 lumens from some crl torque ( power ) In total it would be like 20 smackers

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