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Thread: Guide: How to Find the Right LED Grow Light For Any Grow Space

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    Default Guide: How to Find the Right LED Grow Light For Any Grow Space

    Hey guys,


    I’ve seen plenty of threads and posts in this forum discussing which LED lamp is the best or best suited for a certain grow space/grow area. I see people recommend lamps left and right without any information or arguments as to why that particular lamp would be good for the grower in question. We have to remember, a grow light that works well in a 2x2’ (4 sq ft) area would not at all be enough in a 4x4’ (16 sq ft) area. I’ll try to keep this post brief but if you’re interested in this topic we have a more in depth post on our website:
    How to Find the Right LED Grow Light

    We have also written about the “watt/sq ft”-principle which can be used to determine how powerful grow light one needs, although this way is much, much, less accurate than the method we’ll discuss below.
    To read about watt/sq ft, we have both an article about it HERE
    How Many Watts Per Sq Ft for Cannabis

    The same article is also published by Maximum Yield:
    https://www.maximumyield.com/find-th...nciple/2/18045



    Finding the right LED grow light
    First of all you need to know the size of the area you intend to use. Are you growing in a 1x1’ closet? In a 2x2’ tent? In a 5x5’ grow room?
    If you haven’t yet decided which space is right for you but you know how many plants you intend to grow, you should estimate around 2-3 sq ft (0.2-0.3 sqm) per plant. Plants grown in small pots or autoflower plants tend to grow small-ish while plants grown in large pots and photo-plants tend to grow bigger in size. If a plant is vegged for a long time and trained well, it can obviously grow bigger than 3 sq ft, so take these recommendations with a pinch of salt.
    This means that you can snuggly fit four medium sized plants in a 3x3’, 9 sq ft (90x90 cm, 0.81 sqm) tent.

    Once you’ve determined the size of your grow area, you can then look at which lamps are suitable for it.


    PPFD (light intensity)
    PPFD, Photosynthetic Photon Flux Density, simply put means light intensity and it’s measured in µmol/m2/s. In a dark room, the PPFD would be 0 µmol/m2/s and in direct sunlight around 1500 µmol/m2/s.
    Low-light plants, like microgreens, salads, leafy greens, etc, do well in low-light intensity of around PPFD 300 µmol/m2/s.
    Mature high-light plants, like cannabis, do well with around 600-900 µmol/m2/s during flowering. During their early stages, they are more fragile and are less capable of handling high light intensity and high concentration of nutrients compared to their flowering stage.

    Typically, these PPFD levels are recommend throughout a cannabis plant’s life cycle:

    PPFD
    Clones/cuttings: 50-100 µmol/m2/s
    Seedlings: 100-200 µmol/m2/s
    Early veg: 200-300 µmol/m2/s
    Late veg: 300-400 µmol/m2/s
    Early flowering: 400-600 µmol/m2/s
    Late flowering: 600-900 µmol/m2/s (sometimes even a bit higher)


    PPFD-maps
    Knowing what light intensity (PPFD) our plants want makes it easy for us, growers, to find a lamp that adequately provides the desired intensity. Brands will show so-called PPFD-maps alongside their lights. A PPFD map is a 2D image showing a certain area, eg 2x2’, and a number of values on this area. The values are PPFD measurements.
    Let’s take a look at two of our lamps to illustrate this point: LEDTonic Q2 (36W) in a 2x2’ area and LEDTonic Q7 (320W) in a 3x3’ and 4x4’ area with walls (tent) and a 5x5’ area with no walls.

    Q2 2x2’ (4 sq ft) with walls


    Q7 3x3’ (9 sq ft) with walls


    Q7 4x4’ (16 sq ft) with walls



    Q7 5x5’ (25 sq ft) with no walls




    On the four maps above you see each lamp and the area it was measured in as well as the grid system that corresponds with the actual PPFD maps at various heights.
    The spread of light and light intensity varies based on the distance between lamp and sensor (or canopy). The higher the lamp is from the measuring point, the lower the intensity will be but the spread of light will be greater.
    We also see that concentrating the same light output from a lamp in a relatively small space (3x3’) compared to a larger space (4x4’) will give vastly different PPFD levels.

    Knowing that mature cannabis plants do well when given PPFD 600-900 µmol/m2/s, we can look at the maps and determine how large an area each setup covers. Naturally, plants will grow even when subjected to lower PPFD levels but their growth potential will be lower. In practice, anything above PPFD 200 µmol/m2/s will stimulate growth but the higher the better. The entire plant doesn’t need to be covered with 600+ µmol/m2/s either so try to determine roughly the average PPFD over the area you intend to grow. A plant receiving PPFD 900 µmol/m2/s on one side and 300 µmol/m2/s on the other side (further away from the lamp) would get roughly 600 µmol/m2/s in average, which is an excellent PPFD average.


    How to read PPFD maps
    Beginning with the Q2 in a 2x2’ tent, we see right away that at 6” the lamp emits decent light intensity in the center, approximately 1.5x1.5’, but pretty low values in the outer edges. We see values above 600 µmol/m2/s in the center and mid-300s besides the center. Around the outer edges the values are around PPFD 100 µmol/m2/s, which would be low for mature cannabis plants.
    This means that the Q2 fills a 2x2' poorly with high enough light intensity for mature cannabis plants. However, the inner 1.5x1.5' has high enough average PPFD to grow cannabis plants well.
    Moving the same lamp up to 12” we see that the intensity decreases in the middle but increases in the outer edges as light is more evenly distributed the higher the lamp is.
    We see PPFD levels in the high 200s in the center and around 200 further out in the entire 2x2' area. These levels would be good values for seedlings and early veg, for instance, but not enough for flowering.

    The Q7, which is almost 9 times as powerful as the Q2 (36 watts vs 320 watts), fills even 4x4’ tents with good light intensity. Looking at the same lamp in a 3x3’ space, we see that the entire area is covered with very high intensity.
    Looking at the Q7 in a 5x5’ open space, we see that at between 12-18” it does a pretty good job covering approx. 3x3’ of the 5x5’ space. When comparing the 4x4’ with walls map with the 5x5’ no walls map it’s also clearly illustrated how big difference reflective walls do for a grow space.


    Conclusion
    The main point I hope you will all take away from this is how to read PPFD maps and apply maps and PPFD values presented by brands to your grow space. If you’re trying to decide between two lamps, look at the lamps’ performance by comparing the PPFD maps. Do the lamps adequately cover the area you intend to grow in with the right light intensity?

    P.S. Some brands (primarily Chinese) inflate their numbers and create fake PPFD maps. Be critical and if possible, try to verify the PPFD maps presented. This can, however, be difficult. We try to be as transparent as we can by video recording our measurements and publishing it to the public. If you’re interested in how PPFD maps are measured and recorded, have a look here:


  2. The Following 7 Users Say Thank You to LEDTonic - Daniel For This Useful Post:

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