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Determining the Ideal LED Grow Light Setup

Determining the ideal LED grow light setup for your grow depends on a lot of variables:

  • Plant / crop:
    • Light demands
    • Photoperiod (day / night hours)
  • Growing area:
    • Size
    • Shape
  • Your goals:
    • Vegetative, flowering or both?
    • Economize vs. maximizing yield
    • Active growth vs. maintenance

By selecting the appropriate footprint coverage using our lights, you can achieve the ideal grow!

Plant Lighting Intensity and Duration

Different species of plants (and sometimes even different varieties or cultivars within species) require different amounts of light for ideal growth, and flowering plants often require more light while flowering and fruiting than during vegetative growth.

The total amount of light received by a plant each day is determined by both the intensity of the light and the duration of the illumination. For example, if you have a light running for 2 hours per day, it only takes 1 hour for a light that is twice as intense to create the same total amount of light.

To measure the total amount of light per day, the Daily Light Integral (DLI) counts the total number of photons per day in the PAR (Photosynthetic Active Radiation) range of 400-700nm. DLI is measured in units of mol·m-2·d-1 [moles of light (mol) per square meter (m-2) per day (d-1), where 1 mole of light is roughly 6×1023 photons].

For every plant there is a DLI range which will maximize growth and production; less than this range will result in poorer growth / yield or even no growth, and more DLI will be wasteful (costing more than the additional yield justifies), or even harmful to the plant. Determining this ideal DLI range is tricky as it not only depends on the plant type and growth stage, but can also vary with other factors in your growing environment such as temperature, humidity, fertilization / nutrient availability, CO2 supplementation, the exact lighting spectrum (including outside of the PAR range measured by DLI), and more. This deserves an entirely separate in-depth discussion, coming soon.

Complicating matters more, plants can be divided into 3 categories:

  1. Short-day plants flower when the night length is greater than their critical period; until then, they stay in a vegetative growth mode. Cannabis sativa, Cannabis indica, cotton and rice are examples of short-day plants.
  2. Long-day plants flower when the night length falls below their critical period. Peas, lettuce and carnations are examples of long-day plants.
  3. Day-neutral plants do not initiate flowering based on the night length, but instead on some other stimulus such as reaching a particular size or age, or period of cold or drought. Cannabis ruderalis ("auto-flowering" cannabis), peppers, tomatoes and cucumbers are examples of day-neutral plants.

Sometimes very similar plants fall into 2 or 3 of these categories, as is the case with Cannabis, strawberries and mulberries.

Note that some plants still require a dark period each day, even if they are day-neutral, short-day (vegetative stage), or long-day (flowering stage). For example, tomatoes grown under 24/7 light will get chlorotic leaves and grow poorly. Giving plants a 4-6 hour resting period each night is generally beneficial both to your crop and your wallet.

To the extent allowed by plants' night-length constraints, you can increase the DLI by keeping the light on longer each day, without having to increase light intensity. For short-day plants like Cannabis indica and C. sativa, it is particularly necessary to have high light intensity during the flowering stage, as the DLI cannot be increased by extending the daylight hours.

LED Grow Light Intensity and Coverage

Each model of our PhytoMAX lights uses 5W LEDs to create light. The average light output (intensity) per LED is the same; the larger models simply have more of them to create more light. All Black Dog LED lights are designed to spread the light as evenly as possible over the entire lighting footprint; the intensity of the light within the footprint and the size of the footprint are controlled by how high you hang the light above the plants.

Moving the light closer to the plants will decrease the size of the footprint but increase the intensity because you're spreading the same amount of light over a smaller area. Moving the light further from the plants increases the size of the footprint but decreases the intensity.

No matter what size light you're using, you can get an equivalent percentage increase in DLI by either shrinking the footprint area or increasing lights-on hours. For example, you can get a 25% increase in DLI by shrinking the covered footprint by 25% (e.g. from 16 square feet to 12 square feet2 square meters to 1.5 square meters), or by increasing the hours the light is on by 25% (e.g. from 12 hours to 15 hours).

Growing Area Shape

Our PhytoMAX lights have a square footprint area, but that doesn't mean you can't use them in rectangular growing areas. There are three options for covering non-square areas:

  1. Use a light big enough to cover the longest dimension:
    • For slightly-rectangular LED grow light coverage this can be the least-expensive option. Using reflective materials on especially the longer sides of your growing area will help to make use of all of the light in this setup. If your growing area's longest side is more than 1.5 times the length of the shorter side, you probably want to use option number 2 or 3 for better, more-economical results.
    Slightly Rectangular Footprint Coverage with a Large Light
    PhytoMAX 800
    5 feet150 cm
    4 feet120 cm

    Imperial     Metric

  2. Use multiple lights:
    • By hanging two or more lights side-by-side you can create a rectangular footprint. For example, two PhytoMAX 200's hung 2.5 feet76 cm apart (on center) will cover a 2.5 x 5 foot76 x 152 cm rectangular area, using our maximum recommended flowering footprint for photoperiod-sensitive Cannabis. In a partial combination with option #1 above, these same two lights could also cover a 2.5 x 4 foot76 x 120 cm area, a 2 x 5 foot60 x 150 cm area, or even a 2 x 4 foot60 x 120 cm area.
    Rectangular Footprint Coverage with Multiple Lights
    PhytoMAX 200
    PhytoMAX 200
    5 feet150 cm
    2.5 feet75 cm

    Imperial     Metric

  3. Use a light mover to "stretch" the footprint shape:
    • Hanging the light from a light mover will change the shape of the light's effective footprint. The actual footprint is still square, but by moving this square footprint back and forth in a line, it is effectively transformed into a rectangle. Often the cost of an appropriate larger light with a light mover is less than the cost of two smaller lights without a light mover, making it the most economical choice for many rectangular growing areas. Light movers have a lot of benefits and considerations, detailed below:
    Using a Light Mover to Cover a Rectangular Footprint
    PhytoMAX 800
    6.25 feet190 cm
    4 feet120 cm

    Imperial     Metric

LED Grow Lights on Light Movers

Light movers are beneficial for two reasons:

  1. Changing the effective shape of a light's footprint:
    • By moving a light back and forth in a line, light movers "stretch" the effective footprint of a light into a different shape, as long as you keep the effectively-covered footprint area the same. For example, a PhytoMAX 800 can normally cover a 5 x 5 foot area (25 square feet)150 x 150 cm area (2.25 square meters) when it isn't on a light mover, but moving it back and forth can make it cover a 4 x 6.25 foot120 x 190 cm area or a 3 x 8.3 foot90 x 245 cm area (both 25 square feetroughly 2.25 square meters), although each setup requires a different light hanging height above the plants. When on a light mover, the light should ideally be hung at the appropriate height to get a square footprint as wide as the shortest side of the effective rectangular footprint area. For example, to cover a 4 x 6.25 foot120 x 190 cm area, the PhytoMAX 800 hung from the light mover should be hung at the appropriate height for a 4 x 4 foot120 x 120 cm footprint (24 inches61 cm above the average height of the canopy). This square footprint is moved by the light mover to create the rectangular effective footprint.

    Imperial     Metric

    Using a Light Mover to Cover a Rectangular Footprint
    PhytoMAX 800
    6.25 feet190 cm
    4 feet120 cm
    Side View
    PhytoMAX 800
    Height:
    24 inches61 cm
  2. Increasing light distribution to raise yield
    • When a light is hung overhead in a static (un-moving) manner, plants will naturally orient their leaves to catch as much light as possible. This often results in upper leaves shading out the lower leaves and flowers of the same plant. To some extent this issue can be overcome by increasing the intensity of the light, but by simply moving the light back and forth and mimicking the sun's natural daily traversal of the sky, light can be more evenly and efficiently delivered to all leaves on the plant. We've seen 10-20% increases in yield when a light is on a light mover covering the same size area, even when the light isn't being moved very far.

      To some extent, hanging multiple un-moving lights provide many of the same benefits; having the light come from many angles helps to nourish more of the lower leaves. However, placing multiple-light setups on light movers will still increase light distribution and yield.

Considering how inexpensive light movers are to purchase initially, and how little electricity they take to run (typically less than 5W!), light movers are often the most economical way to squeeze extra yield out of a grow light.

Large Areas

When setting up larger growing areas, it is important to consider plant access. You'll need to be able to reach the plants to take care of them and even just to harvest them; we generally recommend setups with no more than a 4 foot120 cm reach to access any plant. This generally requires aisles in larger grows, unless the plants are on movable carts to allow on-demand creation of aisleways.

In general, the ideal setup for larger growing areas minimizes aisle space while still allowing easy access to all plants. This requires adjustment for the exact size and shape of the area, as well as the placement of doorways. The staff at Black Dog LED have decades of experience setting up larger growing operations and we're always happy to help with lighting setup design; simply contact us or call us at 720-420-1209!

Your Goals

The ideal LED grow light setup for your situation depends on what you want out of your grow, for example:

  1. Growth phase use: vegetative, flowering or both? If you want to use the growing area for only vegetative or flowering, you only need to consider the lighting intensity for that growth phase. When using the area for both phases of growth, it is best to design for the most light-demanding phase (usually flowering).
  2. Economize vs. maximizing yield: once the plants' minimum lighting requirements (DLI) have been met, increasing the DLI will increase yield. Up to a point, increasing the DLI by a certain percentage will increase yield by a "linear" equivalent percentage; for example increasing the DLI by 10% may increase yield by 8%, and increasing DLI by 20% would increase yield by 16%. When you start giving the plants as much DLI as they can handle, this yield return on increased intensity starts to fall off and is no longer linear; for example if you've got a very high DLI to begin with, increasing it by 10% may only give a 4% increase in yield. Past a certain point increasing the DLI will not increase yield at all, and may even hurt it if the plants are being harmed by too much light.

The Perfect LED Grow Light Setup

A configuration calculator is coming soon! For now, here are some basic recommendations, based on flowering daylength-sensitive Cannabis plants. Four different configurations are given for each of our PhytoMAX light models:

  1. Minimum: At this DLI configuration, we're sure you'll be happy with the results; plants will grow and flower vigorously with dense, high-quality flowers. Yes, you can go below this a bit (increase footprint size and hanging height) and still get decent results, but they won't be up to our standards.
  2. Medium: At this DLI configuration, we're sure you'll be thrilled with the results; quality may go up slightly and yield per square footmeter will go up.
  3. High: At this DLI configuration, you're still going to see an increased yield per square footmeter roughly equivalent to the increased DLI, although by "overdriving" the plants with so much light you may need to pay a lot more attention to your plants to ensure they're happy. Maintaining proper watering, fertilization, pruning and support becomes more critical as the DLI increases, so we would not recommend this level for beginning growers. Increasing DLI beyond this point will probably not result in a linear rise in yield, and the grams per watt yield will probably start to decrease, and costs go up.
  4. Extreme: At this DLI configuration, you're probably maximizing yield per square footmeter, but in terms of yield per watt of electricity used (grams per watt) you'd probably be better off spreading the light out over a larger area or more plants. We would not generally recommend raising DLI above this point as it is most likely going to be wasteful, although every growing situation is different, and unique growing techniques may make use of all this light!

Imperial     Metric

Light Light Amount (DLI) for Flowering Photoperiod-Sensitive Cannabis
Minimum Medium High Extreme
Footprint Hanging Height Footprint Hanging Height Footprint Hanging Height Footprint Hanging Height
PhytoMAX 1000 5.5 x 5.5 feet (30.25 ft168 x 168 cm (2.8 m2) 32 in.81 cm 4.5 x 4.5 feet (20.25 ft137 x 137 cm (1.9 m2) 26 in.66 cm 4 x 4 feet (16 ft122 x 122 cm (1.5 m2) 24 in.61 cm 3.75 x 3.75 feet (14.1 ft114 x 114 cm (1.3 m2) 22 in.56 cm
PhytoMAX 800 5 x 5 feet (25 ft152 x 152 cm (2.3 m2) 29 in.74 cm 4 x 4 feet (16 ft122 x 122 cm (1.5 m2) 24 in.61 cm 3.5 x 3.5 feet (12.25 ft107 x 107 cm (1.1 m2) 20 in.51 cm 3.25 x 3.25 feet (10.6 ft100 x 100 cm (1 m2) 19 in.48 cm
PhytoMAX 600 4.25 x 4.25 feet (18 ft130 x 130 cm (1.7 m2) 25 in.64 cm 3.5 x 3.5 feet (12.25 ft107 x 107 cm (1.1 m2) 20 in.51 cm 3 x 3 feet (9 ft91 x 91 cm (0.8 m2) 17 in.43 cm 2.75 x 2.75 feet (7.56 ft84 x 84 cm (0.7 m2) 16 in.41 cm
PhytoMAX 400 3.5 x 3.5 feet (12.25 ft107 x 107 cm (1.1 m2) 20 in.51 cm 3 x 3 feet (9 ft91 x 91 cm (0.8 m2) 17 in.43 cm 2.5 x 2.5 feet (6.25 ft76 x 76 cm (0.6 m2) 14 in.36 cm 2.25 x 2.25 feet (5.06 ft69 x 69 cm (0.5 m2) 13 in.33 cm
PhytoMAX 200 2.5 x 2.5 feet (6.25 ft76 x 76 cm (0.6 m2) 14 in.36 cm 2 x 2 feet (4 ft61 x 61 cm (0.4 m2) 12 in.30 cm 1.75 x 1.75 feet (3.06 ft53 x 53 cm (0.28 m2) 10 in.26 cm 1.7 x 1.7 feet (2.9 ft52 x 52 cm (0.27 m2) 9.5 in.24 cm

 

We're also happy to help- contact us online or call us at 720-420-1209 with any questions.

17 thoughts on “Determining the Ideal LED Grow Light Setup”

  • Dr Bryant

    I am A FIRST TIME home grower of cannabis in a state that has legal MMJ and I am qualified to grow 6 home cannabis plants. I want to have both a veg room 2ft x 4 ft and a flowering room of 4x6ft both 6 ft in height. What lights would you recommend for the two separate grow rooms so I can have continuous crop harvest?

    Actually your chart above is very helpful. i would get the PhytoMax 1000 for the flowering room with a light mover. Can you give me a quote?

    Dr B

    Reply
    • Kevin

      Hello!

      For the 2'x4' veg room a PhytoMAX 200 on a light mover would work great and be the least expensive option.

      For the 4'x6' flowering room, a PhytoMAX 800 on a light mover would produce great results over the entire area, but the PhytoMAX 1000 would produce higher yields.

      I will send you a quote in email.

      Reply
  • Mark

    I buy and resell fruit plants from Tissue Culture and only need a minimal time of growth. I'm looking to keep the plants healthy and not necessary push them. I have 4X8 grow trays which can accompany 576 plants. I want to run a light mover. My Questions. I know the recommendation for PhytoMax 200 is 3.5 ft. for Vegetative State. With the last 6 inch would the plants still receive light? If I increased the distance by (?) and added more time (?) couldn't I achieve desired results? Also, I was told the LED on a light mover is not possible because of light saturation, intensity etc. Is it possible to put the light mover on a 5ft light mover to extend the light to the desired 8ft. As stated I'm not trying to push the plants just adequate light. Final question. I was offered a simple 400 watt HID for around $200 and light mover for $200 and they said this could cover the area good enough for what I'm trying to accomplish. If the LED can't spread to 8 ft would it be more economical over the next a couple of years to just stick with HID. Thanks, Mark

    Reply
    • Kevin

      Hello Mark,
      The early stages of tissue culture (still in the flask) are much like the early stages of cloning from cuttings, and do not require much light at all. For the very low level of light you need for these stages, the PhytoMAX 200 would be able to cover a full 4x8 foot area if put on a light mover; to make it cover the full 4 foot width, the ideal hanging height would be about 22 inches above the plants. After the plants are out of the flasks though, this low level of light may be too little- but it depends on the type of plant, and as you point out you can increase the duration of lighting each day to make up for this, to the extent possible.
      Cheers!

      Reply
  • ben gale

    im going to do a 11x6 room with two scrog nets at 4x4 i was thinking about getting two phyto 800s is this to much or should i get the 600s? Im guessing the hanging height is from the top of the plants am i right?

    Reply
    • Kevin

      Two PhytoMAX 600's would work very well, but two PhytoMAX 800 lights(one for each 4x4 SCROG net) would increase your yield even more. The hanging heights given are from the tops of the plants, so for a PhytoMAX 800 over a 4x4 area, the hanging height would be 24" above the tops of the plants, as given in the table above.

      Reply
  • mosh

    For a 5x5 tent would you recommend 4 of the 200watts to better spread, or would the 800,or 1000 be better. For cannabis by the way

    Reply
    • Kevin

      Hello,
      More, smaller lights will always give better spread than 1 large light of the same wattage. Since the PhytoMAX 200 light is 215 watts, 4 of them would be 860 watts, while the PhytoMAX 800 would be 800 watts, and the PhytoMAX 1000 would be 1015 watts. So in order of "most power / most light" to least, it would be: 1 PhytoMAX 1000, 4 PhytoMAX 200's, then 1 PhytoMAX 800.

      Reply
  • Petr

    Hello, I'm going to grow cannabis for the first time.
    Thanks for the detailed analysis of everything on your site!
    My blooming area will have a size of 6ft x 6ft (may be 6.5ft x 6.5ft) for the nine plants (3x3) and veg area of 5ft x 5ft.
    Please advise the best solution, I went through a few variations such as PhytoMAX 600 x 4, but is now focused on this - PhytoMAX 400 x 6 (3x2) with light mover and
    PhytoMAX 400 or PhytoMAX 200 x 2 for the veg area, with light mover both.

    Reply
    • Kevin

      Hello,
      For a 6x6 foot or 6.5x6.5 foot flowering room, 6 PhytoMAX 400's would be an extreme amount of light and would probably cause problems for you. 4 of the PhytoMAX 600 lights for that space would be at the limit of what I would recommend for maximum light; I believe anything more than that would be wasteful and possible harmful. Light movers are always going to help increase yields and more-evenly distribute the light to all of the leaves, and if you're pushing the plants with that much light putting the lights on a light mover is certainly recommended. You would need at least 2 light movers for the 4 lights though, running parallel to each other.
      For a 5x5 veg area, the single PhytoMAX 400 will work great, 2 PhytoMAX 200's would provide basically the same amount of light but would more-evenly distribute it. For 2 PhytoMAX 200's to cover the area though, you would need 2 light movers running parallel to each other to get even coverage.

      Reply
  • Tray

    Just wanted to say Thank You for the concise and helpful information on this site. Have grown two crops, Mixed Strains (Try Pineapple Chunk, EXCELLANT!), of Auto Flowers, with a 1000 and a light mover in soil and a 5x5 Gorilla tent. Yields really top notch and quality as good as I've gotten at a Colorado Rec Disp., (Drove there from Out of State). Researched a majority of the LED lights available and Thanks to several different Review sites, weeded out, (Sorry), the Reality from the hype. I am 60 years old. Thanks for all the info. as it was really helpful. Tray

    Reply
  • QCOB (quintessential cheap old bastard)
    QCOB (quintessential cheap old bastard) August 1, 2016 at 11:25 am

    What is the D L I for tomato plants or how / where can I find out ?

    Reply
    • Kevin

      Hello,

      The minimum DLI for growing tomato plants is 15 μmol/m2/s, although 20 or more is recommended. It is important to note that tomato plants require at least some dark period every day, unlike vegetative Cannabis plants. If tomatoes are given continuous light (24 hours per day) the plants turn yellow and stop growing properly. 4 hours of darkness per day is enough to keep tomatoes growing happily.

      With our lights running 20 hours per day, you'll get great results growing tomatoes under the following footprints:

      PhytoMAX 1000:
      Minimum recommended DLI: 6 x 6 feet (hanging height 35 in.)
      Medium DLI: 5.5 x 5.5 feet (hanging height 32 in.)
      High DLI: 5 x 5 feet (hanging height 29 in.)

      PhytoMAX 800:
      Minimum recommended DLI: 5.5 x 5.5 feet (hanging height 32 in.)
      Medium DLI: 5 x 5 feet (hanging height 29 in.)
      High DLI: 4.5 x 4.5 feet (hanging height 26 in.)

      PhytoMAX 600:
      Minimum recommended DLI: 5 x 5 feet (hanging height 29 in.)
      Medium DLI: 4 x 4 feet (hanging height 24 in.)
      High DLI: 3.5 x 3.5 feet (hanging height 20 in.)

      PhytoMAX 400:
      Minimum recommended DLI: 4.25 x 4.25 feet (hanging height 25 in.)
      Medium DLI: 3.5 x 3.5 feet (hanging height 20 in.)
      High DLI: 3 x 3 feet (hanging height 17 in.)

      PhytoMAX 200:
      Minimum recommended DLI: 3 x 3 feet (hanging height 17 in.)
      Medium DLI: 2.5 x 2.5 feet (hanging height 14 in.)
      High DLI: 2 x 2 feet (hanging height 12 in.)

      Reply
  • Jack

    wondering what square footage and which one of your lights I should use to veg and flower 10 cannabis plants. Thanks!

    Reply
    • Kevin

      Hello Jack,

      It all just depends on the size of the 10 plants you're planning to grow! Our PhytoMAX 200 light covering a 2.5'x2.5' area (about 6 square feet) will work great for a sea-of-green style grow, where you flip the plants into flower when they're very small. Check out our cabinet grow with a PhytoMAX 200 for an example of this style of growing- you can get a lot of bud out of a small space!

      If you let the plants get 12-18 inches tall and top / trim them a bit to encourage bushiness, our PhytoMAX 1000 covering a 5.5' x 5.5' (30 square foot) area could also work, and easily yield 1-2 pounds of buds per harvest. Any of our light sizes in between would also work, with the plants being flipped into flower at an appropriate intermediate size. If you veg the plants for longer to get them bigger, you could even need 2 or more PhytoMAX 1000 lights, though we generally recommend flowering smaller plants for several reasons. Growing huge plants in veg will yield much more bud per plant in the long run, but in the extra time it takes to grow the plants large, you could already have had a harvest with smaller plants. Larger plants are also generally harder to care for, especially in terms of staking and pruning.

      So which of our lights is best for you really just depends on what your yield goals are, how much space you have, how much electricity you want to use, etc. If you have any questions, you can always give us a call at 720-420-1209 and we can help find the right size light for your needs.

      Reply
  • Dana

    Hi, I'm thinking about purchasing either a 3x3 or a 4x4 grow tent for cannabis and I would like to know what you'd recommend. Would the PhytoMAX 400 be insufficient or would the 600 be too much? Thanks!

    Reply
    • Noah

      Hi Dana, thanks for the question. For a 3x3 we would recommend using a PhytoMAX 400. For a 4x4 you would want to go with the PhytoMAX 600 or the PhytoMAX 800. They would both work very well, it just depends on how much yield you are looking to achieve. These answers are assuming you are talking about flowering in these tents. If you are going to veg and not flower the you could use smaller lights.
      Happy gardening,
      Black Dog LED

      Reply
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