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What Is The Best Marijuana Grow Light Setup For An Indoor Garden?


marijuana cannabis garden lighting lightsHow To Optimally Place Your Marijuana Grow Lights

How Grow Lamps Function

Except for the top and bottom of the arc tubes where obstructions are located, the construction of grow lamps enables light to go in every direction. Artificial light production is brought about via agitation of the chemicals, which occurs in a high-voltage vacuum tube. The glowing of these chemicals allows light to come from its source at 360 degrees.

This obstruction blocks light, meaning that just half the light is coming out at the end as compared to six inches to the side. This is determined with a light meter. This is caused by particles that are near the glass arc tube at the time of agitation.

Reflecting Light Correctly

The reflection of light is very important for creating an ideal environment for your plants to grow. Therefore, the location of the wall that creates this reflection is also of great importance. A reflective wall is necessary for capturing the growing area’s light when your room space is bigger than your growing space – otherwise you would need to light up the rest of the room as well as the walkways. This is clearly a waste of electricity. You can use Myler or other silver, shiny products for your reflective wall, but a reflective white paint is favored by most professionals. Make sure to download my free marijuana grow bible at this link and grow like a pro!

For ebb-and-flow gardens, it’s important to set up your reflective walls just 6 inches away. Because the width of ebb-and-flow tables is usually four feet, putting up reflective walls at this distance still allows for airflow, as well as the bushing out of your plants. You’ll need to set up your reflective walls a bit differently if you would like to grow plants that are bigger. Do it at five-foot centers per 1000 watts. For example, use a single light if it’s 5×5 feet, 10×5 feet should have 2 lights, 15×5 feet should have three, 10×10 should have four, etc.

The air-cooling of such lights allows for hot air’s removal, taking it away from the growing area. At the same time, a loss of light is avoided because of the reflective, white-colored walls.

Maintaining the Efficiency of Your Lighting

You should make sure there’s an equal cover of light across your entire garden to properly set up your lights. You can use a light meter to ensure that no hidden hot spots exist.
Another easy way to test the intensity of your lights is simply through feeling with your hands. Leave your bare hands where you plan on placing your plants. If you’re unable to keep your hands there for long due to the excess heat, it’s a good indication that your plants also would be uncomfortable with such lighting. To put it simply, as a rule: Whenever you’re uncomfortable in the grow area, so are your plants. This includes temperature, humidity, ventilation, and so on. If you don’t correct this, you will definitely have a smaller yield.

One important fact to note is that some light (10%) can easily be lost simply by choosing to burn your lamps horizontally. The lamp also can lose 25% of its lifespan, meaning that to achieve the highest light output, lots of growers will simply change the light after just 75% of one year’s usage.

For horizontally placed lamps, two-thirds of the lamp’s light emissions bounces of the reflector, while just one third goes straight to the plant canopy. Losing light because of the quality of the reflector’s material can also occur; if it’s 92% reflective, you’re losing even more light – 8% in addition to the two-thirds already lost. Reflectors with built-in glass lose a further 3-5% of light.

For more specific numbers: 100 watts would be lost per 1000 watts (10% loss), and 666.66 watts of light (two-thirds of 1000 watts) are being affected. Therefore, losing 8% and then another 3% means 11% loss of 666.66, which is 73.33 watts. Adding the original 100 watts to that means that, in total, 173.33 watts of light are being wasted. In other words, nearly one fifth of the yield is ruined simply because of the orientation of your lamps.

Wave cancellation is another factor that can cause light loss due to horizontal lighting. Wave cancellation causes the loss of light when it is bounced back at itself. It can be confusing because light seems to be continuous, given the fact that its bandwidth is extremely small (only nanometers), and its creation is at time intervals invisible to the naked idea.

Although we know that there is a clear light loss when it is redirected into itself, we do not know exactly how much this is. Another factor is the elements used in lamps, where their agitation from electricity (especially salts) occurs. Simply put, expensive artificial light should not be wasted. This gives a high value to light meters, as well as the optimal positional of lamps.

For a rough guide for light placement, see below.

Type of light: distance from plants

LED: Very near
Fluorescents: Three inches
Compact Fluorescents: Three inches
Sulphur Bulbs: Eighteen inches
Induction Lighting: Fourteen to eighteen inches

To find out more about LED grow lights, click on the banner below:


High-Intensity Discharge Lights:
1000 Watts: Twelve to eighteen inches
600 Watts: Eight to sixteen inches
400 Watts: Eight to sixteen inches
250 Watts (or lower): As close as possible

Learn more about marijuana grow lights and download my free marijuana grow bible at this link here

Which Lamps Work Best for Flowering Cannabis?

The easiest to find and most reliable lamps are HPS (high-pressure sodium) and MH (metal halide) lamps. You’ll start to see obvious differences with types and brands as you experiment with the variety of choices and get nearer to picking one source of lighting. The plants located in between the lights often end up being the healthiest and highest quality plants. You will see major differences in the growth and quality of the plants as you move further away from the central light footprint.

The sun has a reddish cast at sunrise and sunset. Because HPS lamps are strong in the red spectrum, they “wake the plants up,” or stimulates them to begin working every day. The sun’s color changes to blue as the day continues, and when the day ends the sun returns to its red color. The spring and fall sun has more red in the early morning, and during the early summer the colors are more bluish early in the morning. All these colors encourage plants to begin growing and flowering accordingly.

You can spot this reddish hue when the sun is rising or setting. This reddish hue stimulates plants and makes sure they adhere to the changing seasons (i.e. dry or wet season), as well as the length of the day. Because of plants’ evolution over hundreds of millions of years to adapt to this natural phenomenon, it’s important to try and replicate it as exactly as possible. The daylight 5K metal halide lamps give off the best type of light for growing (vegetating) plants. It will help leaves to come out healthier and larger than when MH lamps are used. A common misconception among many growers is that there is no difference between MH lamp output. In fact, a difference does exist; one example is the MHS 125,000 MH/U universal position or MH 90,000 initial lumens output.

Additionally, it is better to use six T5 fluorescent tubes for the vegetative growth of plants, as compared to MH lamps with 400 watts. The color spectrum of T5 lamps is better than MH, and they also have a less drastic difference between the night and day temperatures. The lighter time (day) should, of course, be a higher temperature than nighttime. To make it ideal, there should be a difference between light and dark temperatures of approximately ten degrees Fahrenheit. If this is not done, “stretching” (extra elongation) between internodes will occur, meaning the plants will grow to become tall and lean rather than short and bushy.

Preparation of Your New Light Setup

Make sure you always have the behavior of light at the back of your mind when planning a lighting scheme: how it travels, how it reflects, and how it bounces around the area of growth. Remember the importance of equal light distribution when using more than one lamp; otherwise your plants will grow in a variety of ways since they will receive varying amounts of light. Plants that receive the same amount of light will grow quite similarly.

You should also remember to grow your plants by starting with cuttings or seedlings that have even and consistent growth. Never start with differently sized plants under the same light, since getting them even light and growing them at the same rate would then be nearly impossible. If you grow seedlings and cuttings side-by-side, cuttings will generally grow faster and larger than seedlings. Avoid this by keeping clones and cuttings the same size, and only choose cuttings that look similar when rooted.

Check the equality of distribution of your lighting even before you put your plants in the growing area. Do this with a light meter. Simply bring it under where the two sources of light meet, and change the location of the lamps until you are sure the light is even everywhere. Keep in mind that this is easier to accomplish with vertical lights than with horizontal ones. Do not forget the importance of heat, as well; lights give off heat, so it is especially important to be aware of this factor when using extra lights. If not, you could cook your plants’ growing tips.

Simply put your hands underneath the lamp (where the plant canopy will be located) and see if it becomes uncomfortable after a couple minutes. If so, your plants would be uncomfortable too – but unlike you, they can do nothing to escape such discomfort. An inverted “V” is located in almost every horizontal reflector. Its purpose is to keep light from reflecting again through the arc tube, bouncing back on itself, and disappearing. If you try and think of one light beam’s size (1/10,000th of a human hair), then imagine the many beams of light and the fact that this means some of them will surely be canceled when they reflect.

Growers must try to keep this from occurring. It would indeed be a challenge to set it up in a way to achieve a 100% bounce back, given one beam’s minuscule size. Make sure to download my free marijuana grow bible at this link and grow like a pro!

Advice on Horizontal Lighting

A: This defines the light’s strength. There would be a lack of light above this line due to its reflector, which directs the light toward your growing area. If one is not in the stream of light, it will begin growing incorrectly due to its lack of light.

B: There are multiple lamp systems, and they should be correctly place so that the top or your plants all receive the same amount of light. Uneven growth can occur when equal light distribution doesn’t exist, and that perpetuates the difficulty of keeping your garden well-lit.

C: Any light that travels all the way down to the garden has to have an equal strength as compared to B, where the two beams touch. As mentioned above, unequal distribution will cause unequal plant growth.

D: Grow room lights’ location also matters. You can place them further away from the reflectors than you can from the reflective wall, where we would like to bounce the light off of. Therefore, to achieve even lighting, place the light closer to the wall than the middle of the room.

E: Lights can be a bit further apart from each other since it is unnecessary to bounce light off of a reflective wall. Make sure he reflector’s edge is 12 inches away from the wall and 24 inches away from each reflector.

Using Light Patterns as a Placement Guide

If you’re deciding between horizontal and vertical reflectors, simply use the light footprint. Horizontal reflectors focus the light in a smaller area than vertical ones! Although you might assume this means there would then exist about two times the light in the growing area, it’s important to note that the horizontal light actually is losing light simply from its position and material. They do give off more light per square foot, however – about 1.3 times more than from a vertical reflector. A vertical setup, on the other hand, would provide about twice the area.

Note: every calculation for 3 watts per square foot are from vertical lighting. We also must keep in mind how light leaves the arc tube – it goes in 360 degrees, but, of course, cannot get through the obstructions on either side of the tube. Therefore, a very small of light goes through the ends, which consequently alters the light concentration.

The Production of Light

As mentioned above, light comes from a combination of specific chemicals that are electrically agitated inside of a vacuum tube. The chemicals then begin to glow, creating the light that has a 360-degree pattern. Because of the existence of millions of such chemical elements in the arc tubes, light is formed in all directions – excepting the ends. Regardless of whether the chemical is near the surface or near the middle of the tube, they will all produce light in 360 degrees. Plants take in light from all directions due to this continuous distribution of light. Of course, light cancellation will still exist to some degree, but it will not stop growth. Rather, it just provides an unavoidable challenge when setting up your lighting.

If you want to start growing, download my free grow guide and order some marijuana seeds. All top quality marijuana seeds are available in my marijuana seed shop. We ship seeds to the US, CA and many other countries. For any growing related question please visit the marijuana support page.


About Author

Robert Bergman is a master marijuana grower. Robert Bergman is the author of 'Marijuana Plant Care' and 'The Marijuana Grow Bible'.


  1. sarah roberts on

    I will be using two 400 watt hid bulbs this year. What is the light footprint for that?

  2. A hydroponic box is an alternative to growing plants on soil.

    It is generally put to use when there is a lack of space in a living area or a place with small vicinity. It is used to grow small plants like marijuana when the outdoor weather conditions aren’t suitable. It is a box like enclosure that uses water as the base that contains minerals and necessary nutrients that aids to a plant growth.

    Go through this one to know more of these hydrophobic boxes..

  3. I like the idea of feeling for the heat with your own hands. Too often, things like this get complicated and everybody looks for methods that are complicated or require a device of some sort, simple but effective is always better. Plus, if you’re hot, your plants will be too.

  4. Not Anonymous on

    I dunno how people are putting 600w 15 inches from canopy- thats super high lux- I was under the impression that 30k-50k lux was the highest you want for veg.

  5. I personally could give a fuck less about Robert or his business. I feel bad suggesting his company to a friend that made me look bad in the end. If Robert didn’t want his “stealth” method out there then he should have thought twice about fucking over someone. What’s fucking funny is you don’t even address the fact my friend did not get what she paid for.

    Furthermore, I have no loyalty to any company nor do I have any reason to aimlessly bash another company as I do not compete with them. I have purchased plenty of seeds with no where near the hassle my friend is dealing with. My friend purchased them back on Feb 5 and they still do not have any order to this day despite Robert’s company claiming to have sent out replacement seeds twice with the most recent one being shipped May 1.

    So if you wouldn’t bat an eyelash at 30-45 days, would you at 90 days because that is how long the original shipment was sent. So two shipments have been sitting there well after 45 days. Now does my friend have your permission to worry or should I just take this as Robert doing damage control under a fake account?

  6. Thanks for publicly revealing a company’s stealth methods to law enforcement. No one should sell you seeds, ever. Go breed your own. Also, It’s obvious you are a shill, a fool or a child. You wrote a paragraph about someone else’ situation, which makes it all seem less than genuine. Not to mention, be patient. It’s pretty obvious that you have never purchased seeds before. I wouldn’t bat an eyelash not seeing a seed order come in within 30-45 days. As they told you, it’s probably sitting in customs. Worry after 45 days, or if you get a letter.

  7. I’m a first time grower will someone please guide me to a blog for beginners or answer a few questions , these are white widow 5 1/2 weeks on 12/12

  8. I signed up for the ‘The Marijuana Grow Bible’ yesterday and so far nothing has arrived in my inbox. Evidently it is just an e-mail harvesting operation.

  9. Chris Pieser on

    I would like to introduce you to our new 500w Plasma Grow Light which outperforms 600w HPS with 22% less electrical usage, 22% less electrical heat loading, 34% longer lifespan, 10-13% more total assayable cannabinoids with no annual lamp changes and a return on investment in one year. Full-Spectrum Light-Nutrition will always outperform one or two color LED’s if you compare the cannabinoid content. I would be please to show you the proof we have collected from the Master Growers that have been testing this technology for the past five years.

  10. Perhaps it is something to do with Safari because when I refresh, previous posts do not show but the last one I did remains. I’ll check another browser. Thank you very much for the heads up on this.

  11. You may simply have to refresh the page to see your post. I can see all of them just fine. You wrote about Robert and his seeds 21 minutes before this post and then 10 minutes later you wrote about it being deleted.

  12. I appreciate the information Robert brings but I doubt I would ever buy any seeds from him. I had a friend purchase 3 different strains (total of 50 seeds) over a month ago which should have arrived already and they emailed Robert and was told they were only at the 18th business day out and to give it more time. Sorry but mail travels 7 days a week even if there is a day it is not being delivered. So my friend is out their $250 and 3 strains and playing the waiting game to request replacement seeds to be sent which will probably take another month. A month waiting most likely means Customs grabbed them. Why make your customer wait even longer for something they already paid for? Wouldn’t it be wiser to keep the customer happy instead of telling them to wait for something that at this point will not likely be delivered? I suppose they could always initiate a chargeback for the “cell phone” they were told use as an excuse for their purchase.

    I am not knocking Robert’s business but letting others know the potential hassles and problems they could face when buying from Robert’s company. Hopefully Robert does the right thing and makes this customer happy.

    Before those discredit my post, here is the email Robert sent to them:

    (Name Withheld)

    Sorry to hear your order did not arrive yet. Thanks for letting us know.Your order was shipped out 18 business days ago. We expect your order to arrive any time soon.

    We are based in Amsterdam, The Netherlands. Shipping to the USA usually takes 12 business days, but sometimes it can take over 30 business days.
    A delay at customs is often the reason. Our stealth packaging sometimes confuses them. If your order doesn’t arrive before March 20th, please let us know.

  13. Yeah if I win the lottery I would consider solar storm’s money sucking black hole lights.

  14. Silly Rabbit on

    You’ll get biggest bang for buck as described …. If you want low heat and electric go with SolarStorm LED!

  15. “Arc” tubes are actually plasma tubes. The UV light emitted is absorbed by phosphors and re-emitted in the visible spectrum. CFLs and fluorescent tubes are examples. They contain small amounts mercury which produces UV.

    “Myler” is Mylar. Actually aluminized Mylar.

    The white paint should be titanium based.

  16. Is there a beginner blog on here or can either of you recommend one where I can ask some beginners questions?

  17. Silly Rabbit on

    OK but a lot of info:

    Use T-5 2 foot four bulb lights to get the girls going and then put under 600 watt ups or if you can afford put under 400 watt metal halide and when flower times comes bump up to 600 watt HPS.

    The 600 Watt HPS provides best value for the buck. And a 600 watt lite can grow area between 8-12 square feet total. Have at least two separate rooms, kne for veg work and other for flowers!

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