Indoor Marijuana Grow Lights

indoor marijuana grow lights

Indoor marijuana growing requires the use of Grow Lights designed specifically for indoor plant growth to replicate the lighting that the sun provides for outdoor plants. There are many different grow lights available, all of them using different spectrums to produce different growth in marijuana plants.

How Many Grow Lights are needed to Grow Medical Marijuana

The minimum amount of light required by marijuana plants is around 3000 lumens per square foot. However, it’s not 100% accurate, since although you may have a 10,000 lumen light, the amount of light that reaches the plant varies with the distance between the light and plants, and reflectivity of the grow box. The ideal amount is somewhere around 7000-10,000 lumens/sqft, and as long as the plants do not burn, as much light can be used as you want. (*note, the sun produces about 10,000 lumens/sqft, on a sunny summer day).

Determining lumens for your grow area:
Determine the square footage of your area (example in a 4 foot by 4 foot area, there is 16 square feet)
If you have a 1000 watt High Pressure Sodium Grow Light, that produces (approx.) 107,000 lumens.
Divide this by 16 (your square footage) 107,000 / 16 = 6687 lumens per square foot.
So just divide the total amount of Lumens, by the total amount of Sq ft, and thats your lumens per square foot.

How far away from my plants do the grow lights go
The marijuana grow lights in your indoor grow room should be as close as possible to the plants without burning them. There is no such thing as too much, unless there is sufficient heat to dry out and burn the leaves. A good rule is to put your hand under the grow light, if its too hot for your hand, chances are that the plants will be too, so move the light up until your hand feels more comfortable. For seedlings and clones, I keep my Fluorescent shop lights a little further away from the light, because they are very susceptible to burning and drying out, at these stages. Efficiency is very important when choosing a type of light. The wattage is not the most important thing, as you can see below, different types of grow lights produce different amounts of lumens per watt. A 300 watt incandescent will produce about 5100 lumens. While a 300 watt Metal Halide (just an example, they do not come in 300 watts), will produce 27,000 lumens. Obviously far more efficient for growing, while still using the same amount of electricity.

Approximate light production:
Incandescents: 17 lumens/watt
Mercury vapor: 45-50 lumens/watt
Fluorescents: 60-70 lumens/watt
Metal halide: 90 lumens/watt
High pressure sodium: 107 lumens/watt

Incandescent Grow Lights

Incandescents are the most popular type of lights in the world. They may come advertised as incandescent, tungsten, quartz, halogen, or simply standard. The important thing about incandescents is this: they suck.
There are some incandescents which are sold as ‘grow lights.’ They usually have a blue coating and usually come in 60W and 120W sizes. While they may seem like a good choice to new growers, they are next to useless; they produce some light at a usable spectrum, but only have about a 5% efficiency and generate more heat than usable light. Most of us have these in our homes right now. Don’t use them for growing, instead opt for a Compact Fluorescent as a cheaper but more efficient alternative.

Fluorescent lighting

Fluorescent Grow Lights are a lot more useful than incandescents. Their efficient enough, and cheaper than HID lights. Compact fluorescent tubes are popular with growers because of their good output to size ratio. Compared to standard 4′ tubes, compact fluorescent bulbs are smaller, and more can fit into a given area. Fluorescents are good for small cannabis grows on a tight budget, and for novice marijuana growers, since they do not require any special sort of wiring or understanding of the necessary bulbs for a given fixture, and are very widely available. Fluorescent grow lights come in many different Kelvin ratings; often the spectrums are labeled on packaging as being ‘cool white’ or ‘warm white.’ Cool white is more blue, and is good for the vegetative stages of growth, and warm white light is more orange or reddish, and is best for the flowering stage.

High Intensity Discharge (HID) Grow Lights

Mercury Vapor (MV) Lighting
Mercury vapor lights are not the most efficient light for growing. They are very bright, and relatively cheap. They do emit light at the wavelengths necessary to support your plants growth, but not nearly as good as a MH or Hps light. Much of the light emitted by MV lights is bluish-white. Street lighting is what most MV lighting is used for.

Metal Halide (MH) Lighting
Metal halide lighting systems are optimal for use in the vegetative phase of growing. They emit mostly blue light, which encourages vigorous growth of foliage. They are very efficient, but can get rather expensive to start with; fluorescents may seem more appealing because of their lower price, and they are not much different when compared on a lumen-to-lumen cost level. These lights can be used through-out the grow, but will most likely result in light, fluffy buds.

High Pressure Sodium (HPS) Lighting

High pressure sodium lights emit mostly orange, yellow, and red spectrum light, which is perfect for the flowering stage of the plants growth. They are (in my opinion) the most efficient type of light available for any application. HPS lights can be used through-out the entire grow. They produce more dense and usually larger buds than any other light.
HPS lights are generally a little more expensive than MH systems of similar wattage. They are more commonly used by experienced growers because of their ability to produce tighter buds, higher lumen-output-per-watt, and will produce from start to finish.

Fluorescent Lights
A fluorescent light is made up of a glass tube coated with phosphor, which is filled with a mixture of gases. When electrical current is applied, it “excites” the gases, causing the tube to glow brightly. ie: to “fluores”. The tubing is coated with phosphor, which will determine the color of the bulb. There is a wide variety of lengths from 6 to 96 inch, the most widely used is a 48 inch fixture. Fluorescents come in a wide range of watts any where from 4 to 214 watts that I have found. Fluorescent tubes are rated by hours, these hours vary by the manufacture, the most common rated hours are from 6000-22000 hrs.

What are lumens?
Lumens are the unit of measure that state the amount of light output produced by a light source. The higher the lumens, the greater the light output. The standard fluorescent tube should produce at least (3000-3300) lumens.

How can I optimize the light output?
You can help reflect the light out of each tube, by using metal foil tape as a reflector, attached directly to the tube. For more info on lighting and different lights please visit our Grow Lights section.

37 comments… add one


  • If I use the same watt MH bulb, can I use the MH bulb in a MV ballast? 175 watt MV ballast.
  • Hi, Im a new grower and I would like to start off with 3 very small plants. Two questions: In your opinion, what is a good soil mixture? (and must it be replaced over a certain period of time) also, any tips on controlling the overall size of the plants?
    • author
      fox farm makes a good soil for growing. replace it every time u start a new plant. if u want big plants, cut them while they are in the veg stage and they will branch out. if u want small plants, start flowering them immediately after the clones root (this will keep them short)
  • One question, since i have a limited amount of head space for the plants, and i want to bud them small, how do i put them into flowering stage straight after vegetative growth ? And whats the range between them two ? Your answer will be greatly appreciated.
  • Hi Drizzle, I have a 8 W x 7 L x 8 H (448 sq ft) room which will be utilized as flower only. My Present Equipment: Ballast= two (2) dimmable 1000 watt (1000, 600, 400) Reflector= two (2) Adjust-A-Wing (large) with super spreaders Exhaust Fan = Inline 8" (747 cfm) Oscillating Wall Fan= two (2) 16" CO2 2 Generator= 2 burner (each burner rated @3 cf hr) with electronic ign. De-Humidifier= 65 pint My questions are: 1) Would you keep this c02 generator or purchase c02 regulator and bottle ? 2) It is my understanding that higher temps can be utilized when using c02. Is this correct ? 3) Can I run a sealed room and vent only as needed (temperature) using the c02 Gen. and using your recommended Humidity/Temperature Controller ? 4) What Temperature Range with c02 Gen vs c02 Reg + Bottle ? 5) What Humidity% Range with c02 Gen vs c02 Reg + Bottle ? 6) Your recommendations for an intake fan ? Thank You Kindly for your time as it is much appreciated, ETak
    • author
      first off, your room is 56 sq ft. (dont add the height, thats for cubic feet).. anywho, the most you would need is a bottle. generator is too much for that small of a space..unless u plan on expanding in the future... higher temps are worse for the plants when co2 is present. a mixture of high temp and co2 can easily burn the plants. you can run sealed room and vent, just use any of the multi timers i have listed in the grow store. I personally use green air products. keep room in the 75-80* temps.. humidity around 20-30%. intake fan i love the hydrofarm 8". super quiet and powerful.
  • do i need a co2 output for about 80 square feet, approx 40 plants? or can i get away with just having a couple of smokes in there?
    • author
      i prefer Co2. that small of a space should be just fine with fresh air intake. enough Co2 in the fresh air to easily keep that size room filled.
  • I have three clones right now and a grow tent which is in my closet and i have one led light and pots soil and nutrients is thier anything else i need in order to have the most succsesful grow as possible
  • i burnd my plants due to many lights not all of them burnd i was just woundering how would i got about bring them back cuz there not completely burnd
    • author
      try removing any burned parts/leaves... raise the lights and use less nutrients until they come back.. if they got too stressed, they wont come back, but its worth the try
  • hello! Im starting up a grow room( 40-50squar feet) about 100-150 plants. Some one who have a set for sale. But only the best. Much apprishiaded for tips our a list of products I will need! thanks
  • Hey dizzle. Im the one who commented on your harvesting process thingy with the videos on how to trim and dry and stuff...But now I want to know if there is any way I could get those kinds of lights or similiar lights in a regular store like walmart, krogers, or wallgreens... Stores like that. Thanks for everything
    • author
      no, none of those stores have those lights... u can buy shop lights (flourescents) for cloning at home depot or lowes, but all other grow lights are best bought at grow stores.
  • For a CFL over an Ecogrower 6 in Veg growth would one be best to go with a 6500k bulb or run a 25,000k Sunblaster? Would you go the 150 watt or step up to a 200? Thank you.
    • author
      depending on your climate, most people will leave on all day on a minimum drip, or on for 30 mins off for 1 hour. when i personally used drip (with rockwool) i set mine for 30 on 30 off. worked well for me. ")
  • how come some of my plants are reaching for the sky in dark time when the others plants are relaxing?
    • Because plants stretch when they are trying to reach the light source. The same thing happens if you are using florecent lighting and your seeds or cuttings are not close enough to the light - they become thin, dainty, and stretched out. If you would like to prevent this, re-arrange your plants each time to water. If you are in the middle of the grow you can pinch the stem and bend the top few inches of the palnt over, which will shoot the hormones down the plant, and encourage other branches to reach for the light lower down the plant, which will not only keep the tops of your lights out the plants if they are stretching, but also increase your yeild per square foot. But again, it is becuase the plants are stretching attempting to reach the lights source. The plants directly under the light are getting plenty and are satisfied with their growth rate, keeping their nodes closer together, and depending on the strain, some people (including myself) using pinching and arranging plants to control the stretch and height of the plants to zero in on the most optimal structure for that plant to produce as much quality as possible.
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  • Once I change my light cycle to 12/12 how much bigger should I expect my girls to grow. I'm trying to figure how much room I will need for flowering and when is too soon to start flowering? Thanks! True Planet
    • author
      depends completely on the strain, as well as how old they are when u start flowering them. most plants will grow 10-12"+ during flowering.
    • author
      u can get everything u need right here on the site under "grow store" i have already gone on amazon and found all of the best deals and organized them for easy use. u need a grow system, chemicals, lights, fans, timers, etc etc... go take a look at the store. watch the "videos" and then you will know exactly what to get for your situation. ;)
  • hi dizzle i am a beginner and need some help i have mad a box and lined with foil dull side showing and its 500x300 and 700mm tall is this enough for just one plant and what bulb should i use please thanks :-)