Marijuana needs light to grow. For outdoor growers, this is supplied by the sun but indoor growers need to replicate the sun in their grow room using marijuana grow lights.

In this topic you should come out with an understanding of the terms used in lighting, the types of marijuana lighting available for your marijuana grow room, and the light cycles you will need for the different stages of your marijuana plants life cycle.

Lighting Basics Explained

Lumens and Kelvin

The main terms used when people refer to light in marijuana growing are lumens and Kelvin, which are the brightness and warmth of light. Lumens are a measurement of the total amount of visible light and Kelvin is a measure of the color temperature the bulb is emitting. Light is comprised of separate bands of colors, with each color sending the plant a different signal and promoting different types of growth. These contrasting color signals mean you require different marijuana grow lights throughout the various stages of your grow.

Vegetative growth

You need a bulb that emits light from the blue end of the spectrum as it imitates the midday sun of summer. The recommended light will be 6500k.


When flowering your plant, you will need a bulb that imitates a similar light of Fall/Autumn, which is towards the red end of the spectrum. A bulb that is 2700k will be suitable for flowering.


Brilliance is used to discuss the clarity and the sharpness of the light as it gets further away from the source, or in this case, the bulb. As you get further away from the light source, its brilliance deteriorates. This affects how far away you keep the plant from your marijuana grow lights:: too far away and you’ll stretch and weaken your plants; too close and you’ll burn and damage them.


The wattage you use affects the amount of space your light will cover; the higher the wattage, the larger the surface area covered. For example, a 1000 watt bulb lights a larger surface area than a 600 watt bulb. The type of light you are using and the amount of space you are growing in will affect the amount of wattage you will need.

image of light Kelvin - Marijuana Grow Lights: Fluorescent VS CFL VS LED VS HID VS MH VS HPS

What types of marijuana lighting and equipment are available?

This section will explain the different lighting options available, how to use them, as well as very basic pros and cons.

Fluorescent Tubes

What are they?

Fluorescent tubes are long glass tubes filled with inert gasses. They come in a selection of lengths and are available in a variety of different color spectrums, emulating the spectrums found in sunlight. Most growers use fluorescent tubes on clones and to maintain mother plants. They can be used for flowering, but the buds and yield will be poor, making it not worth your while. Also, the light brilliance from fluorescent tubes degrades rapidly.

Best practice:

To get the most out of fluorescent tubes, you will need to keep them 6-8 inches away from your plant. They are good for use on clones and seedlings or for vegetative growth. Try to avoid using them for flowering.


$80 for T5 Grow light 2 Tube – $220 for T5 Grow light 8 Tube.


20,000 hours.


-Excellent for seedling and clone growth.

-Low Running Cost.


-Not good for flowering.

-Bad light penetration.


What are they?

Compact fluorescent lights or CFLs are similar to standard fluorescent tubes, but are smaller in size and boast increased power. They are available in both daylight (6500k) and warm/soft light (2700k) and generate very little heat so are ideal for smaller grow spaces.

Best practice advice:

If you’re using CFL’s as your weed grow lights, you are better using more, lower wattage bulbs to spread the light around the plant. You will need to keep CFLs close to your plant as they a have poor light brilliance. Increase your light coverage and penetration by hanging lights around the side of the plant.


20,000 hours

What are the Costs?

$40 for a 100watt bulb.


-Good for small grow spaces.

-Low running cost.

-Do not require ballast.

-You can get them from home depot.


-Not suitable for larger grows.

-Lack penetrative power so need to be kept close.

LED Grow Lighting

What are they?(LED Grow Lighting)

Unlike HID lights LED lamps contain no filament to burn out and therefore have an extremely long lifetime, making them an ideal hydroponic lighting choice. For many, LED lighting is seen as the future of indoor growing as it has extremely efficient running costs that are a fraction of HID and CFL lights while generating very little heat.

Best practice advice:

LED grow lighting runs at a very low heat, meaning you can grow your plants right up to the light without overly worrying about heat burn.


60,000 hours

What are the costs?

$100-$600 dollars for 400watt HID equivalent.


-Extremely efficient.

-Lamps are at a fixed angle so all light is directed at the plants.

-Run at low temperatures.

-Long life.


-A little expensive.

-Currently do not produce the same quality weed as a HID marijuana lighting set up.


What are they?

HID or High-Intensity Discharge lamps are the most common type of marijuana grow lights used for indoor growing and are arguably the most efficient way of producing good yields indoors. The HID family includes Metal Halide (MH) and High-Pressure Sodium (HPS). HID lamps produce the perfect spectrum for both the vegetative and flowering stages of marijuana growth.


What are they?

MH or Metal Halide is currently the most efficient source of artificial white light available to indoor marijuana growers for vegetative growth. MH bulbs come in a range of watt sizes, including; 175, 250, 400, 600, 1000 and 1100. The most popular with indoor growers are the 400-600 watts.

Best practice advice:

A metal halide bulb’s light spectrum and 6500 Kelvin temperature are perfect for the vegetative growth stage of your marijuana plant. MH bulbs have excellent light brilliance but produce a lot of heat.


10,000 hours.


What are they?

HPS or High-Pressure Sodium is an extremely efficient bulb that emits an orange light spectrum, mimicking the sun of fall/autumn (2700K). Like MH bulbs, HPS come in a range of watt sizes. The most popular with indoor growers are the 600 watts.

Best practice advice:

To get the best out of your HPS bulbs, use for the flowering stage of your plant’s life cycle in conjunction with an MH bulb, with the most efficient ratio being 1 HPS for every 1 MH.


10,000 hours.

What are the costs?

Average Cost incl. ballast (need to have specific costs inserted)

400 watt MH lamp – $85 – $120.

400 watt HPS $25 -$40.

400 watt Ballast $175.


-Excellent marijuana lighting for bud production.

-Excellent Spectrum.

-Still the best light sources for indoor grow.


-High electricity bill.

-Run at high heat.

-Short life in comparison to others.

A guide to maximizing your marijuana grow lights using specialist reflection equipment:

Reflector Hoods

Reflector hoods make your bulb more efficient as they reflect light back towards the plant. An effective horizontal reflector hood increases the amount of light coverage and brilliance your weed grow lights produce, helping to produce bigger yields. The closer you move the hood to your bulb, the more light it will reflect. This, in turn, generates more heat which growers need to be careful of as it can cause your plant to suffer from heat burn. Open-ended hoods dissipate heat quicker as do those made from aluminum. To increase cooling, aim a fan at the light hood to circulate air around the bulb.

Grow Room Reflection

Using reflection helps get light to the lower parts of the plant, increasing your overall bud production and making your grow room more efficient. There are many different types of reflective materials available for your grow room with the best two listed below. For more examples, please view the Grow Room section.

  • Mylar– Is the preferred reflector of choice for most indoor growers as it reflects almost all light from your marijuana lighting when laid flat against the wall. Cover staple or nails with tape to prevent ripping. Flat white paint
  • Flat White Paint– Contains little or no light-absorbing pigment and therefore reflects a large amount of light. Use a matt texture as it reflects more light.

What is ballast?

Ballast for marijuana lightsBallast is used in conjunction with an HID lighting set up. Ballast is a transformer that alters the electrical current used by your bulb. A smart grower will buy their entire HID system at the same time, including, lamp, ballast, socket, connecting wiring and timer. If you do not match the ballast with the bulb, you either run the risk of having inefficient lighting or burnout, which could result in you losing more than your marijuana crop! Ballasts run between 90 – 150°F, so make sure they are not placed on anything flammable.

Bulb Proximity

Plants need around 10,000 lumens for maximum growth and yield. The table below will tell you how far you should be keeping your light bulbs above the plant.

Light Cycles

A light cycle is the amount of light and darkness within a 24 hour period. Throughout its life, your marijuana plant will require different amounts of light depending on what growth stage it has reached. Having your plant on the correct light cycle is important if you’re going to grow good quality weed. Putting your plant on the wrong cycle can put it under stress resulting in a hermaphrodite plant and small amounts of weak marijuana.

You can use the following table to see what light cycles you should be on for the various stages of your marijuana plants life cycle, to help ensure you’re getting the most out of your marijuana grow lights.

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