Best grow lights for indoor cannabis growing 101

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The Best grow lights for indoor cannabis growing 101. Lighting is one of the most important and complex aspects of indoor cannabis cultivation.In this article I would like to teach you everything about this subject, as simply as possible. You’ll know exactly what lamps and equipment you need, how many hours of light per day are best for your plants, and what role the light color and lumens play in selecting the right light source.

Best grow lights for indoor cannabis growing 101

Best grow lights for indoor cannabis growing 101
Best grow lights for indoor cannabis growing

Lighting is important because your cannabis plants convert the light into energy for growth using photosynthesis. Photosynthesis is almost the “metabolism” of the plant. It converts light energy into chemical energy, which in turn uses it for its growth. Decisive is the chlorophyll – because of its color also called “leaf green”. There, photosynthesis takes place.

Basically, the more lights  your plants have, the more nutrients they can process and turn into growth. You get a better crop  with thicker flowers and a higher THC content.

Simplified equation

CO 2 + light energy + water = sugar + oxygen

The plant absorbs CO 2 from the air , water (along with nutrients) over the roots and light energy over the chlorophyll on the leaves . Through chemical processes in the plant, everything is processed into sugar building blocks (from which the plant builds cells). Oxygen is released through the leaves as a “waste product”.

What lighting do I need for my grow?

So that your plants grow optimally, they need different color spectrum’s depending on the grow phase  . This means that you usually have to buy two different grow lamps . However, some grow lights (eg LED panels) can also be used for the whole grow, as they cover the entire color spectrum.

The color temperature is measured in Kelvin . In the growth phase 6500K are optimal. In the flowering phase, the lamps should have 3500K.

In the table below, you will see that there are different types of lighting suitable for cannabis cultivation. They all have their advantages and disadvantages. And the industry now offers almost all types of lamps with different color temperatures.

<a href=
Lighting for Indoor Cannabis Growing” width=”650″ height=”185″ /> Lighting for Indoor Cannabis Growing

growth phase

cannabis growth phase
Cool “bluish / white” light
Optimal: 4000-7000K

flowering phase

Cannabis flowering phase
Warm “reddish” light Optimal: 2700-3500K

Brightness (in lumens)

Another important factor in the selection of the lamp is the brightness (measured in lumens). The larger the area on which you grow, the more brightness is required to allow all plants to get enough light.

The absolute minimum lumen that you should use is 15,000 lumens / m² for the growth phase and 30,000 lumens / m² for the flowering phase . Any less than this candrastically reduces the growth of your cannabis plants. This in turn has a negative impact on your harvest.

In addition, with this low brightness, the distance between the lamp and your cannabis plant must be adjusted every day to guarantee maximum light output. Optimal is  30,000 lumens / m² for the growth phase and  50,000 lumens / m² for the flowering phase .

growth phase flowering
Minimum :
15,000 lumens / m²Optimal for high yield:30,000 lumen / m²
Minimum :
30,000 lumens / m²Optimal for high yield:50,000 lumens / m²

Problem with Lumens

A problem with lumens, however, is that manufacturers can trick growers with some types of lamps. Lumens refer to brightness that is perceptible to the human eye. Our eye perceives green and yellow light best.

Plants need a different color spectrum to grow , mostly bluish and red light. However, some people can not see red and blue light. 

Here a manufacturer can theoretically use yellow and white light, which for the plant are a “useless” color spectrum, but will increase the lumen value. The lamp is then brighter to the human eye but the plant gets no benifit from this.


The lumen value is only meaningful when comparing two lamps with identical color spectrum! For example, you can compare High Pressure Sodium (HPS) models or Metal Halide Lamp  (MHL)


 models with lumens, since they all have the same color spectrum. All other lamp types are evaluated differently.

LED panels can not be compared by means of lumens, since many light-emitting diodes are installed, all of which can be of different design and with different color spectrum.

Power (in watts)

The brightness of the lamp depends very much on its power rating (measured in watts). The higher the wattage, the more power it consumes. However, depending on the lamp design, there are differences in performance and the resulting brightness.

Distance from light
Distance from light

Each lamp converts the electrical energy into light and heat. Modern LED and energy saving lamps use far less power (watts). They offer the same brightness as HPS or MHL . Reason : LED lamps have a higher efficiency and produce more light and less heat than HPS or MHL. For this reason they are many times more expensive.

The classic HPS / NDL combo has the advantage that the lamps are cheap to buy. In addition, it is easier to select the right lamps for you, as the best lamps have been tested many times by hundreds of growers.


Due to the many experiences ​​of growers using the MHL / HPS we know that  (150W / 250W / 400W / 600W/ 1000W) are commonly used and it is easy to mach the chosen lamp to the correct Growbox, exhaust air and odor filter etc.

Below you will find typical lighting sets, which will help guarantee you a fat harvest!

What lighting for cannabis is there?

Here you can get a brief description of each lamp type. So you can better compare what is best for you.

Metal halide lamp (MHL)

A metal halide lamp is the classic in terms of Indoor Growing. It is used in the growth phase.

Metal halide lamp (MHL)
Metal halide lamp (MHL)


The manufacturers have super-optimized the models over the past few years and have improved their service life. Even if the life span is up to 2 years, an MHL should be replaced every 9-12 months, otherwise it will not work efficiently and loses its luminosity – provided you grow without breaks during the year. The lamps come with an E40 thread and are simply inserted into the reflector.

An MHL becomes quite hot during operation . Therefore, the lamp must not be too close to the plant . Otherwise the  leaf tips burn. The extra heat produced from the bulb must also be  extracted with a suitable exhaust air fan. A cooltube can help with heat problems.
Since an MHL is very cheap and the installation is extremely simple, the MHL is suitable for grow beginners . As a beginner you can start with a 150W model your first attempts. After 3-4 Grows you can switch to more powerful variants or try different types of lamps.

However, you need more powerful extractor fans to remove more exhaust air because of the extra heat. A larger exhaust air fan needs to be used. Particularly in the summer and in the roof-top apartments too high temperatures can be a big challenge . As an alternative, PL-L lamps help as they generate far less heat.


High Pressure Sodium Grow Lights (HPS)

A high pressure sodium lamp (HPS) is a tried and tested lamp for the flowering phase. It gives off rather reddish light and signals the plant to form the buds.

HPS Grow Lights
HPS Grow Lights

An advantage of HPS is its depth of light penetration . meaning the light reaches the bottom leaves very well. Bud growth is increased and your earnings are increased. The service life is 1 year (during a continuous grow a year), 

The lamp becomes hot during operation , so some distance to the plant is necessary. Otherwise you will burn the top of the plant. Also you have to pay attention to the extra heat. The heat must be removed with an exhaust fan. In case of high temperature problems a cooltube can help.

Due to its low price and long service life, an (HPS) is  perfect for grow beginners . As a beginner you can start with a 150W model your first attempts. After 3-4 grows you can switch to more powerful variants or even switch to other types of lamps.

PS: Combined High Pressure Sodium lamps (HPS) already exist, which emit both cold / white and warm / reddish light. They can be used for growth phase and flowering phase. I exclusively use HPS lamps for both veg and bloom.

Fluorescent Tube (LSR)

Fluorescent tubes (LSR) are particularly suitable for the growth phase. There are also models for the flowering phase.

Fluorescent Tube (LSR)
Fluorescent Tube (LSR)

A big advantage is that the lamps do not get hot and can get very close to the plants. Another positive is the low power consumption and the fact that they have no external ballast (one is already installed).

Unfortunately , LSR have a poor depth penetration and must be suspended even very close to the plants. They are  not suitable for larger plants , since there is hardly any light reaching the lower leaves. This is especially a problem in the flowering phase , where some varieties can sometimes become very tall. Overall, LSRs are weaker in luminosity compared to MHL or HPS.

Fluorescent tubes are especially suitable for the cultivation of young plants (up to 25cm plant height) and suitable for the veg phase. If you have a separate breeding room , an LSR is the perfect choice. Even outdoor grower with LSR can benefit from the power saving and low tech of the lamps using them before they are transplanted into the open.

It is important that the LSRs are operated with a high-quality reflector for the highest possible light output. That’s why it makes sense to buy an LSR fitting in which everything is installed.

When selecting the fluorescent tubes and fittings, you should plan approximately 350W / m 2 of area to get the maximum out of the LSR lighting. Your absolute minimum is 200W / m 2 .

My purchase recommendation is the T5 fluorescent. The reflector is directly installed. All the necessary components such as power supply, connection cable and ballast are already integrated. 

If you want to buy spare tubes, you need to pay attention to the color code. The color code consists of three digits and indicates which color spectrum and which color temperature the lamp has. For growth and flowering you need a different color spectrum.

Buy the following:

Growth phase : 860 or 865 (ca 6500K)
Flowering phase : 827 (about 2700K) or 830 (about 3000K)
Since the light of an LSR consists of several spectrum, a comparison with lumens is really meaningful only for lamps with the same color code (you can compare an 860 with another 860 by means of lumens).

Also pay attention to the fitting length for the fitting. The lengths are standardized and only certain performance variants are available depending on the length. For example, you can buy 549mm long LSR in 14 or 24W for the recommended Light wave.

Energy saving lamp (ESL)

Energy saving lamps (ESL) are particularly suitable for the growth phase. There are also lamps for the flowering phase.

Energy saving lamp (ESL)
Energy saving lamp (ESL)


An energy saving lamp is, in principle, nothing other than an LSR that is twisted. It is just as cool and can get very close to the plants . The life span of an ESL is very high and you do not need an extra ballast (already installed ). Compared to LSR, an ESL is a little more space saving and fits into a reflector thanks to the standard thread (E40).

As with LSR, the depth penetration is poor the lamp must be very close to the plant and is not suitable for taller plants. The distance to the plant must be changed at least once a day and leaves little room for maneuver. The overall performance is lower compared to MHL and HPS, so a pure ESL used with a “normal” height Grow box would probably not be worthwhile.

Absolute beginners using ESL tend to have rather low yields 0.2 – 0.4 g /per Watt dry weight.

For comparison: with HPS / MHL  possible yields for beginners are 0,5 – 0,7 g /per Watt dry weight.

Meanwhile, ESLs are being replaced by the far more efficient and more powerful PL-L designs. In addition, these are many times cheaper.

ESL are particularly suitable for small breeding rooms for young plants up to the second or third growth week. Grower with a very low grow room  (less than 80cm height), who plan a Scrog or SoG Grow, can also use ESL. Grow boxes with a height between 80 and 160cm perform better with PL-L models.

With the help of ESL, outdoor growers can also raise their small cuttings/plants while saving space and energy- before they are transplanted into the outdoors.

For beginners: For the flowering phase, ESL is only suitable for additional lighting if your “main light” does not reach all plants or the lower leaves. So you can illuminate shadow spots and increase your yield a little.
There are many ESL on the market. All high-quality models do not cost much. 

PL-L compact fluorescent lamps

PL-L compact fluorescent lamps are regarded as the “sexy” alternative to ESL and LSR . They are similar in design to standard T5 LSR, but they are bent U-shaped. They are very compact in design and take up even less space than LED panels. In principle, it is a further development of energy saving lamps .

PL-L compact fluorescent lamps
PL-L compact fluorescent lamps

Although the purchase costs for all parts are somewhat higher than with LSR, the spare parts, also the lamps themselves, are much cheaper. The depth effect is somewhat better than with ESL and LSR with the same efficiency.

Interesting are the reports of some Grower, that with PL-L grown cannabis is more aromatic than with NDL. This can be related to the better color spectrum. However, PL-L does not approach the light output of an MHL / HPS configuration. 

PL-L are more suitable for Grower with experience and best used with compact Grows (under 160cm Grow box height, up to 100cm plant height). They are especially suitable for Scrog or SoG Grows as they are extremely space-saving. DIYers and DIY enthusiasts will be pleased, as PL-L can be configured very flexibly . In addition, low-budget grower can look forward to super cheap replacement lights  (5-10 $). Also the electricity consumption is relatively low . In order to achieve good light output and depth effect, PL-L should be operated with a reflector .

When selecting the fluorescent tubes and fittings, you should work on approximately 200-350W / m 2 area to get the maximum out of the PL-L lighting. Eanything under 200W / m 2 is going to reduce your yield.

A tried and tested fitting is the Starlight from Prima Klima. The PL-L lamps from Philips are included. The fitting accommodates all necessary electronics and a built-in reflector. This set is somewhat more expensive than a finished PL-L fitting, but you get a better depth effect.

For a maximum area of ​​50 × 80 cm you can use the 110W (2x55W) set. You get 275W / m 2 , which is in the optimal range.

As with LSR, you must use PL-L tubes with different color spectrum for growth and flowering. In doing so, the same rules apply as for LSR. Only the same color code can be used compare the luminance of two PL-L lamps.

Buy the following:

  • Growth phase : 860 (about 6000K) or 865 (about 6500K)
  • Flowering phase : 827 (about 2700K) or 830 (about 3000K)

CDM / HCI lamps

CDM stands for  ceramic discharge metal-halide and is the technology of Philips. HCI is the competition variant developed by OSRAM. Both are in principle a further development of MHL / HPS lamps. The concept is the same in both variants: The lamp is made of transparent alumina ceramics instead of quartz glass, as is the case with MHL / HPS.

CDM- HCI lamps
CDM- HCI lamps

The design of the CDM / HCI has many advantages. The lamps are  far more efficient in low and medium power ranges (up to 300W). The wider  color spectrum and the lower heat generation are also  a plus in the MHL / NDL models.

Please note
However, a CDM / HCI must always be operated with a protective glass, as in rare cases (and improper handling) the lamps can burst and the extremely hot glass can fly in all directions because of the high internal pressure. And  unfortunately, there are hardly any finished reflectors with protective glass which you can buy meaning DIY construction is often necessary.
If you are planning a change, you should read the CDM / HCI lamps and get a solid electrical knowledge  . And the changeover should be well thought-out, since the purchase costs for the ECG and reflector and protective glass can be quite high .

In the coming years, however, this could change as the market slowly establishes itself and the G12 socket on the CDM / HCI market. 
As with LSR, you must buy different CDM / HCI lamps for flowering and growth phases. Fortunately, the manufacturers use the same color codes. Due to the design and technology, the 9XX lamps offer better color spectrum than the 8XX. Also pay attention only to buy lamps with the G12 socket other sockets are not common.

Buy the following colors:

Growth phase: 942 or 865 (ca 4200K)
Flowering phase: 930 (about 3000K)


LED (stands for light emitting diodes) is probably the most exciting technology in indoor growing. Especially in recent years, the technology has made great strides. LED’s used to be used for hobby grows. There are now ready-made LED panels to buy, so that all growers can use LEDs in their grow rooms.

LED light emitting diodes
LED light emitting diodes

The biggest advantage is the really high efficiency of the LEDs, to which no other type of lamp approches. They generate far less heat than HPS / MHL lamps and therefore require less exhaust air output and can be placed closer to the plants. Add to that the very long life of the LED diodes. A further advantage is that no ballast is needed . In addition, LED panels are extremely easy to use and safe to use. The construction of LED panels is super fast (takes a few minutes) and you do not need any knowledge of electrical or wiring.

Growers with a small budget are deterred by the high purchase price. This is often many times higher than in HPS / MHL. The selection of a suitable LED panels is often difficult . Since there are many types of LED and manufacturers. 

LED panels are the universal lamps par excellence! Whether used in a high or low grow room, whether mini grow, scrog, SOG or cabinet grow – LEDs are suitable for all grow techniques!

The purchase price is high, but due to the long life and very low power consumption you save a lot of money over the years. Important is the selection of a high-quality LED panel with matching color spectrum for flowering and growth phase. Only if the components are of high quality, can you count on a long life and a fat harvest.

There are a lot of LED panels to buy on the internet. Growers should use a tried-and-tested model, because many unknown panels have product specification missing and often the components are inferior.


Now we come to the exciting question: Which lamps are the best for you as a new grower?:Buyer’s guide

The answer: It depends .

Which lamp is suitable for you depends on many factors:

  1. Is it your first grow or do you already have some experience?
  2. What is your budget?
  3. How many plants do you want to grow?
  4. What is your electricity consumption?
  5. How big is your growbox?
  6. How warm / cold is the environment of your growbox?
  7. How large is your extractor fan?

To make sure your head is not exploding, you will get a shopping list for a solid and proven setup.

Starter Setup

Start with a solid base that teaches you the art of indoor cultivation and gets a feel for the growing. So you get a guaranteed harvest and can still optimize your setup.


Many grow shop owners recommend new growers start directly with 400W or 600W lighting. I wouldn’t recommend this! Not only is the fun of your first grow unnecessarily more expensive – in 99% of cases it will be too hot in your Grow room and as a result your grow will suffer.

Trust me , with 150W you can get a great first harvest, even if others claim the opposite.

Recommendation to beginners:

  • Start with 150W MHL / HPS or 250wW HPS dual spectrum : These lamps are guaranteed to give you a fat harvest. Other lamp types and more powerful lamps are best used later when you have more experience.
  • HPS bulbs can be bought which are dual spectrum suitable for vegetative growth and also the flowering phase : So you do not have to buy a second bulb this is a great way to save money and is perfect for the first time grower.
  • Note that there is no 150W version of the dual spectrum bulb, since the deployment only makes sense from 250W
  • Grow box not too big : 0,3 – 1m2 are enough. If the grow box is too big, you will lose the luminosity of your lamp
  • Reflector: To use the full luminosity, always use the lamp with a reflector. 


Advanced setup for the experienced grower:

If you already have grow experience and want to grow more plants, it is time to upgrade your lighting. In order not to make it unnecessarily complicated , you can simply go to HPS and/or MHL in accordance with this table for performance and buy the right lamp (s) and ballasts buy.

MHL / HPS power in watts Area in m2 Number of plants
150 0.3-0.5 Max
250 0.5-1 Max
400 1 – 2 Max
600 2-4 Max

Table 1: Lamp power, area, no. Plants at Growbox with at least 160cm height

The values ​​are based on my experiences, all guidelines are approximate. Stick roughly to the values ​​of the table and you will have a solid grow.

For low-budget grows: 

Osram and Sylvania offer a special HPS with increased blue content, which is also suitable for the growth phase. Compared to the Nav-T for the growth phase, it also has a little more luminosity. So you need to buy only one lamp for both grow and flower phases.

Drawback : Experience have shown that with these lamps the plant has a slight tendency to stretch. The plant is no longer quite bushy. The distance between the internodes (distance between bud sites)  is slightly higher than in a pure Veg lamp.

If your grow box is not particularly tall, this can lead to problems. In addition, by stretching the lower leaves get a little less light. Note that there is no 150W version, since the deployment only makes sense from 250W.

Necessary accessories

Time switch (for all lamps)

Use the timer to set the light cycle. The light cycle is the time the light should be on and how long it is off. 18/6 for veg growth and 12/12 for flower

Dont forget!

Remember that you also have to take care of ventilation and odor control (activated carbon filter). Because MHL and HPS lighting always produce heat, you have to scale up your ventilation so that your plants do not become too hot.

I hope you found Best grow lights for indoor cannabis growing 101 useful,  good luck!



  1. A great read and some invaluable knowledge in a well thought out and written peice covering allot of stuff you have yo go digging for such as tips on sockets etc…. nice 1

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