What to consider when choosing Cannabis Grow Lights

Posted on Jan 06 , 2021

Light is a critical element in the life of cannabis. Not only the efficiency and generosity of the harvest, but also the life of the plant in principle, will directly depend on its quality and quantity. Therefore, the grower must be extremely careful when choosing the right lighting for cannabis.

  • What parameters to consider when choosing a grow light for cannabis?

  • Induction grow lights and CMH

  • HPS, LED or ESL?

  • How to calculate the grow light wattage depending on the area of the grow box?

With outdoor, everything is clear - there is only one “light bulb” and it is called the Sun. It is enough just to competently approach the choice of a place for a plot. But when it comes to indoor, then several options open up before the grower, among which you can get lost. Globally, suitable grow lights can be divided into 3 types: HPS, LED and ESL. Each type has advantages and disadvantages, as well as a bunch of specific device types. This article will help you make the right choice and correctly place the grow light in the box.

1.What parameters to consider when choosing a cannabis grow light?

Older growers will most likely give the following advice: "Just take a 400-600 W HPS grow light , you can't go wrong." Partly they will be right, partly wrong. For a long time, growers have focused on energy consumption as a factor in luminaire efficiency. Then they started comparing suites and lumens, which is also not entirely true. Now we will give you a quick reference on all the main units of measurement, tell you what they mean and what to look at in the end.

Watts (W) - This indicator reflects the amount of energy consumed by the luminaire. But to consume does not mean to give. For example, let's take a 400 W HPS grow light. This figure indicates that it consumes 400 watts, but how much of this energy is converted into useful light, given that its operating temperature can exceed 600 degrees? The average efficiency of a sodium grow light is only about 30%. For this reason, a 180 W LED grow light can easily surpass HPS in energy efficiency.


Lumen (Lm) is a measure of the amount of light emitted from a grow light and is closely related to lux, a value about which below. Lumen refers to how much light a source can produce in principle. But the amount of light is not at all equal to its quality. What difference does it make how brightly the conventional Ilyich's grow light burns if there is not even a hint of a useful spectrum in it, and the plants die?


Lux (Lx) - this parameter shows how much light falls on one square meter. Again, not the most basic indicator for a gardener, because it does not give an understanding of what kind of light we are talking about.


PAR - but this is closer to the truth. In general, the abbreviation PAR stands for photosynthetically active radiation and is not a measure like a watt, kilogram or the same lumen. PAR is basically a wavelength range of 400 to 700 Nm.


PPF - and this is exactly what you should pay close attention to. This metric reflects the number of photons from the PAR region that fall per square meter of foliage every second. PPF is measured in umol / m² * s (micromole per second per square meter).

On a sunny day outdoors, the PPF is about 2000 mmoles per square. Some grow lights provide even greater efficiency. But in general, a cannabis bush with a margin will be enough for an indicator of 500 μmol per square meter per second.

Please note that this parameter depends not only on the power of the grow light, but also on its distance from the plant. The main thing is to provide such a distance that as many photons as possible fall on the bush. We will discuss this below.


PPFD is the amount of light photons that hit a surface (your plant canopy) in one second. It’s measured in units called micromoles (μmols). Simply speaking – it’s the strength of the light that reaches your plants.

The light loses strength as it travels from source to endpoint (from grow light to plant). You’ll notice on most grow light intensity charts, the PPFD numbers decrease with increased distance from the light.


2.Induction grow lights and CMH


We will only mention induction grow lights for cannabis and CMH in this article, without going into details. No, plants thrive under these light sources, but their price (at least what is currently available) makes these grow lights only suitable for large farms. They are too expensive for the average grower, and given the size of an average cannabis grow box (an average of 2 to 5 bushes), the costs would be completely unjustified.

Induction / plasma grow lights.

For the first time the technology used in these grow lights was invented back in the 19th century by the notorious Nikola Tesla. The main difference between induction grow lights and all others is the absence of electrodes. The glow is provided by an electromagnetic field inside the bulb. Due to this, induction grow lights last many times longer than any others. In fact, this is where their advantages end.

Picture. Induction Plant Grow Light


This is the “swan song” of HPS technology. These grow lights have a double burner and a light spectrum that is as close as possible to the sun. Even the glare coming out of the growbox will look more like "sunbeams" rather than traditional light from grow lights. If we compare this technology with conventional sodium grow lights, then it will be better in everything by about 30-40%. They heat less, have a more “correct” and efficient spectrum, and can be controlled remotely from anywhere in the world using a smartphone application. The kit, as in the case of HPS, consists of a grow light, the grow light itself and ballast. It is worth saying that a sodium grow light choke will not work, so you should not use it. For the price of one such set, you can get a pretty good ready-made grow box with all the necessary equipment.


Picture. CMH Plant Grow Light

3.HPS, LED or ESL?

These 3 types of grow lights are the most popular choice for growers. Let's look at their advantages and disadvantages, and at the same time find out at what distance it is better to place them from the plant.



A technology that has been in use for over 60 years. Kind of like the gold standard for growing. It has the following main advantages:

  • The light spectrum of HPS grow lights also falls within the photosynthetically effective range. Simply put - under such a grow light the bush will grow in any case.

  • Excellent flux penetration, ensuring that photons reach even the lowest foliage.

The disadvantages include:

  • High energy consumption and low (about 30%) efficiency

  • The need to purchase and connect electronic ballasts / electronic ballasts (another name - ballast, or choke)

  • The need to install an additional ventilation circuit and difficulty with humidity / temperature

  • Fire hazard



This option, according to many growers, is the future. Today, LEDs are confidently pushing their sodium counterparts, having the following advantages:

  • Low power consumption and high (up to 80% and more) efficiency

  • No moisture and temperature problems due to almost no heating

  • Fire safety

  • No need to install an additional ventilation circuit and additional equipment

But you can't do without drawbacks:

  • Much less penetrating power of light than that of DNaT - ideally, additional illumination of the lower branches, the use of cannabis defoliation or LST is required

  • Good LEDs are expensive (but not so badly)

LED lights can be:

  • bicolor (two spectra - blue and red)

  • multicolor (more than 2 spectra)

  • full spectrum (even white or pink light, consisting of all 7 colors)

We recommend the third option, in the extreme case the second, since bicolor grow lights are suitable only for sublight or vegetation, during the cannabis flowering period it is better to give the cannabis all the maximum possible.


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This option, as it was a half measure, remained with it, which, however, does not negate some of the effectiveness of this technology. The main advantages include:

  • Cheapness

  • Low power consumption

  • Fire safety and no need for chokes and additional fans

  • Some effective spectrum with an efficiency of about 15-20%

Cons - everything else. This option is only applicable for very small growing volumes. It is advisable to raise no more than one bush under the ESL. But such grow lights are great for budget supplementary lighting. If you decide to spend the whole grow under the energy saving, then you will need 2 grow lights with different color temperatures:

  • 6500K - for vegetation

  • 2700K - for flowering.

Be careful not to break them, as there is mercury in the composition.

4.How to calculate grow light wattage depending on the area of the growbox?

Don't worry, you won't have to count - we have already done it for you and made a specific plate. In general, in this case, it will be more correct to focus on lumens and suites, because we need to understand the illuminated area, but, alas, not all manufacturers indicate these characteristics. But everyone points out Watts, which, however, also give a completely accurate picture.

So far, ideal lighting is considered to be the one with which the grower managed to get 1 g of buds for every 1 W of grow light power. Today some growers manage to surpass this figure using the latest developments in the field of lighting. This is a kind of standard of excellence that every gardener should strive for. This article has given you all the information you need to get started in this direction. All that remains is practice!

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