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In nature, plants rely on the light spectrum that is produced by the sun. When growing cannabis indoors we try to emulate optimal outdoor conditions to the best of our ability. This means having similar CO2 and oxygen levels, temperature, humidity etc. and especially replicating the daylight cannabis plants need. Growers can choose between use 2 types of grow lights: regular lights and “High Intensity Discharge” or HID lights. Regular lights include standard lighting such as fluorescent or L.E.D. and do not require any additional devices to run. HID lights usually use bulbs filled with pressurized gas and and require ballasts to regulate the electrical current. Without a ballast, HID lights would burn out or even explode in seconds. The most common types of HID bulbs for growing cannabis are high pressure sodium (HPS) and metal halide (MH).

photo of the sun
The sun is the best grow light there is, this is what we’re trying to imitate.

There are several important issues to consider when choosing between different grow lights, the most important one being that your yield is highly dependant on the amount of lights your plants receive. The statement that “more grow light equals more yield” is true until a certain maximum, but it can be difficult to estimate this maximum. When choosing a light you should also consider how efficient your setup has to be and in what sense. Do you want to save money up front or in the long run? And will it physically fit in your grow space? Do you plan on using this grow light for vegetative growth or flowering? Or both?

Another issue with grow lights is that a part of the energy used is always wasted as heat. This can work both ways: purposely using hot HID lights in colder climates can help save on heating, while using anything hotter than LED lights can be difficult in warmer climates. If you live in a very cold area for example you use so much energy heating your grow room that less heat emission from your grow light wouldn’t necessarily be a good thing. In the rest of this article, we discuss the pros and cons of different grow lights and make recommendations.

H.I.D. Grow Lights

The Pros And Cons Of H.P.S. Grow Lights

HPS stands for High Pressure Sodium, this is a type of HID bulb that uses sodium and is considered the gold standard of grow lights. These bulbs generally come in 150w, 250w, 400w, 600w and 1000w versions and must be paired with a ballast that matches the wattage. HPS lights provide a full spectrum of light, but have an emphasis on the red end of this spectrum. They can be used for the entire life cycle of a cannabis plant, but many growers argue that the extra red light makes HPS lights optimal for the flowering phase.

hps grow lights
HPS grow lights are the industry standard. This grow uses a staggering 35 1000 watt HPS lights!

HPS lights are considered to be the ideal lights for growing cannabis for several reasons. They are relatively affordable and easy to use for the everyday grower, and perform very well. Despite several drawbacks, it is hard to beat the performance of HPS lights. Whenever new grow lights for indoor marijuana are developed, they are usually judged on how well they compare to HPS lights with a similar wattage.

double ended hps bulb
Double ended HPS bulb. HID bulbs come in regular and double-ended versions, make sure all your hardware matches your bulb!

The downside to using HPS grow lights is their efficiency, the main problem is usually the heat generated by both the ballast and the light. With temperatures exceeding 400°C, this system does not use energy very efficiently. The penetration of these lights also diminishes very rapidly and can drop by almost 90% at distance of only one metre. These inefficiencies have caused the European Union to ban the production of High Pressure Sodium grow lights and stimulate the transition to more environment-friendly alternatives like L.E.D. lights.

It is important to note that HID bulbs classically only connect at one side, but more modern grow lights use double-ended bulbs. These double-ended bulbs connect at both sides and are up to 30% more efficient than regular bulbs. Double-ended bulbs are simply better than single-ended bulbs, but this is also reflected in the price.

In short, HPS lights are definitely very good for growing cannabis. However, the amount of power consumed can become expensive and unfortunately much of this energy is wasted as heat and sound.

Metal Halide Is Similar In Use To HPS

The other big HID bulb is the Metal Halide or MH bulb. These bulbs also require a ballast and are similar in use to HPS bulbs. MH grow lights emit a full spectrum of light, but emit more blue light than HPS bulbs. Also available in 150w, 250w, 400w, 600w and 1000w versions, these bulbs are also commercially popular but not as popular as HPS. Metal halide lights are used for football stadiums and car parks, so are well known for the bright white light which is more similar to the sun than HPS lights. For cannabis cultivation MH grow lights are mainly used during the vegetative stage but they can also be used during flowering. They cover a much larger part of the light spectrum than HPS lights, which makes for healthier plants according to many growers. Their popularity for the vegetative phase is due to the larger amount of blue light they emit compared to HPS lights. Compared to the mostly red spectrum of HPS lights, this reduces the amount of stretching and makes for smaller, bushier plants. One drawback of these bulbs is that they cost more than HPS bulbs as the production process is more difficult.

Regular Metal Halide lights use quartz to ignite the lights but this can also be done with a ceramic arc tube. “Ceramic Metal Halide” (CMH), “Ceramic Discharge Metal” (CDM) and “Light Emitting Ceramic” (LEC) are all different names for this type of alternative MH bulb, we’ll refer to them as CMH in this article.  The term LEC started as a trademarked name by Sunsystem for a specific setup that uses 315W ceramic metal halide lights. The term is often used to describe systems that also use a different wattage than the classic options. CMH bulbs are similar to regular MH tubes in both use and function, but CMH bulbs are slightly more efficient and durable, they also produce a slightly better spectrum of light. The better light spectrum mostly revolves around UV-B radiation, which can improve resin production and terpene content.

hps vs mh bulb grow lights
HPS bulb on the left and MH bulb on the right. HPS and MH bulbs are often very similar, with the only difference being that MH bulbs are often wider.

It is good to know that you don’t have to decide between metal halide or high pressure sodium lights if you can afford two bulbs. Ballasts that run MH lights are able to run HPS lights and vice versa, as long as you use the right wattage. A common way to use this to your advantage is by using a MH bulb during the vegetative phase and switching to a HPS bulb during flowering. If you want the best of both worlds, there are also many different types of combination bulbs. These use a dual arc system and are essentially a HPS and MH light in one bulb.

Non-HID Grow Lights

L.E.D. Lights: The Future?

LED grow lights seem to be the answer to all the problems HID lights have and are taking over the industry slowly but surely. LED lights are brilliant in terms of energy consumption, heat energy and light energy, they also do not require any ballast whatsoever. The fact that they produce much less heat also makes them virtually invisible for heat detection cameras, making them a bit more stealthy than HID lights. The main attraction however is their efficiency in terms of power consumption. Most grow lights emit many different wavelengths of light (radiation) and are not specifically tailored to a plant’s needs. LED grow lights are much more specific, and emit much more “PAR” light, or photosynthetically active radiation, per watt of energy used.

example of infrared scanner
Infrared cameras can make your subtle little grow light up like a christmas tree! Problems with heat are much easier to keep under control using LED grow lights.

The industry is still developing itself rapidly and there is no clear gold standard, this causes LED grow lights to be very different between companies. Features that are often different include the type of diode, the angle of the lens and which wavelengths are used. This in turn causes differences in PAR levels, light penetration and the color of the light. With so many different types to choose from and the drastic differences in heat and power draw compared to HID grow lights, LED lights are a pleasure to grow with.

led grow light with coloured diodes on the left and a full spectrum grow light on the right.
LED grow light with coloured diodes on the left and a full spectrum grow light on the right. There is even a big discussion within the LED light scene about which colours should be used. The fact that different companies are producing such vastly different products is a clear sign that research in this area is not nearly done!

The only downside to these lights can be the overwhelming cost to invest, which can seem daunting to a grower who has only ever spent a few hundred euros on their lighting. The best LED grow lights can cost up to ten times that amount! They are however, well worth it and can make this money back in the long run through your electricity bill. The current top LED grow lights are able to give you over twice the yield of HID lights in terms of gram per watt of energy used.

Light Emitting Plasma (LEP) Grow Lights: The Forgotten Grow Lights?

Light Emitting Plasma are being used more and more in commercial agriculture recently, but the technology goes back to Nikola Tesla in the 1800s. LEP lights have many of the advantages of HID lights, but don’t have moving parts, emit unidirectional light and provide a record number of lumens per watt. With the center of an LEP light burning at 6000K, which is similar to the surface temperature of the sun, these lights produce a spectrum that looks very close to natural sunlight.

There are however many reasons why LEP technology is not as popular as HID or LED lights. While the spectrum is more similar to natural sunlight than HPS lights for instance, this does not mean that plants actually use all this light. LEP lights emit a lot of yellow and green light, which are both barely used by flowering plants. LEP lights generally don’t provide enough red light for a flowering cannabis plant, but are often added in HPS grows to increase bud quality. The large amount of blue light they emit also makes them very suitable for the veg phase. The main problem is the price: most growers simply aren’t willing to pay 1000+ euros for a supplemental light.

Because they are rarely used as a stand-alone light it is unclear what yields to expect from LEP grow lights. They definitely have a place in the grow room though and will improve the quality of your yield, but will probably not have much effect on the quantity. At the moment LEP lights are still too expensive for the average home grower in our opinion.

Fluorescent Grow Lights: CFL, T5 Strips, etc.

Fluorescent lights are used all around the house and can be bought at local stores very cheaply. These come in many different shapes and colours and most of them can be used for growing cannabis. Old-school fluorescent bulbs were always the same bar-shape, but CFLs, short for compact fluorescent lights, come in many different shapes. The colour is indicated with a Kelvin rating, or K value. Common household lighting colours include 3000K for “warm white” and 4000K for “normal white”. There are also specific fluorescent grow lights, these come in two spectrums: blue light (6400K) and warm red light (2800K). While you can use regular fluorescent lights for growing cannabis, fluorescent grow lights will perform much better.

best kelvin colour code for growing cannabis
Fluorescent lights are available in all shapes, sizes and colours. Make sure you get the right ones for your specific needs.

The best fluorescent grow lights are probably T5 lights, which are used in veg rooms to keep plants under a cover of soft white light. Growers will combine a number of T5 grow lights together and create a ceiling of white light or mix colours to better fit their specific grow.

Fluorescent grow lights have a low power consumption and give out hardly any heat, so they are brilliant to keep very close to the tops of the plants. In the vegetative stage these lights are great for seedlings and rooting clones. The only negative about using fluorescent grow lights is that they usually produce less light intensity than other bulbs, so the final density of the buds will be noticeably less even though the actual buds have finished well. Fluorescent grow lights are great for growing cannabis in small spaces, and are always a solid choice for the vegetative phase.

fluorescent grow lights for vegetative growth
Fluorescent grow lights are mostly used during the vegetative phase.

The downside of fluorescent lighting is that they are much less effective for the flowering phase. Fluorescent grow lights usually only yield around 0,25 gram per watt, whereas HID lights usually reach four times as much. Once scaled up to a similar light output as a HID grow light, the power draw, heat production and investment also increases. A fluorescent grow light setup that provides enough light for multiple large cannabis plants will still draw a lot of power, produce a lot of heat and cost a substantial amount of money. A 125W fluorescent bulb might not need a ballast, but will cost about three times as much as a 150W MH bulb.

In general though, fluorescent grow lights are great to use on a smaller scale. This way they can be very efficient on power usage and a provide an easy, cheap solution to vegging seedlings or clones. All in all, fluorescent grow lights are second only to LED in efficiency (during veg) and user-friendliness.

Get A Grow Light For Flowering

Make sure to read our guide on how to use different types of grow lights as well for a more thorough discussion of which grow lights to use in which situation.

little plant does not need 1000 watts
This cute little plant does not need 1000 watts of energy yet, but they grow up so fast! Remember that flowering has to last two months or more, so make it your priority!

It Comes Down To HPS versus LED

And while fluorescent and MH lights do have their niches, HPS lights are definitely the standard. The position of LED grow lights is more debatable, as these are still developing rapidly. The more affordable LED lights are often not strong enough to produce high yields, while the ones that can usually cost an arm and a leg. For this reason the real choice you have to make is between HPS and LED. Think about it: most LED companies advertise their lights with lines like “equal to 600W HPS”. HPS grow lights are tried and true, with no unknowns in the equation: you know it’ll cost a lot of money and get hot, but you know it’ll work.

LED grow lights are the latest technology that promises to solve all of the problems the current technology has. Good LED grow lights produce buds that are as good as those grown under HPS light, but don’t get too hot, don’t make noise and save lots of money on electricity.

led and hps grow
Don’t worry if you can’t decide, even commercial growers still haven’t either. This picture is from a commercial grow in California where half of the plants were grown under LED and half under HPS. Even on this scale, where everything makes a huge difference, the HPS and LED lights performed similarly.

So if you are currently in the market for a new grow light, you have to ask yourself several questions. How well can you manage the heat of a HPS light and ballast? How much money are you willing to spend on your light? And how much on electricity? Finally, how much faith do you have in new technology? We wish you the best of luck choosing your new grow light and of course happy growing!

After deciding on which lights to get, you need the plants to match:

best yielding strain