Growing Cannabis With High Intensity Discharge (HID) Lights

One of the most important aspects of setting up an indoor grow is undoubtedly the lighting. Beginners may be overwhelmed by the options and we don't blame you. Although it can be confusing to know where to start, we have a number of solutions that can ensure our cannabis plants are getting the correct amount of light. This article discusses HIDs and how to use them for growing top quality indoor cannabis.

Growing Indoor Cannabis

HID (High Intensity Discharge) lamps dominated the market for years and continue to get better in terms of their efficiency. HIDs have allowed growers to maximise the potential of their indoor operation and provide the type of light cannabis plants need to deliver top harvests.

The rise of LED technology has lead many growers to make the switch from HIDs. However, high quality LED lights can be well out of the average home grower's budget and are extremely expensive to install in large scale operations, so HIDs remain a popular choice among many.

There are many types of grow light you might hear about, including CFLs (compact fluorescent lights), T5, LED (light emitting diode), CMH (ceramic metal halide), LEC, and others. 

It is true that LEDs have definitely caught up and very often they are as good, if not sometimes better than HIDs. Saying that, HIDs are still the go to light for plenty of professional growers, who use them with great success.

What is an HID (High Intensity Discharge) Lamp?

High intensity discharge lamps are bulbs that produce light by passing electrical current through two electrodes contained within a high pressured arc tube. When electricity passes through a ballast connected to the bulb, gasses in the arc tube begin to excite and heat up. As this happens, metallic salts within the arc start to vaporize, and an intense light is produced.

HIDs can be found in all sorts of places, including car lights, street lamps and stadiums. Since they we're discovered to be ideal for growing cannabis, the design of HID fixtures has evolved and improved to make them more user-friendly and accessible to those looking to safely set up a grow room.

For cannabis, we can use two different HID bulbs throughout the grow cycle, one metal halide (MH) for vegetation and one high pressure sodium (HPS) for flowering. The bulbs need a reflector which has as wider spread as possible. The reflector is suspended from the top of the grow space or tent using adjustable pulls/rollers for easy positioning.

Pros and Cons of HIDs

The biggest downfall of HID lighting compared to the modern alternatives is their power consumption. LEDs and CFLs are generally better for those looking to save on electricity costs in the long run but many would argue HIDs still give the best results.

To give a fair argument, let's take a look at some of the pros and cons of HIDs.

Pros of HIDs:

• Cheap compared to other types of grow light such as LEDs
• Fast plant growth
• Deliver large yields when used correctly
• Reliable technology that has been around for years
• Suitable for all scales of grow
• Measured in actual watts, not an equivalent, like many CFLs or LEDs products.

Cons of HIDs:

• Efficiency decreases over time
• Consume a lot of electricity
• Require their own space
• Produce excessive amounts of heat
• Involves the use of extra equipment such as ballasts
• Produce a lot of light pollution.

Choosing The Right Light For Your Space

If you're unsure about how much light you need in your grow room, consider the size of the space you're working with. In general, around 400-600W of high intensity discharge lighting per square meter is enough to grow high yielding cannabis plants. With this is mind, not all stages of growth require the same light and most growers will switch their bulbs once or twice during the whole cycle.

Adding excessive amounts of light does not necessarily mean plants will produce more bud. Just like the sun can be too strong for us, powerful indoor HIDs can burn cannabis plants, especially as the light source is generally in close proximity to the tops of the plants. Most growers start with weaker lights (like CFLs) when the plants are still seedlings and as they become accustomed to the environment, introduce a metal halide or full spectrum HPS.

How close you are able to place the lights to your plants without burning them depends on the output of the bulb but it helps to start with around 60-75cm of distance and move them closer as the plants grow up or if you notice them stretching too much. The more powerful the bulb, the hotter it will run, and therefore cannot be placed as close as a bulb that has a low output.

As you progress through the grow, the lights can be gradually placed closer to the canopy, being sure to keep a safe distance:

Small scale grow operations may be better suited to less powerful HIDs, which come available in 150-250W sizes.

Tip: Place your hand palm down underneath the light after it is fully on and feel how close you can get your hand to the bulb before it starts to get uncomfortably hot. You can use this to gauge whether the light is too close to your plants.

Different Types of HID Light For Cannabis

This section gets into details about the two most commonly used HID lights; metal halide and high pressure sodium bulbs.

MH (Metal Halide)

Metal halides emit a white, blueish light, making them ideal for vegetation. A metal halide has a kelvin rating of around 6500k which means the light has a blue tint. Depending on their output, they can produce between 60-110 lumens per watt. They can be used for whole grow, but most growers switch to an HPS for flowering. 

Zkittlez 2020 Autopot Canna Nutrients

Metal halide lamps we're used a lot more back in the day before LEDs and CFLs proved themselves to be more energy efficient alternatives for vegetative growth. Metal halides have regained popularity since the release of the CMH (ceramic metal halide), often referred to as LEC. These produce more lumens per watt than regular metal halides and have a longer life span.

HPS (High Pressure Sodium)

HPS bulbs are used mostly for flowering because they emit less blue or white light and instead give off more light within the red/yellow part of the spectrum (a lower kelvin rating between 2500-3400K). However, there are now HPS bulbs labelled as 'full spectrum', which include a wider band of colour wavelengths, making them suitable for the entire grow cycle.

A high quality high pressure sodium tends to win in terms of lumen output, delivering around 90-150 lumens per watt of power. They also have a longer life span than metal halides, lasting up to 6500 hours.

Ballasts

Ballasts are electrical current converters that cause an HID bulb to ignite. The ballast controls the flow of electricity and slows the current down. Without the ballast, it would simply be too much for the bulb to handle and the current would continue to increase in the bulb, causing it to overheat and explode.

There are two main different types of ballast that are commonly used for connecting HID lights.

Magnetic Ballasts - These are more the old fashioned type of ballast used mainly before the invention of digital ballasts. Magnetic ballasts are an affordable option but produce large amounts of heat due to the way they work.

Magnetic ballasts regulate the voltage using an induction coil through which the electrical current passes. Capacitors reduce the voltage and keep it at a steady level to provide power to the bulb. The power of the ballast is determined by the size of the coil.

Digital Ballasts - Electronic or digital ballasts can get pricey compared to magnetic ballasts but are worth the investment for those looking keep heat and energy costs down. The multiple coils in a digital ballast means they do not need to produce as much heat to maintain the current running through the bulb, and therefore less energy is wasted.

Digital ballasts can also regulate the frequency of the current without changing its voltage. This allows them to run much quieter as the flow of electricity becomes more constant. Another advantage of electronic ballasts is they can have multiple bulbs connected to them, either in parallel or series. This means they can be set up so that if one light fails, the other lights remain unaffected.

Digital ballasts are generally smaller and more lightweight than magnetic ballasts. They are easy to set up, and do not require much maintenance. 

Tip: When purchasing a ballast, make sure it is compatible with the power of the light you intend to use. Hang it in a place that has plenty of airflow and clean dust away frequently. 

Understanding Lumens, PAR and PPFD

Without getting too technical, we wanted to discuss the relevance of terms such as lumens, PAR and PPFD. You may come across these metrics while researching for grow lights  and be wondering what they mean for your cannabis plants.

Lumens is simply a metric humans have created to measure the intensity of a light. Also referred to as luminous flux, lumens describes the amount of energy being produced within the range of wavelengths we are able to perceive.

When we think about the electromagnetic spectrum, humans are able to see between wavelengths of around 380 - 680 nanometres (nm). Cannabis plants respond to wavelengths between 200 - 800nm. However, it has been seen that photosynthesis is most active when the plant is exposed to ranges between 400 - 700nm. This band of light spectra is known as photosynthetic active radiation, or PAR.

Measuring lumens can tell us the output and efficiency of a light in relation to the wattage but it doesn't give us any information about the spectrum or PAR output. Generally though, the more lumens per watt, the better. Higher lumen output per watt can also mean a broader spectrum of light or closer to white.

But what is PPFD? PAR is mostly used as a photometric measurement in LED grow light technology, whereas HIDs tend to only offer lumen output information. PPFD, or photosynthetic photon flux density, is a light metric used commonly in the indoor lighting industry to measure how many PAR light micromoles are distributed every second within a metre squared (μmol/m²/s).

If the PPFD output information is provided, light efficiency can then be calculated against the wattage. To give you a brief idea of how cannabis plants respond to PPFD, we can again take a look at the sun's energy. Depending on where you live, the outdoor summer sun can provide up to 2000μmol/m²/s. However, cannabis plants do not need such a heavy dose until they are in flowering. See the following chart:

This gives us an idea of the density of the photons reaching our plants and within what spectrum they fall. Do not worry too much about PPFD if you are just starting out, as most high quality grow lights are designed to produce light that cannabis plants thrive on. Keep in mind that choosing grow lights from reputable brands is always best, and try to find out as much information about the light and ballast as you can.

Installing HID Lights

Whether you use a grow tent or have a custom built space, securely fixing the lights is very important. You never want the light fixture to collapse as this could be the end of your grow, or worse. HID lights can be a massive fire hazard, so ensure the structure you're attaching them to is stable and can support the weight along with fans, extractors and carbon filter.

Most reflectors come with loop holes to attach the lights to a hanging system. This system should allow you to easily raise and lower the lights as needed. There are automated systems for this part of indoor lighting, but with some simple roller hangers found in most grow shops you can setup and manage the light height with ease.

Using HIDs For Different Stages Of Growth

As we briefly mentioned earlier, each stage of growth for a cannabis plant benefits from certain light adjustments. When we look at how light changes outside, we can understand how our indoor plants respond to the light we provide them.

In spring, the light that passes through the ozone contains plenty of blueish light. Young cannabis plants in vegetation need blue light in order to grow foliage and to develop into big, strong plants before it's time to bloom. 

More red light seeps through the atmosphere at the end of summer, signalling many plants that it is time to fruit or reproduce. As the days get shorter, the cannabis plant produces flowers (buds) as a way to mate or produce seeds before it dies in the winter.

Mimicking these conditions indoors is what has allowed growers to shorten the vegetative cycle and immediately start the flowering process as and when they choose. After a cannabis plant has spent 18 hours daily under blue/white light throughout its vegetative cycle, a grower will switch the light schedule to 12 hours of daylight to force the plant to flower. At this time, more red spectrum light is necessary for the plant to produce big, healthy flowers.

Tips and Tricks for Growing With HIDs

So this post doesn't drag on for too long, let's end quickly with some tips and tricks to help you manage HID lights in the grow room.

• Connect the ballasts to timers so your light schedule can be set up automatically.
• Replace the bulbs after about 12 months of daily use (12h per day).
• Clean the reflectors and bulbs between grows to remove dust.
• Set up a proper ventilation system to expel the heat produced by the lights.
• If you want to get really accurate with the light, consider purchasing a light meter.
• Ask the manufacturer for all the information about the light.

HID grow by Regenwurm (Northern Lights #5 x Haze - Sensi Seeds) from GrowDiaries.

Conclusion

Growing with HIDs is a reliable way of keeping your cannabis plants well fed with light. Try not to get too overwhelmed by all the different metrics in the beginning and just aim for the highest quality lights within your budget. Remember, it is not all about the highest output light, but the space you're growing in and stage of growth you are focusing on. We hope this article helped somewhat.

If you found this post useful, feel free to share your thoughts about HIDs down in the comments section!

External References

Closing the Yield Gap for Cannabis: A Meta-Analysis of Factors Determining Cannabis Yield. - Backer, R., Schwinghamer, T., Rosenbaum, P., McCarty, V., Eichhorn Bilodeau, S., Lyu, D., Ahmed, M. B., Robinson, G., Lefsrud, M., Wilkins, O., & Smith, D. L. (2019).

Luminous Flux Variation on High-Pressure Sodium Lamps. - Espín, Francisco & Muñoz Ramos, Cindy & Araguillin, Ricardo & Chasi, C. & Velásquez, Carlos. (2016).

Photometry and Photosynthesis: From Photometry to PPFD (Revised). Wordpress Blog. - Ashdown, Ian. (2015).

Comparison Of Different Light Sources At Equal PPFD. Acta Horticulturae. - Meyer, J. & Horn, W.. (1995).

High-pressure Sodium Lamps Electronic Ballasts. - André, Anderson & Perin, Arnaldo. (2003). 

Mercury and Metal Halide Lamps. - Dobrusskin, Alexander & Heider, Jürgen. (2020).

Energy Consumption Model for Indoor Cannabis Cultivation Facility. - Mehboob, Nafeesa & Farag, Hany & Sawas, Abdullah. (2020).

This article was updated January 2021.