HID Lighting To Grow Indoor Cannabis Plants — A Complete Guide 

Cannabis growers have a lot of options to choose the best grow lights. Truth be told, the market has so many options that it can be confusing to choose among a vast array of lights.

But grow lights are one of the most important factors necessary to grow great buds, so you need to research and make good decisions because you cannot change grow lights often.

When it comes to grow lights, two of the most popular options are LED and HID lights. LEDs are becoming popular now but HIDs ruled the industry for quite a while and rightly so. Some of the most experienced growers use HID lights even today.

If you are a new grower looking to buy new grow lights or just want to elevate your growing journey to the next level with the best grow lights, you've come to the right place. You probably have a lot of questions about the price, size, wattage, and, most importantly, the yields the lights can produce.

We have covered a lot about LEDs in other articles but today we will discuss HID lights and how you can grow amazing cannabis plants and yield much more than you imagined.

What are High-Intensity Discharge or HID lights?

HID or High-Intensity Discharge lights, including lamps, produce light by sending electrical discharge between electrodes. These arc lamps do so using plasma or gas. Typically, additional gas is also used, which serves to distinguish between HID lights such as metal halides, sodium, and mercury lights.

Essentially HID lights work by sending electric arcs between electrodes made of tungsten present in an arc tube made of quartz. The quartz contains a mixture of metal salts and gas.

When there's an initial spark of electricity, it creates an arc that in turn heats the metal salts, thereby creating a plasma. In other words, the arc converts electricity to visible light rather than heat like halogen or incandescent bulbs.

Apart from being highly efficient, HID lights also have a long life. Typically, they need ballasts that create the initial electricity surge necessary to regulate power.

HID lights are typically used wherever there's a need for bright lights, such as in stadiums, gymnasiums, indoor grow rooms, etc, as they are popular to be highly efficient at converting electricity to light.

Gas discharge lights have existed for about 300 years. The same principles that were used long ago have spurred innovations in neon and fluorescent lights. Originally, the lights contained air; however, they were replaced with gases like xenon, neon, krypton, and argon after discovering that the gases could increase light output.

Modern HID lights have improved in technology by experimenting with gas mixtures. Even the electrodes are better although the basic principle hasn't changed.

One advantage of using HID lights is that they are inexpensive compared to LEDs. Although they may not be as efficient as LEDs in terms of power, a good portion of cannabis growers uses them.

The two most popular HID grow lights used mainly for growing cannabis are Metal Halides (MH) and High-Pressure Sodium (HPS) lights. One can use both lights for a full cycle of growing cannabis from start to finish. Many growers use both lights where metal halides are used at the beginning, or the vegetative stage and HPS lights are used during the flowering stage. This is done to maximize the light output and take advantage of both lights to get explosive growth and humongous yields.

What are Metal Halides?

As mentioned already, metal halides also work by passing electric arcs through gas mixtures. They are extremely powerful and work as great substitutes for natural sunlight. The mixture of the gases the light contains will determine the light it produces. Therefore you can find different metal halides that vary in intensity, color, and temperature.

Specifically, metal halides imitate light produced by nature in the autumn and spring seasons. They veer towards the blue light in the visible spectrum and since cannabis plants enjoy blue light during the vegetative or growing phase, growers use metal halides right from seedlings until the plants can be switched to the blooming phase.

The vegetative phase is the phase where the plant develops branches, stems, and leaves. The plant requires bright light for the process of photosynthesis and produces as many leaves as possible. Metal halides are perfect for this phase as they produce extremely bright light. 

On average, you can expect metal highlights to last for at least 10000 hours, translating to roughly 350 to 400 days. Since most growers let their plants grow for about 8 weeks in the vegetative phase, you can expect the lights to last up to 7 cycles, assuming the grower will use HPS lights during the flowering stage.

Compared to LEDs, metal halides are cheap and don't require a huge investment initially. Of course, the prices will vary as the power levels go up. You can replace the bulbs as soon as they die, thanks to their low cost.

What are High-Pressure Sodium lights?

High-pressure sodium or HPS lights are very similar to metal halides, except for the gas mixture. Unlike MH lights, HPS lights contain sodium that produces an orange or red light. Since cannabis prefers orange or red lights during the flowering stage most growers love using HPS lights to give the plant everything it needs to grow healthy and produce hefty buds. HPS lights are known to activate plant hormones and boost yields.

You can use HPS lights only during the flowering stage or combine both MH and HPS lights from the start of the cycle to create a good combination of both blue and red spectrums of light. However, your plants will love it if you can increase the red spectrum during the flowering stage, so it makes sense to use the MH lights during the vegetative and the HPS during the blooming stages.

HPS lights last longer than metal halides and can run up to at least 18000 hours or 700 to 750 days. But one disadvantage is that they consume more power compared to metal halides. As a result, they also produce more heat so you will need to take extensive measures to create more ventilation in your grow room. Some growers prefer to use air conditioners especially when they use HPS lights to control the heat. However, it can add to your budget, making your project an expensive venture.

What HPS watt size is best?

Generally, the watt size depends on many factors, including the space you have, plants, strains, and your experience. If your grow area is small, you can do well with the 400-watt bulb. If your growing space exceeds 4x6 feet you can go for 1000w but be very careful to provide a lot of vertical space for the plants to grow. HPS bulbs exceeding 1000 watts produce excessive heat and are mainly reserved for commercial grows.

If you're confused about the wattage, the best thing would be to purchase two 400w or 600w models, depending on your grow area. By purchasing two lights and spacing them out, you will also prevent hotspots and ensure that the canopy gets uniform light. Two 600-watt models will work perfectly to grow at least 10 to 15 small plants or 8-9 big plants.

Also, note that the lumens drop considerably when you place the lights farther away from the plants. The result is that you get less light covering more area.

You can calculate the intensity by dividing the output of the light by the distance squared. For example, a 400w light producing 100,000 lumens hanging above 4 inches will offer only 50,000 at 8 inches. The lumens will further decrease as you hang the lights far away. However, it's imperative to hang the lights at a distance as mentioned by the manufacturer or you risk a light burn.

How high should you hang HID lights?

Just do as the manufacturer says. It depends on the wattage.

However, here’s a simple chart:

What yields can you expect from HID lights?

No matter what light you use, the yield depends on the strain you grow. You can use 1000-watt HPS lights but it won't yield much if the strain is not meant to grow massively. In addition, the yield will depend on the quality of your light, ventilation, humidity, temperature, the nutrients you provide, etc. Typically most HPS lights are advertised to provide one gram, but it also depends on your experience and is tough to achieve.

It is not advised to use only MH lights for the entire growing period. Similarly, using HPS lights for your plants during the vegetative stage is not recommended as it does not contain UVB light that most MH lights produce. Using MH lights during the vegetative stage will result in stronger plants with stronger roots and bushier large leaves. Assuming that you use a combination of both HPS and MH lights, here's an estimation of the yields you can expect.

Cost of HID systems

It's a well-known fact that HID lights are cheaper when compared to LEDs; however, LEDs will prove to be cheaper in the long run mainly because HIDs have a lesser lifespan, consume more power, and produce excess heat that makes you install more fans and an air conditioner as well. Regardless, make sure you purchase your HID systems from reputable sources so that it works and lasts for at least 18000 hours. Here's an approximate list of prices of HID systems you can find on the market today.

Note that these HID systems are usually a combination of both MH and HPS lights. Also, the prices can vary depending on the ballasts you choose. For example, if the ballasts are digital then the prices will be higher. 

Since you need to replicate the solar rays found outdoors, you will need to invest in high-efficiency HID systems. The brighter the light, the more nutrients the plants absorb, thereby resulting in denser buds. 

However, don't go overboard and provide too much light as it can produce excessive heat and be detrimental to your plants. Always take a look at the growing area mentioned by the manufacturer before purchasing the light.

Electricity costs to run HID lights

So what will be my electricity bill if I use HPS lights — this is a question most growers ask. Although it depends on where you reside, it is possible to arrive at an approximate conclusion with a few calculations.

First, you need to find out the average price of the electricity where you live. For example, most locations in the USA charge 12-16 cents on average. Let’s imagine that you’re paying $0.15/kWh or kilowatt-hour. 

Now, you’ll have to calculate the number of hours the lights run. Of course, if you’re using two lights, simply double the number you get at the end. 

So, let’s assume that you let your plants grow for about 8 weeks during the vegetative phase. Most growers let the lights run for 18 hours per day. If you’re using it for 24 hours (which is not recommended) you’ll have to adjust the calculations. 

So, assuming you’re paying $0.15/kWh for 18 hours/day for 8 weeks, the calculation will be:

Total KW x kilowatt-hour X number of hours per day. 

To calculate the monthly bill, simply multiply (Total KW x kilowatt-hour X number of hours per day) x 30. 

Total Kilowatts are calculated by dividing the wattage by 1000. So, if you’re using a 1000-watt bulb, it’s 1000/1000 = 1 kilowatt hour or kWh

Your local electricity cost (assuming $0.15 in this case)

Number of hours = 18 hours during the vegetative stage (adjust it to 12 during the flowering stage)

Monthly rate = Multiply by 30

Thus, it’s Total KW x kilowatt hour x number of hours per day = 1 x 0.15 x 18 = 2.7 X 30 = $81 per month

If you want to calculate the cost for an entire cycle, here’s how you do it:

8 weeks @ 18 hours per day for the vegetative phase = 1008 hours

8 weeks @ 12 hours per day for the flowering phase = 672 hours

Total number of hours = 1008 + 672 = 1680 hours @ $0.15/kWh = 1680 x 0.15 = $252 per cycle.

Should I switch from HPS to LEDs?

Many growers who have used HPS lights in the past have asked this very same question — Should I switch from HPS to LEDs?

In the past few years, LEDs have firmly established themselves in the market, urging many people to wonder if it is worth the electrical costs to use HPS lights. HPS lights are known for their yields but what if you could buy LED lights with the extra money you shell out for electricity bills every month?

However, you need to remember that saving money isn't everything. After all, the point is to grow great buds that you can enjoy. You have to question whether LEDs can produce high-quality buds like HIDs. In addition, you have to consider the cons that come with LEDs.

Many companies project the LED technology as the next best thing since sliced bread but we recommend that you stick to what works for you. If you don't mind shelling some extra money every month and are getting great yields with HPS there is no reason to switch just yet.

However, if you are unable to resist the urge of saving money and are getting drawn to LEDs like a magnet, there are some things you should know. LEDs have some benefits that include cost savings, higher efficiency, better light intensity, and more control over the light spectrum that's not possible with HID lights. 

Some modern LEDs can produce healthier plants compared to HIDs. However you should also keep in mind that such lights are expensive, so instead of spending more money on HIDs every month, you'll probably do it in one go with LEDs.

You should also realize that making generalizations about grow lights whether they are HPS or LEDs can lead to bad results. It's not a good thing to compare oranges with apples, which is why many people have disappointing experiences with their grow lights.

Both LEDs and HPS lights have different efficiency ratings which depend on the product. Ultimately there is a difference in the light they produce, which can dramatically affect how the plants grow.

If you want to continue growing with HPS lights or are looking to buy new ones, you need to pay attention to the wattage, type (single or ended), and the ballast. With the technology increasing at a fast pace you will see that the ballasts have improved marginally, which is why some growers stick to HPS lights even today.

Additionally, you must remember that you cannot compare a 400w HPS bulb with a 1000w bulb, although both are HPS fixtures. The key lies in understanding the efficiency they produce. For instance, if the 1000w bulb comes with an electronic ballast while producing a 1.7 µmol/joule efficiency, you can't compare it to a 400 w bulb, especially if it comes with a lower efficiency or even a magnetic ballast. In other words, look for efficiency ratings and the type of ballasts among other things when you purchase HPS. The wattage does matter, of course, but pay special attention to the efficiency rating.

LEDs also work similarly. Although some of them are more efficient than HPS lights and clock almost 2-2.8 µmol/joule, many others don't perform well with low-efficiency ratings. In other words, they produce less light, so the plants don't perform as well as expected. You cannot expect a cheap LED light to perform like a 1000w HPS bulb with a high-efficiency rating, even if you buy a 1000w LED.

Like HPS lights, LEDs also vary depending on their efficiency, diode type, color composition, and other factors. You also have to remember that an LED light even with high efficiency may not perform as expected if the color composition is not perfect for the growth of plants. Therefore, study the document provided by the manufacturer before wasting money on lights. Most growers don't realize that their plants don't produce good yields usually due to bad lighting equipment.

Go for lights that are engineered well and offer better harvests. For example, if you provide LEDs with a good spectrum that will help the plants grow in both the vegetative and flowering stages, you can expect denser flowers and better yields. 

LEDs with good electrical efficiency will also produce less heat which means that you save some money, thanks to a reduction in HVAC use. You'll also need fewer fans and ward off pests that thrive in hot conditions.

So in conclusion, should you switch to an LED light from HPS? As explained above, it depends on your setup. If you don't mind the extra electrical costs and invest in a high-efficiency HPS light you don't have to switch to LEDs. 

However, if you can save up for the initial investment and purchase a high-efficiency LED with a good color spectrum meant for plants, it may be worth your while. LED lights are now not as expensive as before and you can expect to reduce your cost by at least 50% if you go for a really good light. 

It's difficult to compare the costs between LEDs and HPS since it depends on your location (electricity bills differ from one region to another), the number of plants you grow, and your space. But, it all boils down to the yields, so pick something that will last for a while and offer maximum value.

Summary: HID Lighting — A Complete Guide

HID systems have been around for centuries. They provide the perfect spectrum for your cannabis plants and are cheap to buy initially. Although it’s not recommended to use MH or HPS lights individually for an entire cycle, they will work perfectly in tandem if you combine them for your vegetative and flowering stages. 

In addition, they will last for several cycles. If you don’t mind the electricity costs and can reduce the heat with additional fans and an AC, you will find that HPS systems deliver what they promise. Also, note that it’s best to invest in two light models rather than going for one high-power light to prevent hotspots and ensure uniform light distribution.