How to Choose HPS Grow Lights for Growing Cannabis

Last updated Oct 13, 2023

by Nebula Haze

Feel free to check out my main page about cannabis grow lights! This page talks just about HPS grow lights while the other page covers all cannabis grow lights.

High Pressure Sodium grow lights, or HPS grow lights, were the golden standard in growing cannabis indoors from at least the 70s to the early 2010s. However, modern LEDs are getting comparable and even better results, especially for certain setups and cannabis strains. However, HPS grow lights have some unique advantages for growing weed.

High Pressure Sodium grow lights, or HPS grow lights, were the golden standard in growing cannabis indoors from at least the 70s to the early 2010s. However, modern LEDs are getting comparable and even better results, especially for certain setups and cannabis strains. However, HPS grow lights have some unique advantages for growing weed.

Are HPS grow lights good for growing weed? Yes. HPS lights can be used for the entire cannabis grow from seed to harvest, though many growers like to start with a Metal Halide bulb in the same fixture before the cannabis hits the flowering stage because the MH bulb encourages cannabis plants to stay shorter.

HPS grow lights tend to produce some of the best cannabis yields of any grow light, though only when kept in a relatively cool grow space. HPS grow light fixture are cheap, so they cost less to start growing than LED panels, which tend to cost more for the amount of weed they can produce. However, HPS lights use a lot of energy and make a lot of heat that usually needs to be vented from the grow space. The bulbs aren’t that cheap yet need to be replaced every few grows. That means HPS grow lights cost more in the long run than LEDs. If you’re a beginner grower, keep this all in mind before choosing HPS grow lights.

HPS grow lights produce a harsh yellow light. Read the Complete Guide on HPS Grow Lights!Give your cannabis plants plenty of light in the flowering stage, and keep grow lights close enough

Pros and Cons of HPS Grow Lights

Pros

  • Excellent yields – With the right environment (not too hot), HPS grow lights may get the best yields of any grow light. Bud grow big and fat under HPS.
  • Plants can resist the cold – Performs well in cool grow space that is consistently under 80°F with lights on. On the flip side, LEDs perform poorly in a cooler grow space.
  • Cheaper to start (for bigger grows) – Compared to LEDs, buying the actual HPS grow light fixture is cheaper for the wattage and expected harvest. If you want to grow a pound of weed, it costs half as much to buy a suitable HPS grow light setup than a comparable LED one. However, this doesn’t take into consideration the cost of running the HPS, which will change the equation long term.

Cons

  • Very Hot – HPS bulbs produce a lot of heat that radiates outward from the bulb.
  • Big electricity bill – Use a lot of electricity to run the lights, as well as to run powerful fans or an AC to vent heat and keep the grow space cool. Tends to be more expensive than LEDs in the long run.
  • Must replace bulbs – You need to replace your MH/HPS bulbs every few grows or they become less and less bright (effective) over time. This is another cost that can start to add up after a while.
  • Ugly yellow light – The garish yellow light looks old-fashioned and plants don’t look as beautiful since you can’t see their color. The lack of color can also make it harder to spot problems.

If you’ve got a grow space that naturally stays cold, HPS might be the best choice. No grower wants to spend money heating a grow room so the LEDs work properly. But other than that, you will save money long-term by investing in a high-quality LED grow light, even though it costs a bit more up front.

Ideal Grow Environment HPS Grow Lights

HPS grow lights are extremely well suited for grow areas that have…

  • Good Ventilation – HPS lights will heat up an area. That means in order to maintain cool enough temperatures, most growers need to vent heat out a window or use an AC
  • Bigger Grows – The 600W HPS grow light is the most efficient HPS grow light. Great in a 4’x4′ grow tent, and can produce a pound or more.
  • Need 6’+ vertical space – At least 6 feet of height (up-and-down room) for the cannabis plants to grow. These aren’t great for growing in limited-height situations.

HPS grow lights are not as well suited for grow areas that have…

  • Not hot or stuffy – HPS does poorly when there is little ventilation or no way to get air in and out through a hole or window. The area will get too hot for plants
  • Can’t use in a short space – You can’t use HPS when there is limited vertical space (such as inside a cupboard). If you have a small grow space, your best option is a small LED light the Spider Farmer SF1000 (100W LED grow light).

Another consideration when using HPS lights for a grow area that has a natural temperature that is higher than 65 degrees(F) or 18.3 degrees(C), is that you will need to set up some sort of exhaust system to control heat. A simple exhaust system that consists of some tubing/ducting and an exhaust fan will do the trick most of the time. As long as you have a way to get air in and out of the grow area, you’re golden.

Example of setting up a full exhaust system with ducting connecting the grow light to the fan

Learn how to easily vent out heat from your HPS grow lights

Setting up an HPS system takes careful planning because you generally need to buy more than just the bulb, reflector, and ballast. In most cases, you will need to set up some sort of ventilation system with an HPS grow light, even if it’s as simple as a fan pulling hot air away from the lights and venting that air outside. Many set up simple ducting systems to manage the hot air. Just remember to make your intake hole bigger than your exhaust hole or you may cause your fan to struggle! This is especially important in a small or airtight grow area because the exhaust fan will be working extra hard to get enough air through the intake hole unless the intake hole is bigger than the exhaust hole in size. In general, when setting up your HPS system, you want to set things up so the hot air from the HPS are blown directly out a window or some other escape with as short a path as possible. This will help make the exhaust system more efficient. You may need to set up a carbon odor scrubber to eliminate any smells before they reach outside. More info on buying a carbon odor scrubber to control the smell of cannabis below, or read the carbon scrubber tutorial.

Digital Ballasts vs Magnetic Ballasts

While magnetic ballasts are cheaper, a digital ballast will start up more quickly, run silently, produce less heat, last longer, and even produce more lumens (light) than a magnetic ballast. More light means more yield and digital ballasts can somtimes produce 20-30% more light than a similar bulb on a magnetic ballast. What’s more, a digital ballast may extend the life of your bulbs so you have to buy new bulbs less often. There really is no comparison in quality between a digital and magnetic ballast, the digital ballast is just better. A magnetic ballast can take up to 20 minutes to start up, and tends to run noisy and inefficiently while producing less light and burning through more bulbs. If at all possible, spend the couple of extra bucks and get the digital ballast!

Learn more about using HPS grow lights when growing cannabis.

Get Started Shopping for HPS Grow Lights Today!

I hope the product links below can help get you started so you can see some concrete examples of what sort of cannabis grow lights are recommended. The grow light systems and growing accessories on this list were specifically chosen for quality and effectiveness.

A full grow light system contains a ballast, a reflector/hood, a bulb, cords and plug, and some systems even include the hanging equipment. I personally recommend starting with a full light system that is made to go together as opposed to trying to buy all the pieces separately and put them together. Whenever you are buying from any grow light seller, make sure that they are a reputable seller and not some guy selling lights out of his garage. There’s nothing worse than spending hundreds of dollars for equipment that is broken or doesn’t work properly. When buying from unrespectable sellers, you may run into customer services issues if you need to return something. I personally like Amazon.com because they have a great return policy and will stand behind you, the customer, if there’s a problem with one of their sellers.

400W MH/HPS

Average Yield: 7-14 oz Per Harvest

Cost: $495 to start

 

600W MH/HPS Grow Setup

Average Yield: 10-21 oz Per Harvest

Cost: $495 to start

Grow Tents

Some growers choose to use a grow tent to be able to better contain and control the heat. You can set a fan to expel hot air directly out of the tent to a window or other vent. Make sure to allow enough vertical (up-and-down) room for the HPS, the plant, and 1-2 feet of extra space that will need to be between the light and the top of the plant when it’s at full height. Remember 60 inches = 5 feet.

Learn about cannabis grow tents

You May Need an Inline Fan with a Carbon Scrubbers to Remove Odors

Learn about carbon scrubbers and removing smells

 


Read the Complete Guide to HPS Grow Lights!


 

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