MH and HPS grow lights for marijuana

Often known among indoor marijuana growers as the “golden standard,” HID (high-intensity discharge) grow lights are an excellent option for those new to growing marijuana and those that are experienced marijuana growers.

It has been used successfully for decades, but does that mean that it’s the right choice for you? In this article, we will cover the different aspects — both positive and negative — of MH and HPS grow lights, which are both types of HID grow lights.

CFL lights vs. MH/HPS grow lights

The most likely alternative to MH/HPS (metal halide/high pressure sodium) grow lights is a CFL light. There are pros and cons to both options, so let’s look at the differences between the two so that you can decide which will be best for you and your grow setup.

CFL lights vs. MH/HPS grow lights
CFL lights vs. MH/HPS grow lights

CFLs are best for smaller, stealthy grow areas because they need to be placed close to your plants, making them best for smaller (shorter) areas or strangely shaped ones. They do not cost much, either, so they work well for growers with a small operation who are also on a budget, or else for people who are just looking to get their feet wet in the marijuana growing industry before committing fully financially.

CFLs are easy to find nearly anywhere, so you would not have to order them online. If your setup only requires a few small CFL bulbs, they will not consume much electricity or have a high heat output. This means an expensive exhaust or ventilation system is not so important.

On the other hand, CFLs do not work well for larger growing operations. Anyone who is interested in growing more than one or two marijuana plants should opt for MH/HPS grow lights instead.

The plants under CFLs also need to stay short to get enough light, while MH/HPS lights are known for their penetrating abilities.

The efficiency of MH/HPS lights is much higher than CFLs, giving you a better deal despite the higher upfront costs of MH/HPS lights.

The beauty of HID lights (like MH/HPS lights) is that they are tried and true, having been used by indoor marijuana growers for many years already.

We know they produce great results — there is no question about it. They are also a very practical option.

While CFLs don’t provide much in the way of convenience when it’s time to upgrade your growing area, MH/HPS light fixtures make it easy to do.

Better yet, these lights are some of the most efficient lights on the market (maybe excluding some cutting edge LED lights).

Although CFLs are the common choice for small scale beginners, it’s important to note that MH/HPS lights are nearly as easy to set up and use.

They are user-friendly and are intuitive enough to make the entire process simple for newbies. CFLs are the better choice if you don’t have a tall grow space, if you don’t have enough upfront funds, or if you want something that is easy to find locally.

Additionally, since HID light setups often produce more heat, an exhaust system will likely be necessary to add into your grow space. Check out the best CFL lights at this link.

The different parts of an HID grow setup

Every grow setup that features HID lights should have the following parts:

Parts of an HID grow setup
Parts of an HID grow setup
  • Light bulbs: These will be either MH/HPS light bulbs, depending on the stage of growth your marijuana plants are in, or else they will only be HPS lights for the entire life cycle of your plants.
  • Ballast: This connects the HID lights with a regular light bulb socket. It is necessary for an HID grow setup because these lights aren’t compatible with normal sockets. This will be either magnetic or digital.
  • Hood: This serves as a reflector to help hone all of the light in on your plants below. It is located above or around the light bulbs and is necessary for efficient use of the light energy. Some hoods are also used for the containing and dispelling of heat.
  • Exhaust: This will be necessary to get rid of the hot air in your growing area. It generally includes a fan and ducting to keep the temperature at a healthy level for your plants. It may also include odor control, such as a carbon scrubber or filter.
  • Timer: This works with the lights according to your settings. It will switch them on and off automatically so that you don’t have to.
  • Grow tent (optional): This helps make the walls reflective and waterproof, help with exhaust, protect the plants from leaks in light or from dust, and adds extra security to your growing operation. I highly recommended this.

MH vs. HPS grow lights

Now that you know the different elements that make up most grow setups with HID lights, you are probably ready to buy each part and get started. You will, therefore, need to answer the question: should you buy MH lights or HPS lights?

MH vs HPS grow lights
MH vs HPS grow lights

Essentially you either need to buy MH lights and HPS lights, or only HPS lights. It does not make sense to buy only MH lights. MH bulbs are bright and blueish in color (because they emit light that is mostly in the blue spectrum) to act like the spring sun, making it promote photosynthesis better. Therefore, these lights work best for the vegetative growing period of your marijuana plants.

Download my free marijuana grow guide at this link for more about grow lights

For the flowering stage, however, your marijuana plants are going to need a light schedule that is more similar to the fall sun — the HPS lights, colored yellow or gold (since they are in the orange and red spectrum), are best for this stage. Therefore, many growers opt to use MH lights at first and HPS lights at the end; if you want to do this, just make sure you choose a ballast that works with both lamps. Change from MH lights to HPS lights at the same time that you change your duration of light each day to 12 hours on, 12 hours off to begin the flowering phase.

Using HPS lights alone will still produce good — not optimal, but good — results for your marijuana plants, so for convenience and less hassle you can always use those types of lights.

Some recent reports claim that using both lights at the same time during the flowering phase can actually produce the best results because it is complex enough to be nearer to the sun’s light. This is not officially confirmed, however, so proceed at your own risk. Check out the best MH lights at this link and the best HPS lights at this link.

Buying a ballast

No matter which of the two HID lights you choose from, you are going to need a ballast. That being said, the smaller (150W or 250W) HID lights do usually come with a built-in ballast, so pay attention and proceed accordingly.

Buying a ballast for your marijuana grow light setup
Buying a ballast for your marijuana grow light setup

When buying in concurrence with your lights, ballasts are simple to figure out. If you are going to buy a 400W or 600W light (recommended for beginners), then you simply need to purchase a 400W or 600W ballast. The 600W ballasts are supposed to be the most efficient ones, with the 1000W ballast coming in a close second. Although you probably wouldn’t need to buy one, it is worth mentioning that 150W ballasts are likely the least efficient when compared to their larger counterparts.

The next decision you need to make is whether to buy a digital or magnetic ballast. Magnetic ballasts are trickier because they need to be paired with certain types of lights, while digital ballasts, though more expensive, will save you effort, efficiency, and money in the long run. Digital ballasts are highly recommended. The best type of ballast will be digital, dimmable, and versatile (works for both MH and HPS bulbs). The more expensive the ballast, the longer it will probably last, so don’t skimp on the price.

Buying the bulbs

It’s important to note that, when buying HID light bulbs, you should never buy used ones as they won’t last for long enough. If you bought a ballast that is digital and dimmable, you need to make sure that the bulbs you buy support those features. The best bulbs should last between one and two years although you should probably replace them after 3-4 grows anyway because they will dim over time — even if your eyes aren’t able to perceive this dimming.

5 HID light bulbs
Buying bulbs for marijuana grow light setup

HID bulbs degrade the quickest from being switched on or off rather than from burning for long periods of time. Always avoid turning on an HID light that hasn’t cooled off properly since the last time it was turned on. Double check the specifications on the bulb and the ballast to make sure they match up, or else you could blow the bulb right off the bat. Be sure that there is some sort of exchange or return policy from the place where you bought the bulbs just in case the worst should happen.

When deciding on which “size” of bulbs and ballast to buy, think about the number of plants you are trying to grow. For instance, if you would like to grow between 3 and 5 plants, you should have a bulb (and ballast) of 250W, placed 6-8 inches away from the canopy. For growing 6-9 plants, choose a bulb with 400W and place it 9-12 inches from the canopy. For 9-12 plants, buy a lamp that is 600W and put it 12-18 inches from the canopy. For a growing operation of 12 or more, you will need at least 1000W that should be placed between 18 and 26 inches above the canopy. Use the hand check (see below) to confirm that this distance is indeed good for your plants.

Also read Led lights for growing indoor marijuana

When buying your bulbs, make sure they are coming from a reputable brand. Many products are good at sounding impressive, being labeled things like “full spectrum” and “dual spectrum,” but that might mean nothing if it’s not from a brand you can trust. Some of the leading brands for grow lights are iPower, Lumatek, Sunmaster, Hortilux, Solaar, Philips, Osram, and Sylvania. There are surely other good brands out there, so do your homework before buying a bulb.

Buying a hood

The most important thing to consider when choosing a hood for your setup are the seal, the ease of opening, and how wide and smoothly curved the reflector is. The seal should be just about airtight so that there is ventilation without any odor problems. The hood should be easy to open so that lights can be easy changed whenever necessary. A wider and more smoothly curved reflector will perform the reflecting feature the best, doing so evenly for a healthy grow area.

Reflector hood for your marijuana grow light setup
Reflector hood for your marijuana grow light setup

There are three main types of hood that you should think about buying: winged reflectors, cool tubes, and air-cooled hoods. Winged reflectors have lots of surface area and, therefore, are great for the reflecting part of their job; they aren’t as good with keeping cool, however. Cool tubes are better at keeping cool, but have a smaller reflector and, therefore, aren’t as good on the reflecting side of things.

Air-cooled hoods are the best of both worlds, as long as you take advantage of their handy design feature to easily be hooked up to an exhaust system. They will trap the heat right near the bulb so it doesn’t reach your plants, and then will be sucked out through your exhaust system. Generally speaking, air-cooled hoods (the wider, the better) are the most popular and most effective choice for indoor marijuana growers with an HID light setup.

Hanging your grow light

There are multiple ways of hanging your grow lights. Distancing the lamps correctly is a challenge in itself.

Read more about the best distance for your grow lights.

The cost of your HPS grow light

Figuring out how much running your grow lights will cost is a critical step for growers on a budget- or just about anyone, for that matter. Use the following information to accurately establish how much an HPS grow light will cost you to run.

First of all, you will need to figure out how much your electricity costs per unit. You should be able to find this on any electricity bill you have received, marked as price per kilowatt hour (kW/h). This basically means that you are paying this much to use one kilowatt (1000 Watts) of electricity for one hour.

Let’s say this unit price is 12 cents per kW/h. That means that, if you have a light that is 1000W, it costs exactly 12 cents per hour to use when it is turned on. A 600W bulb would use 60% of that price, which in this example is 7.2 cents while a 250W bulb would use just 25% of that price (3 cents per hour). Calculate the cost per hour for the bulbs that you have.

Now take that number and multiply it by the number of hours you run the HPS per week. Don’t forget to also add in the wattage of the ballast. For example, if you have a 1000W bulb and a 100W ballast, that would be 1100 Watts per hour, which would cost 13.2 cents per hour for this example. If you have the lights running 24 hours a day (like during the vegetation stage), this means it will be $22.18 per week. Flowering (half of the day with lights on, half with lights off) would cost $11.09 per week.

Once you have this information, you should be able to budget accurately. While HPS lights are certainly more expensive to run than other kinds of lights, the effectiveness and proven quality of these lights makes it well worth it for many growers nonetheless. If you are looking to cut energy waste and costs, however, you should consider LED lights instead. More about setting up grow lights in my free marijuana grow bible.

Setting up an exhaust system

An efficient exhaust system is there to both lower the temperature of a brightly lit grow room as well as keep the odor problem to a minimum. When building an exhaust system, there are a few important elements to consider. For example, remember to keep the temperature between 70 and 75 degrees Fahrenheit during the “daytime” (lights on) and 60 and 70 degrees Fahrenheit during the “night time” (lights off).

Setting up an exhaust system
Setting up an exhaust system

The entire air within the grow room needs to be replaced every 1-3 minutes. Keep this in mind while designing your exhaust system. If you take the time to completely understand the flow of air in the room as it is already, you should be able to make a much more efficient exhaust system than if you didn’t know much beforehand. You should also use a fan along with the exhaust system to make sure that it works as thoroughly as possible.

Know how to perfectly time your harvest so you can maximize your yield. Download our free mini harvesting guide

To calculate the strength of the exhaust fan, you will need to figure out the appropriate “CFM” (cubic feet per minute) rating for your grow area. You only need to multiply the cubic area of the space (length x width x height) by 2 if the exhaust path is efficient (no bends or turns, but a short, straight route), or by 3 for an inefficient one. Then use the resulting number to choose an appropriate fan that has that same number or higher.

You should also consider the intensity of the lights you are using. Make sure to do the research to determine the total the appropriate fan for the wattage of the light and the area of your grow space. When in doubt, use a larger exhaust fan than you think you need.

Also read How to build an indoor marijuana grow room

The best type of fan for indoor growing areas is an internal circulation fan to keep a constant flow of air around the area. This will help the temperature remain stable and will bring in fresh air with CO2. Fans placed beneath the lights are perfect.

The strength of your exhaust system may also depend on the type of lights you are using. If you are using a 400W HPS grow lamp, for instance, the temperature of the room could be raised by as much as 15 to 30 degrees Fahrenheit.

The stealthy exhaust method
If you would like to design an exhaust system that is particularly stealthy, there is one inexpensive and simple method that will definitely do the trick. All you need are wicker blinds, foam, corrugated plastic, duct tape, ducting, super glue or hot glue, and a staple gun. Hang the wicker blankets over the window where you will send the exhaust from as the air can get through without allowing people to see in and become suspicious. Glue the corrugated plastic to a large piece of foam, then trace around the ducting on the layer of foam and plastic to cut out a duct-sized hole. It should be somewhere towards the top.

Next, put the ducting through this hole until it is right against the blinds. Tape the foam and plastic layer there, right over the window, using duct tape. Staple the duct tape in place for added security later. The combination of the foam and plastic will mute the sound while the wicker shade will prevent it from looking like anything but a normal wicker shade over a window, without causing suspicion.

Thanks for reading. If you want to start growing, download my free marijuana grow bible and order some marijuana seeds. All top quality marijuana seeds are available in my marijuana seed shop. We ship seeds all over the US. For any grow related question please visit the marijuana support page.


Avatar for Robert Bergman

Mr Robert Bergman PhD


Robert Bergman is an Amsterdam-based marijuana grow expert who has years of experience from small grows to massive operations ... See profile

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30 comments on “MH and HPS grow lights for marijuana”

  1. What would be a good substitution to say that you are growing with this setup? What other herbs, or vegetables flower during a shorter photoperiod

  2. Did you mean to say “if you can’t stand the heat”? In your text you said “can”

    In order to check this, simply hold your hand underneath the lights for ten seconds near where the tops of your marijuana plants are. If you can stand the heat, this is too hot for your plants and you should move the grow lights up, further away from them.

    The following distances will be useful when you are initially estimating what the distance should be.

  3. I was us a viparspectra 300 led Before i bought a wills cree Cob 1000 watt led. And this thin is a beast for just $140. I’m so impressed that im buy a wills 3000 watt led for my 7×8 grow room. One should be fine i would think. But im going have 2 of them. The 1000 is so bright that it burns my eyes with sun glasses

  4. I wanted you to edit your description of a hand check, it currently reads if you can, and should read if you can’t. Otherwise an awesome read…

  5. oehawk

    2 400w HID lamps in a 3×3′ tent may be a little too much. It is OK to combine MH and HPS in one grow area.

    If you have
    AC and good ventilation in your tent, you might get AWAY WITH THIS.

  6. Ok you know 12 on 12 off (as dark as possable) do not let more than a fingernail moons light in. To trigger a flower stage you can keep them in the dark for 24 to 48 hours iv herd of plp. Going longer but i just use 12. 12. Try to keep you lighting temperatures as low as possable. I use a fan on a a/c register box thru the ceiling

  7. LSM,

    You will have to Air condition the room outside your grow so that you can bring in cooler air. Other than that; “You might need a bigger exhaust system. Perhaps it would be helpful to you if you joined our forum. Many helpful opinions and friendly advice. See you around. 🙂

    Happy growing – I❤️GM

  8. I have a 4×4 room, a 400 watt MH and a 600 watt HPS. I am using the 400 watt right now and when I close the door it still gets too hot in there. I have a ventilation system and a fan too. What else can I do to get the temperature down?

  9. oh and to ilgm <big ups to u guys for my seeds as they came in on the 20th day ,and i had them popin overnight ,i didnt think that the seeds were coming either, but yay

  10. dear robert and claire,, hi its dot here, i have been trying to find out wot to do about my plants, i have a pest , {mealybugs } i think bt am not sure but they have made a mess , i have used conquour oil on the problem but so far they just look worse . i have to sort smthing out as i have babies going aswell .i hv a tent that is 1.8 sq, and have a 400 light , i used this setup for the blue dream and got wonderful results,i buy everything new so cant understand why the bugs,, any help would be awsm .. plz help ….

  11. […] is why it is so important to choose lights that have a full spectrum. HPS lamps, or high-pressure sodium lights, for example, do not include the right amount of blue light and therefore will lead to unhealthy […]


  13. Doc,

    We never recommend a 24 hours continuous light cycle. Plants like humans need rest and lights out. Rooys grow more aggressively in dark periods. I actually veg “feminized seeds under 16/8 to start. The most aggressive root development occurs when the plants have 10-12 hours of uninterrupted dark period. Hard to sell to some growers but, it is true.

    You can use all the light you want in flower. You do have to plan to refresh air through a ventilation system in order to remove hot and stale air from the grow space.

    A proper ventilation system is required and will remove hot air and replace it with fresh air. Join our forum if you would like to learn more on this topic, from our members and experts. Look for you there! 😀

  14. Robert,
    Thank you, for sharing your knowledge, it’s a shame more people do not take the time to do the same. I would like to know if you prefer a 24 hour light schedule in veg versus an 18/6. I currently possess a 400watt MH, I want to add an 600watt HPS. Can I use them simultaneously during the flowering stage? I have up to 100sqft of available space, I am currently only utilizing 9sqft to pop my cherry. I have 4 bag seed Mexican sativas in soil. They are just beginning pre flower and are all girls. I using Happy frog and FF trio for nutes. Following the FF feeding schedule. So far everything is beautiful, I’m just not sure about the lights in flowering. Thanks for any reply.