MH And HPS Grow Lights For Marijuana

Indoor grow light set up
September 09, 2020

HID (high-intensity discharge) is the “gold standard” of indoor grow lights. No other type of lighting can match its yield per watt output. For decades, the most discerning marijuana growers and breeders have relied on it, and so should you. As it has become mainstream, the prices of the two most commonly used HID lights – MH and HPS – have gone down. Once prohibitive, you can now purchase them at reasonable costs.

The Progression From CFL To MH/HPS

Yes, some people do start growing marijuana using CFL (compact fluorescent lamp), mainly for a couple of reasons – both having to do with cost. These bulbs are cheap and widely available.

  • Some people are not sure if they would continue growing marijuana. Starting small using CFL lets them try it out without committing a significant investment.
  • If money were not a concern, then there is no reason to use CFL lamps. MH and HID are superior, but they do cost a small fortune, which some people cannot afford.

CFL lamps are not without good uses. For example, they are excellent for growing one plant, especially if stealth is a necessity. In some cases, growing only 1 or 2 plants could be a matter of limitation in the size of the growing area. They can fit in well inside a cupboard or a small closet, and not produce excessive heat. Some people also use CFL for seedlings before transferring them into an HID-fitted grow room as the plants enter the vegetative stage.

At some point, anyone who decides to continue growing marijuana or increase the number of plants should use MH and HPS lamps. Yes, the upfront is going to cost a few hundred or even over a thousand dollars. However, they will give you your money’s worth over the long term. More importantly, HID bulbs make it possible for you to cultivate plants to their full potential.

MH/HPS Marijuana Grow Lights

The cost of HID lamps is not the only concern of many beginners. They also seem complicated to set up and use. In reality, choosing from the plethora of brands available may be more confusing than the actual installation and operation. Sure, MH and HPS lamps require other pieces of equipment to function. Once you have figured out what you need, installing in the grow room is not difficult, but takes a bit of time.

Should You Choose MH Or HPS?

The short answer is both. These two – MH and HPS – are both HID lamps that serve different purposes. One is used for the vegetative phase, while the other is for flowering. For more information on making the best decision, check out A Beginner’s Guide with Kyle Kushman Episode 3: Choosing Your Lights and see what master cannabis cultivator Kyle Kushman thinks are the best grow lights.

MH (Metal Hydride)

During the vegetative phase, the Phytochrome Far Red (Pfr) receptors of plants prevent them from flowering. Therefore, it is of utmost importance that the plants receive a spectrum of light that promotes growth but inhibits the conversion of Pfr into Phytochrome Red (Pr).

At this stage, you do not want to have anything to do with Pr, which is why the plants should not be exposed to a reddish light spectrum. Instead, what they need is the bluish light emitted by MH bulbs that promotes the healthy development of the root system, stems, and leaves.

HPS (High-Pressure Sodium)

Once you switch to a 12/12 light cycle to trigger the flowering stage, you would change from MH to HPS. It emits a reddish light spectrum that mimics autumn sunlight, telling the plants to begin their reproductive phase. Except for the new generation of LED marijuana grow lamps, no other lighting type comes close to HPS in promoting the production of dense buds and abundant trichomes.

What Else Do You Need Besides The HID (MH+HPS) Lamps?

For CFL bulbs, all you need is a socket and a switch. That is not the case with HID lights. You will need a ballast, hood, exhaust, and timer. In a nutshell, these are their functions:

Ballast. Acts as a power transformer that provides clean, high voltage electricity to initiate arcing (turning on the HID lamp). For convenience, choose one that is “switchable” – one that can power both MH and HPS bulbs. It should also be dimmable and uses a microprocessor to monitor and regulate voltage.

Hood. The lighting fixture for HID lights should have a reflectorized hood. Its primary purpose is to deflect light downwards to the plants to not waste light energy directed away. Some models also serve a secondary function – containing in dispelling heat.

Exhaust. HID lamps generate a lot of heat. To keep the temperature cozy, you would need to invest in an exhaust fan that removes warm air from the grow room. An optional accessory that you could attach is a carbon scrubber to eliminate the odor of marijuana from the air before expelling into the open.

Timer. Religiously adhering to the light on and off schedule is one of the fundamentals of healthy growth. A timer helps you automate a tedious task.

The Marijuana HID System Trinity

To focus only on MH and HPS is to ignore the other critical components that make an HID grow room work. An injustice is what it is. Now is the time to learn more about the bulbs, ballast, and hood – to know what you need.

As a general rule, you should go for high-quality products. There are plenty of ways to cut costs, but the lighting system is not one of them.

What MH And HPS Lamps Do You Need For A Marijuana Grow Room?

MH lamps produce light once an electric arc passes through a vaporized mix of gases such as argon and mercury. These bulbs can deliver 75 to 105 lumens per watt, mimicking the sun’s light spectrum during spring. Usually, they would have a lifespan of 10,000 hours. Towards the end of the life cycle, though, their light intensity lessens. Hence, it would be better to replace them halfway through the rated life cycle to ensure your plants receive optimal light intensity.

In principle, HPS produces light the same way MH does, except that it uses sodium gas. It creates a wavelength that stimulates plant hormones, triggering them to produce buds and trichomes. These bulbs can provide 130 to 155 lumens per watt and have a longer lifespan than MH. Typically, they would last 18,000 hours. Like MH, their light intensity also diminishes over time.

HID light bulbs may last up to two years. For marijuana cultivation, they deviate from the usual practice of replacing once busted. Once they reach more than 50% of their life cycle, the light intensity diminishes, resulting in less prolific growth. To be clear, the degradation rate is not due to the hours of operation. Instead, it is by the number of times they were switched on and off. Hence, you should replace them after 3 or 4 grows, even if they appear to be working.

When buying MH and HPS bulbs, you need to consider the planned number of plants and the size of the growing area.

Wattage Number of Plants Growing Area (ft)
150 1-2 2 x 2
250 3-5 2 x 2 to 2.5 x 2.5
400 6-9 3 x 3 to 3.5 x 3.5
600 10-12 3.5 x 3.5 to 4 x 4
1000 13+ 4 x 4 to 5 x 5

As you can see from the table above, you only need 250 watts if growing only 3 to 5 plants. And for 6 plants (the legal limit in most states that allow home cultivation), you are better off using 600 watts.

You should also consider the size of the growing area. If you choose 600 watts, for example, then you need to have a 3.5 x 3.5 to 4 x 4 feet space for the plants.

An excellent electronic ballast should be dimmable, so make sure that the HID bulbs you choose are compatible. During operation, a simple thing you can do to prolong their lifespan is to avoid turning on a lamp that has not cooled down since being turned off.

Are you ready to buy? Wait, there’s also the matter of single-ended or double-ended bulbs.

If you already have a reflector hood, then pick bulbs (MH and HPS) that fit. In a nutshell, single-ended bulbs are the cheaper option and generate less heat. On the other hand, double-ended bulbs provide more output, last longer, and emit more heat.

Which Ballast Should You Buy For Your Marijuana Grow Room?

For starters, you are most likely to invest in 400 watts HID lamps. It is more than enough to support the maximum limit of 6 plants when growing at home. As far as power goes, picking a ballast that matches your preferred bulbs is a no brainer. With regards to efficiency, 600 watts ballasts are more ideal, with 1000 watts coming in second. As for 150 and 250 watts, they are the least efficient.

In the past, the most common type of ballasts were magnetic. Those can be challenging to use and work with specific types of lamps. Instead of scrimping, choose a digital ballast that is dimmable and works with both MH and HPS bulbs. Although more costly, they will last longer, for sure. Not to mention, you will also have an easier time working with them.

What Kind Of Hood Do You Need?

There are three things to consider when choosing a hood – seal, ease of use, and shape. Moreover, you have three main types to choose from – winged reflector, cool tube, or air-cooled.

A typical HID setup includes the hood connected to an exhaust fan via ducting. You want the hood to seal properly for the efficient removal of warm air from the growing area. Its design should be that it is easy to replace bulbs or perform other maintenance tasks. Lastly, a large, smoothly curved reflector can best deflect and distribute light to the plants evenly.

As for the type of hood, a winged reflector has the broadest surface area and is excellent at directing light towards the plants. However, they are not efficient in keeping the temperature down. Cool tubes, on the other hand, are better at controlling the temperature. Its small reflective surface, though, does not perform well.

An air-cooled hood is your best choice. This type of hood is what you need to install ducting, and hook up with an exhaust system. It traps heat generated by the lamp, keeping the plants cozy. An exhaust fan then sucks it and expels outside the grow room.

Air-cooled hoods offer you the best of both worlds – directing light to the plants while helping keep the temperature manageable.

Setting Up And Using Your MH/HPS Lights

Instead of buying the HID components one by one, you can opt for sets. Reputable brands often would have pre-configured sets that include the lamps, ballast, and hood. They are not challenging to install in the grow room. Follow the installation manual, and you are good to go.

Once in use, the only concern you have that requires your immediate attention is making sure the plants receive optimal light without getting burned. You should also perform a hand test. Place your hands above the plant canopy for 10 seconds and feel the heat. If it is too hot, then that is how your plants feel, and you should increase the distance.

Wattage MH (inches/cm) HPS (inches/cm)
150 4-10 (10-25) 4-12 (10-30)
250 5-13 (12-33) 5-15 (12-38)
400 7-18 (18-45) 7-21 (18-53)
600 10-27 (25-68) 10-28 (25-71)
1000 12-31 (30-78) 12-35 (30-88)

The table above is only a reference, a starting point. It is incumbent upon you to find the best distance. Move the lights further up, for example, and cover a wider area, but that comes at the expense of lesser light intensity. As an option, you may invest in a lux meter to measure the brightness from different distances. For healthy vegetative growth, the plants would need 15,000 to 70,000 lux, with 40,000 being the most ideal. Once in the flowering stage, the light intensity should be between 35,000 to 85,000 lux, with 65,000 being the most ideal.

The Cost Of HID Grow Lights

You can estimate how much it is going to cost when using HID lights. All you need to know is how much electricity costs per kilowatt-hour (kW/h). You can find this in your electricity bill.

A kW/h means you pay for X amount of money to use one kilowatt of electricity for one hour. So, if the unit price is 12 cents per kW/h, and you are using a 1000W bulb, it would cost 12 cents per hour of use. A 600W bulb would cost 60% of the rate (or 7.2 cents/hour), a 250W bulb would cost 25% (or 3 cents/hour).

Besides the bulb, you should also factor in the electricity used by the ballast. Using the above example, if your 1000 watts ballast uses 100W of electricity, you would be consuming 1100W. At 12 cents per kW/h, that would be equivalent to 13.2 cents per hour.

Next, compute the number of hours. During the vegetative stage, you would have the lights turned on 18 hours a day. That would be 13.2 x 18 hours = $2.38 per day or $16.7 per week. The flowering stage would be 13.2 x 12 hours = $1.58 per day or $11.06 per week.

Note: The above-cited figures are for 1000 watts.

MH And HPS For Your Plants

An HID light system will produce the best results for you. Yes, initially, you would have to spend on the equipment. Moreover, your electricity bill will surely increase. All these costs – investment and operational – may seem like a dealbreaker. As many growers know, the upside more than makes up for the money spent.

If you want to grow the healthiest marijuana, harvest the most buds – and potent ones – grow with MH and HPS lights. Once you have the stash in your hands, its value would far outweigh the costs.

If you’re looking at growing cannabis using MH lights or HPS lights and still have any unanswered questions why not head over to the Homegrown Forum and see what advice fellow growers in the Homegrown community can offer. Furthermore, if you encounter any problems with your lights while growing marijuana, then ask your questions in the lights and ventilation category of the Homegrown Community Forum.