What is HPS grow light?

HPS (High-Pressure Sodium) lamps are the main choice for cannabis growers all over the world and it is because they produce very intense light that almost no other artificial light source can match. HPS lights work by exciting electrons in a high-pressure sodium bulb. This electron excitement produces a glow that looks like a pink/orange SUN and it radiates quite large amounts of heat. These amazing grow lights have a very high luminous efficacy that means their light to energy ratio – Lumen/Watt (lm/W) is from 100 to 200 and that is quite high compared to some other light sources.

Where HPS is better?

High pressure sodium lamps are good for mid and large scale autoflower growers because small growers will struggle with the heat and will most likely get their plants burned.

Small Wattage HPS light is also good for reasonably small grow spaces because they don’t get as hot as the 600 W and 1000 W bulbs but you still need more room and more ventilation than if you use CFL and LED lights.

So basically anyone who can manage the heat produced from the HPS light will be able to grow autoflowering cannabis plants under these lights and more often than not they will get more yield than from any other light source!

Color temperature

High-pressure sodium lamps produce mostly the yellow light and this lamp light spectrum is mostly at the end of visible light frequency. Because of this altered spectrum, HPS lights are better at the flowering stages of the plant’s life than the seedling phase.

At the start of cannabis life, it needs more blue spectrum light so it could develop healthy leaves, stems, and roots. But when cannabis starts flowering as the Sun turns yellowish red when the summer comes to end and the sun is lower at the horizon.

When the sun is not in the middle of the sky it needs to travel through more dust and other particles that refract and reflect the light so the spectrum is altered and it becomes more Red and yellow! This red color spectrum is beneficial to plants because the small photosynthetic pigments that absorb red light have a bigger influence on flowering than the overall growth.

If an autoflower plant would be grown from seed under an HPS lamp it can get stretched and sturdy as it won’t have enough blue light. Because the photosynthetic pigments that absorb blue light send more energy to stems and leaf, more blue light rather than the red spectrum light is needed for the seedling and vegetative growth stages and because of this growers who usually use HPS lights tend to start plants under MH lamps or fluorescent tubes that can radiate the blue light.


There are various wattage HPS lamps available on the market ranging from 70W to 1500W, but the most common ones used for indoor cannabis cultivation are 150W, 250W, 400W, 600W, and 1000W bulbs.

Basically stronger bulbs promote more growth and are more efficient, but smaller ones are meant for smaller grows and can still be more efficient than CFL or some LED grow lights.


High-pressure sodium lamps heat up the sodium vapor to increase the pressure and achieve the yellowish glow. This heat is a constant distraction for autoflower growers because you need to introduce powerful ventilation systems to maintain the ideal autoflower grow temperature.

For winter grows and grows in colder climates this heat can be beneficial to heat up your growing area to the optimum temperature but usually, the heat is an issue and you will need to install exhaust fans at the ceiling or on the reflector case!

Basically ventilation takes a big part in growing autoflowers with HPS bulbs because you will need to supply ventilation that takes the heat out of the grow room as well as install oscillating fans for air circulations that will blow the heated air away from the plant canopy and allow them to be closer to the bulbs!

Typical space from High-Pressure Sodium lamp to cannabis plants needs to be somewhere from 6 to 15  inches (15 to 40 cm) depending on the lap strength, growth stage, and strain.

For 150 W HPS you can get your plants as close as 6 inches (15 cm) and they will be just fine but for stronger wattage bulbs you will need to increase the distance and the best way to measure the heat is to put your hand below the bulb and if you are comfortable then the plants will also be comfortable at that distance! If you would like to be more specific then you can put a thermometer below the bulb and see the actual temperatures and if it does not exceed 29°C then your plants will be fine!

Another way to combat heat is to get a HPS bulb with a closed reflector case and ventilate the hot air out of your grow room directly from the space surrounding the bulb and don’t let it reach the plants. In this situation, you can get your plants closer and you can get more growth as the light will be more intense!


And running the 600W HPS on a 24/0 light schedule would mean it would chew up 15.6 KW/h ((24 * 650W )/ 1000) every day or 468 KW/h a month that equates to 50.1 $ (468KW/h * 0.10 $ + 3.3 $ ).

To show the approximate costs lets take a middle of the range 600 W HPS bulb with an electronic ballast and a reflector, that package will cost you somewhere around 120 to 150$ and you would also need another bulb as a reserve if the first one fails, so it is another 20 to 50$. So the total upfront costs are around 170 to 200$.

The bulb itself will consume somewhere around the rated 600W of power and the ballast will chew up from 20 to 50 additional Watts so the total Wattage output is around 650W mark. You will need to change the bulb every year and the bulb costs from 20 to 60$ so let’s take the middle of 40$ and divide it by 12 to know how much potentially you would need to invest every month!

40$ / 12 = 3.3$

If you would change the schedule to 18/6 then it would be getting 11,7 KW/h ((18*650W)/1000) every day or 351 KW/h a month that equates to 38.4 $ (351KW/h* 0.10$ + 3.3$)

So considering that autoflower cannabis plants will be ready to harvest in two to three months you will be paying around 125$ for a 24/0 light schedule and about 96$ with the 18/6 schedule!

With this amount of light (600W) you can grow up to 6 plants and get a decent harvest for a price of 100$ in electricity and about 200$ initial investment!

HPS grow light fixure

HPS grow light fixture


HPS light provides more lumens than any other light source but with bigger bulbs and higher wattages, you can get more efficiency (watt to lumen ratio).

Basically lumens are the measurement of light that says how much light is shining on one meter of space one meter away, 1 lumen being the light that a typical candle shine on that same meter.

HPS lights are very powerful and they can have from 30000 up to 140000 lumens.

1000 W HPS light will give off about 140,000 lumens but this is the amount that the light intensity is at 1 foot from the bulb and the further you go the more the intensity drops and around 2 feet away you get 35000 and 3 feet away it is only 8750, so you need to get you plants as close as possible to the lights.

Here are some other wattage and distance to lumen High-pressure sodium bulb charts:



1 feet away 2 feet away 3 feet away
140,000 35,000 8,750


1 feet away 2 feet away 3 feet away
90,000 25,000 5,625


1 feet away 2 feet away 3 feet away
58,000 14,500 3,625


1 feet away 2 feet away 3 feet away
30,000 7,500 1,875

These wattages mean that the stronger lights produce more intense light so you can produce more cannabis plants under intense lights than under the smaller ones. Here are some areas of how much one light can cover and from them you can guess how much plants would fit in there.

  • 150W light can get around 2 x 2 feet(60 x 60 cm)
  • 250w light can get around 3 x 3 feet(90 x 90 cm)
  • 400w light can get around 4 x 4 feet(120  x 120 cm)
  • 600w light can get around 5 x 5 feet(150 x 150 cm)
  • 1000w light can get around 6 x 6 feet(180 x 180 cm)


HPS lamps like any other artificial light source produce light in all directions. All this light is not beneficial to your plants growing just beneath the bulb because they directly get only about 1/3 of the light emitted by the bulb!

If you introduce a reflector you can increase your light intensity and you will get better results and bigger yield.
There are various types of High-pressure bulb reflectors and the typical ones are:

BOX reflector

Box-shaped reflectors are very efficient in directing lumen toward the plants in a smaller area but in greater intensity. These reflectors will grow bigger buds so if you need dense and huge buds then this is your best bet.

Wing reflectors

Wing reflectors unlike box-shaped ones can be adjusted to alter the lumen intensity and light spread.

With these reflectors, you can lose some light efficiency because when the lower intensity light waves reach the plant they cannot be absorbed as well so some of the original light is lost. But overall this reflector is a bargain as you can reach wider areas and if needed you can adjust it for bigger intensity.

Air-cooled HPS reflector hoods

These reflectors that act as an exhaust mount can get the hot air from the bulbs’ surroundings and vent it out directly maintaining good grow room temperature. If this reflector is used then growers can put their autoflower plants closer to the HPS lamp and don’t get heat burns! T

here are several types of these reflector kits but you should know that the glass that doesn’t let the heat out will also decrease the lumen output and the glass thickness and coating will be mainly accountable for how much light will be lost.

Before buying your HPS reflector kit you will need to evaluate your growing situation and know that these complete reflector kits will let your plants to be much closer to bulbs but the bulbs will lose some lumens, so if you have a cold grow room then don’t get the reflector with protective glass, but if your room is hot then a complete reflector kit will be better for you!

HPS cool tube reflector kit

This reflector is made for growers who want really high intensity in a small area and usually is used by commercial large scale growers to get the light really close or closet growers.

Usually, these reflector kits are airtight so the suction is really good and there aren’t many heat leaks. However, this is not the best reflector kit because the glass shell that protects the bulb from getting heat out will bend and refract the light so it will bounce off in odd angles and you will lose some lumens as well!

HPS box reflector hood

This is your best choice if you have one bulb and many plants because this reflector is better for light spread and will illuminate a larger area!

The straight glass will lose fewer lumens and the light will not be reflected, bent so much! These box-shaped reflectors are the main choice for cannabis growers because they lose the least amount of light and their spread is greater.

HPS lifespan and How to save bulbs

Another way to save your bulbs from failure is to leave them on all the time. At first, this sounds a bit controversial, but when you think about it, you get more growth from the 24 hour light period (as I explained in my autoflower light schedule article), and every time you switch on your HPS light the metal at both ends of the arc tube gets a considerable amount of shock by heating up from room temperature to the operational heat. Every time this shock happen the metal can get weaker and a rip or failure can happen.

High-pressure sodium bulbs have a lifespan of about 1 to 3 years and that makes them quite long-living but this lifespan is not the real deal as usually, these bulbs lose their lumen output and after the one year mark you will need to change it to get the most out of your grow!

Usually, growers aim for the 6000-hour life as past that stage the lumen output is decreased and you will be burning the same electricity amount for fewer lumens. HPS manufacturers give their life expectancy ratings for the event when the catastrophic failure is expected but they don’t say anything about the light intensity decrease.

The best way to measure this is to get a Light meter and measure the lumen output at a constant distance after 6 and 12 months of running. If you see a significant lumen output decrease then it is time to change the bulb but usually, it is best to change them every year.

One more good tip is not to touch your bulbs because when you touch something you leave oil and other materials on that surface in the form of fingerprints. When these materials are left on a bulb and it gets hot, they can evaporate cooling one part of the glass and it can easily shatter. You can maneuver your HPS bulbs with gloves or other protection but if you touch them with unprotected fingers wipe them clean before turning ON.

Another way to avoid fractures and failures is to never get water on those bulbs as cold water droplets can again easily stress the glass and it can break. This usually happens when autoflower or regular growers are using hand sprayers for foliar feeding or just to give more water to the plant. You can use hand sprayers if you have an HPS bulb with a complete reflector that has the protective glass shell at the bottom. But if you don’t then it would be best not to spray them!

My last advice is not to move your High-pressure sodium bulbs when they are glowing because the metal at the ends of the arc tube is hot. When it is hot it gets soft and any movement will produce vibrations that can result in dead bulb! This again is controversial as there are some growers who hook up lights on trolleys to mimic the Sun’s movement in the sky but they don’t realize that they are subjecting their HPS bulbs to stress and this way they can decrease their life span.

I haven’t seen any real time application tests that show how much the life span is decreased by each of these stresses, but I think it is easier to take good care of your bulbs and save money doing it!


There are two types of ballasts available on the market and they are Electronic and magnetic. The older magnetic ballasts are noisier, they produce more heat and are not as efficient as the electronic ballasts however they are a bit cheaper but that is their only advantage! Electronic ballasts will run quieter, will produce less heat, and they can even increase your bulbs lumen output and increase the lifespan of the bulbs.

The overall efficiency of the electronic ballasts will give the light-ballast system an average of 10 to 30% efficiency increase over the magnetic ballasts. Electronic ballasts have also the advantage of running multiple light fixtures and that is good for large scale growers as they need fewer ballasts to run the same amount of lights!

HPS grow lamp advantages:

  • High-pressure dodium bulb efficiency is high.

  • They produce a broad spectrum of light.

  • You can get higher intensity from a small bulb.

  • they can warm your grow room in cold climates and in winter.

  • HPS bulbs have a long lifespan.

HPS grow lamp disadvantages:

  • HPS bulbs will need to be replaced every year and that can get quite costly comparing them to CFL or LED lights that last much longer.

  • If you don’t replace them, their lumen output will diminish and you will get less growth for the same amount of electricity!

  • HPS light produces quite a large amount of heat and you will most likely need to install powerful exhaust fans to combat that hot air.

  • HPS lights don’t produce the blue spectrum as much as autoflowers would need and that is why they are not as good for pre-flowering phases, but you can still produce quality buds from seed to harvest under HPS lights.

  • HPS usually is a small bulb that radiates a lot of intense light, and sometimes it is better to spread the light from different light sources in order to get the best penetration and all leaves would get optimum amount of light.


  1. carbonunit dave on

    I do not agree that autos need blue spectrum light from HPS bulbs.In my experience they don’t need blue light at all and do better under red from seed to crop.

    • Good to know that, I think every strain is different and each needs a little different approach but when you think about the light spectrum plants use almost all of the visible light and only green light is not used by them so a more full spectrum light should get better results, but that is only theory and as I told, every strain is different!

  2. doctorspliff on

    sorry, but I use it for my autoflowers bulb HYBRID HPS / MH gives great result (y) 😉

  3. razorbaacks on

    Hi guys,
    I have 2 600w cool tube lights going in my room and I was wandering… well bit of advice really…. can I use 1 hps 600w Dense red spectrum and 1 mh blue spectrum thru out the grow. any advice would be great and many thanks strain will be nl auto

    • Hi razorbaacks!
      I think the spectral mix in both the MH and HPS would give you a more pure white light and make your autos grow faster and stronger. That red spectrum light will give you stronger leafs and denser buds but that blue light will make your auto grow taller and a combination of them both should be nice.
      I think you can start off with just that HPS, and then run them both till the end of the grow.

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