Last updated: June 30, 2020
It wasn’t all that long ago that proponents for the use of LEDs for indoor grow lighting systems were being scoffed at by the old pros that lurk the forums. They were too expensive and gave sub-par results in a lot of cases when compared to the standard HPS (High Powered Sodium) lamps that were easily available. Yet, others believed in the technology and that in the near future HPS would finally meet its match.
We are now in that era. The choice between LED and HPS systems has become quite muddled with LEDs now proving themselves as a solid and respectable choice for an indoor grow light set-up.
It’s true that both lighting systems are capable of growing plants when used properly. However, the way these technologies achieve this goal is actually quite different.
An HPS system is actually a subcategory of HID (High Intensity Discharge) bulbs. These operate through the heating of gases within a tube, sort of how fluorescent bulbs operate. The other common HID bulb used for growing is a MH (Metal Halide) bulb, which tends to be used instead of an HPS light during different stages of plant growth due to the two gases gases giving off different wavelengths of light when heated. HPS tend toward the red spectrum, while MH lean toward blue spectrum of light.
Due to the nature of heated gases, these lighting systems achieve a fairly high temperature when left on for the length of time plants require during certain stages. On the other hand, these systems are very luminous and have very little difficulty ensuring enough light reaches the plant, so long as proper cooling and ventilation is in place.
LEDs operate on a different principle entirely. The term stands for Light Emitting Diode, and it operates via current passing through a semiconductor. As the electrons pass through that semi-conductor they emit light, generally of a single wavelength. LED light systems are composed of many semiconductors capable of different wavelengths that can combine to create a range of colors dependent on what is needed.
As LEDs create light a bit more directly than the aforementioned HID systems, they tend to be a lot more electrically efficient as far as power bills are concerned. They do still create a decent amount of heat for their size and may need to be cooled when used at length, but in comparison to giant gas tubes it can be a lot easier to manage.
There are a few pretty distinct differences between LED and HPS systems just because of how they produce light.
An HPS system is hotter, as we already discussed, but this is actually compounded by the need for reflectors above and to the sides of the tubes. The gas tubes produce light in a 360-degree radius, causing much of the needed luminosity to be spread out everywhere across the room except onto the plant.
The solution to this is a reflector panel. These mostly come in the form of large, curved, metal housing units that surround an HPS tube on all sides except the bottom, redirecting the majority of the available light downwards as well as the heat.
This can cause the need for cooling systems to be in place, as ambient temperatures can get quite high if the grower isn’t careful. Do note that this can actually be a benefit when growing in a colder climate.
Setups using HPS systems generally have to measure out the appropriate distance between the plant and the light to find the placement that has the most amount of light reaching the plant, without causing issues from overheating.
LEDs may also use reflectors in certain cases, but more of a redundancy than a required piece of hardware. LED systems tend to be flat panels that hang a fair bit closer to the plant.
Without as much heat concerns LED systems don’t have the issue of light spreading and diminishing due to distance. This also means that LED systems can actually produce less total light while having similar amount of lumens reach the plant. Efficiencies such as this are the name of the game when it comes to LEDs.
LEDs also last quite a bit longer, and the quality of light produced stays pretty consistent throughout their lifespan. HPS systems require a replacement after about 12 months, once they start dimming, as the quantity of light diminishes through the process of burning out.
Lower electrical bills and lower replacement costs through LEDs, mean they are actually cheaper in the long-run than an HPS system which tends to be cheaper in its upfront cost.
When talking about plant growth two light spectrums come up in conversation often, blue and red. These are ways of describing different tones of visual light, but also the non-visual that affects the growth of plants.
Blue light is associated with the Summer months, which corresponds with seedling and vegetative stages for plants. Blue light is readily photosynthesized by most plants during these months, and allows for healthy, strong growth.
Red light, then, corresponds with the Fall. Using red lights on a plant can shift them into their flowering stage once they are matured. Red, however, is not as easily photosynthesized by plants, making it sub-par for vegetative and seedling stages.
All this is to say that the type of light being produced by a growing setup really matters a lot, with different light types being better at producing different spectrums.
With an HID system, a lot of growers switch between MH and HPS tubes depending on which stage of growth the plant is in. MH lights produce in the blue light spectrum, so it is best used during earlier stages of development. HPS produce more on the red-orange spectrum, so they are best used during the flowering stages.
HPS lights can also technically be used for the whole period, but the younger plants have more difficulty processing red light than blue, so insufficient lighting issues can occur unless properly accounted for.
LED systems counter the issue of having to change lights by offering both red and blue spectrums via running an adjustable chip that allows for the colors to be changed at the grower’s discretion.
Though this is highly convenient, there is debate about the quality of light being produced. Much of the light being photosynthesized by plants is actually not within the visible spectrum. Precaution should be used when growing plants under LEDs to ensure a true red and blue spectrum is being produced by the system, instead of just blue and red visually.
Quality manufacturers make sure of this, but lesser products can definitely have this issue. HPS and MH lights, on the other hand, are guaranteed to produce the proper light spectrums.
This is the most vulnerable stage of growth for any plant. Because of this, HPS lighting systems tend to have some trouble.
The intense light of an HPS system can cause a negative effect on these juvenile plants, stunting their growth or outright killing them. To counteract this, growers tend to keep the lights hoisted quite high away from the plants. However, the exact science of the right height gets difficult to determine. Too far away and the plants don’t grow enough, and too close the plants are killed.
There is a possible use case for HPS seedling phases in cold climates, due to the way they can act as a heater for the plants. However, basic climate control would be a more consistent choice. Plenty of growers have systems for this in place of course, but when starting with a new set up a lot of experimentation has to occur for proper growth to take place.
LEDs do a much better job during this stage of development, to the point that many die-hard HPS users have converted to LEDs for seedling growth. LED lights are much less intense, and can be adjusted further down to accommodate even the most delicate of juvenile seedling.
On every aspect of this stage, LEDs tend to win out when compared to high intensity lamps. It’s best to keep them put away until the next stages of growth, when plants can really begin to benefit from them.
Now HPS lights can come into play. During this stage of development, the plant can handle quite a bit more light, though heat should still be considered. This is when the plants stalk and stems start growing and the overall structure is created.
HPS systems are able to provide plenty of overall light to these developing plants, the results of which have been proven again and again since the first HPS indoor grows in the 70’s. MH may also be a good choice here as the blue light is good for vegetating plants, though that is another debate entirely.
The caveat to this is that the electrical costs of running these powerful lights for the length required, up to 18 hours a day, can be enormous.
LEDs, when run properly, are more than capable of providing enough light here, at a much lower cost as well. This is when the efficiency of LEDs really starts to help out, as where it lacks slightly in power compared to the massive gas tubes it makes up for in lower electrical costs.
The trade-off here is that LEDs require some fine tuning to ensure enough light is reaching the plants, this includes light spectrum adjustments and frequent height adjustments.
The argument between LED’s and HPS lights tends to come down to this final stage. Here a properly set up HPS lighting system can indeed outperform LED lighting, though the results can still be great in both cases.
The powerful red light produced by HPS systems mimics the end of summer and beginning of fall and brings plants to their flowering stage. They soak up red light readily now, and the power from a HPS has extraordinary results.
That heat is a problem though, as flowering plants can still be delicate when faced with the extreme temperatures produced by these almost fiery gas tubes.
LEDs, however, are capable of producing light in the red spectrum though the power of it is slightly diminished in comparison. It also offers the grower a way to slowly introduce the red spectrum to plants without having to change bulbs, which can be beneficial to avoid shocking them while also being budget friendly.
To get the largest harvest of plants possible, HPS tend to be the way to go here. However, LEDs perform almost just as well when aiming for a medium sized batch.
Outside of the idea of which light is better for growing big plants, there’s also the modern concern of climate damage and energy costs.
LEDs do a great job on growing plants without consuming a massive amount of electrical resources, and as the tech grows so too will the efficiency of them. LEDs are the only choice if consuming a large amount of electricity is a concern while growing, as HPS systems make a fairly large footprint when it comes to power resources.
There are a few factors to think about when determining exactly which lighting system will be ideal. A small enclosed area with little ventilation may get too hot when introduced to a HPS system, where LEDs may work just fine.
However, in an outdoor tent in a colder area the added heat from the HPS may be exactly what is needed to ensure a good crop.
A note should be taken about wattage. Though higher wattage lights, especially in an HPS system, will create more light, they will also create more heat. This means that the housing must be placed higher above the plant, creating a sort of diminishing returns scenario. Though more light is produced, it gets spread out more due to it being placed higher.
Taking account of the entire room, the amount of plants being grown, and figuring out exactly what is needed and not going overboard will help problems like this from appearing during a grow.
Growing with either type of these lights is perfectly viable. LEDs are the choice for those concerned about electrical bills and energy impact, while HPS lights are backed by decades of tradition and an understanding of all the variables growing indoors underneath them.
With all other things accounted for, efficiency is always the next best thing. In that way LEDs have helped this field grow and change in unprecedented ways by keeping the HPS old-guard on their toes and continuously adapting to the ever-expanding world of indoor growing.
Featured Image Credit: MARS HYDRO, Amazon
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