#1. No Full Spectrum Control

The specific type of radiation plants need to begin photosynthesis, known as photosynthetically active radiation (PAR), is within the same range of light we can see. Plants consume all the colors (wavelengths of light) we perceive, from red to violet, and each color provides specific benefits to the plant. In nature, the colors the plants consume change with the seasons. As the earth spins around the sun, the angle at which sunlight hits the earth alters the ratio of colors, which cues plants to alter how they grow to prepare for the summer or the winter. These changes taken from sunlight’s cues are known as photomorphogenic responses.

In a grow room, in order to mimic sunlight, you need grow lights that produce the full range of PAR. You also need lights that can change the ratios at which the lights emit specific colors so you can get the plant to grow and flower as it would if it were outdoors.

HPS lights emit mostly red and yellow light, so to compensate, you may swap them out early in the cycle for Metal Halide, which emit mostly blue light, in order to trick the plants into their vegetative photomorphogenic responses. The process is very labor intensive, as someone must go to each individual light and swap out bulbs one by one, or set up an entirely different room for vegetative plant growth and later transport plants to a special flowering room. Also, neither bulb produces the full spectrum of light, so beneficial wavelengths of light, like green, are still left out. Green photons specifically are noted for their ability to penetrate canopies and shed more light deeper into the crop, but it’s often the most ignored wavelength in an HPS system. Increasing the photon diversity helps deliver more light to more of the plant.
Replacing HPS lights for full spectrum LEDs provides plants with a full range of PAR photons, which in turn, creates diversity within their cannabinoid and terpene profiles. By exposing the plant

 to more violet, orange, and yellow photons, it will activate more of the diverse range of photopigments to absorb the photons that chlorophyll can’t. These pigments, like flavonoids and carotenoids, add to the flavor and scent, and provide numerous beneficial effects.

#2. Too many parts

As you may know, an HPS system is not just a bunch of hanging light fixtures. It includes bulbs

hoods, ballasts, a duct system, and maybe even a carbon scrubber! Each feature is a new external element that has its own flaws. We call them pressure points. At every pressure point, there’s an opening for dust, debris, mold, moisture, bugs, and bacteria to latch on and build until they sabotage your crop. In order to compensate for these pressure points, these lights often need to be disassembled completely during cleaning, and then reassembled and rehung. The process is tedious, long, and not always effective.

Properly built LED lighting systems are self-contained. With no additional parts, there are no pressure points for hitchhiking bugs and bacteria to invade. In fact, an Ingress Protection rating for an LED light is a more accurate representation of its protection from the environment than the same rating for an HPS system, because the rating does not account for all of the external components of HPS lights. With an HPS light, you truly never know how safe you are.

#3. Too much heat

HPS lights emit a ton of heat. If you already operate an HPS system then you know that they can get incredibly hot. This extreme heat requires its own source of cooling, on top of the air conditioning needed to cool the ambient temperature of the room. The system for cooling these lights is often complex, and, if not properly cared for, can become a host to hitchhikers like dust, mold, moisture, and bacteria.

In addition to added complexity, the air conditioning needed to mitigate the extreme heat creates cold and hot zones on your canopy. A cold current will sweep through the bottom of the crop, while hot air rises to the top. When heat isn’t uniform throughout a crop, they grow poorly. The plant is performing reactions at vastly differing speeds from top to bottom, which impacts its shape and bounty by stressing the plant out. When heat is uniformly distributed on a crop, the plant becomes a finely tuned machine, with part and process operating in uniformity.

#4. Massive Infrared Spike

Sure, High Pressure Sodium grow lights can deliver abundant PAR to plants, but they also emit a ton of infrared radiation. In fact, roughly 30% of an HID light’s power goes into creating infrared radiation. This radiation is beamed directly onto the surface of the plant through radiative heat transfer, and raises the temperature of the leaves that it hits. 

In order for photosynthesis to work as efficiently as possible, leaf surface temperatures need to be within 85-88º Fahrenheit, the goldilocks zone for cannabis plants. At this temperature, RuBisCo, an enzyme within the plant’s chloroplasts, converts CO2 into sugar, starch, and other chemicals necessary for the plant to produce photosynthesis.

While photosynthesis occurs throughout the plant, the areas with the most photosynthesis producing chloroplasts are the leaves of the plant, so any rise in leaf surface temperature beyond the goldilocks zone will stress the plant, which results in the plant entering photorespiration. During photorespiration, RuBisCo accidentally grabs oxygen instead of carbon, and eventually burns more carbon than it absorbs.

That’s why it’s important to have lighting that doesn’t beam heat directly onto the surface of the plant! An LED light has no infrared spike, which helps the plant avoid stress and photorespiration.

#5. Height limit

Because of the immense heat emanating from HPS lights, cannabis crops grown under them have a built in height limit. If allowed to get too tall, the plants will be too close to the light, and cook under its heat. This results in a loss of trichomes and cannabinoids, lowering the quality of the crop until it eventually kills the plants. 

Because of the low heat of LED lights, plants can be grown taller and healthier, without feeling the stress of overheating. It’s the lack of heat that allows LEDs to be used not only horizontally, but also vertically. Hanging lights vertically in a multi-tier setup allows for grow space to be maximized, meaning crops can grow as tall as they want without ever running into an inhospitable heat zone.

#6. Low Efficiency

The main reason growers opt to get HPS over LED is because they think it will be cheaper. The initial cost for purchasing an HPS system is relatively low when compared to an LED system of similar power. What they may be surprised to learn though is that over time the cost of operating an HPS system will far outweigh the operation of an LED system, not only because of the added parts and replacements, but also due to the enormous amount of energy required to operate the lights. HPS systems are inefficient when compared with high performance LEDs that use the same power. This is due to the amazing efficiency benefits of LED, which converts more energy into PAR light than HPS ever could.

In fact, because HPS converts energy into only a sliver of the full spectrum of light, while also inadvertently creating a lot of infrared heat, the efficiency of HPS systems is often drastically lower than LED. To compete with the light intensity output of an LED light of the same class, HPS lights must be run at higher power, which exhausts bulbs, and raises expense.

SEE HOW LEGION OF BLOOM BECOME A MORE EFFICIENT FACILITY WITH FOHSE LEDS:

#7. Labor intensive

Within every shortcoming of HPS there is the added cost of labor. Because its inefficiency exhausts the bulbs, the bulbs need to be replaced. Since its spectral output is limited, the bulbs need to be replaced. To ward off pests and harmful hitchhikers, its multiple parts need to be disassembled, cleaned, reassembled and mounted. Each task is an added cost as it requires someone to go to each light, one at a time, and tend to the lights. Seeing as it’s already costing you to not only run the light, and keep it cool while keeping the ambient temperature around it low, the added stress of now having to maintain a fleet of lights can break the bank for a lot of growers, big and small. 

HPS lighting was instrumental in the early days of indoor cannabis cultivation, but as the world has improved its view of cannabis use, so too has the technology improved around it. There are easier ways to grow cannabis that produce not only healthier, richer crops, but do so for less energy, time, and money. 

The question isn’t whether you can afford to switch to LED, but rather, if you can afford not to. Click below now, and request your free light plan.