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Comparing LED vs HPS Lights

Jun 1, 2020
Types of Lights

Lighting Systems for Cannabis Grow Areas

High-pressure sodium (HPS) lights have been a leader in the indoor gardening world for decades. Other lighting systems fail to compete with them, thanks to their numerous benefits. What makes these lights so popular, and what other options remain available to cannabis growers?

Indoor Marijuana Cultivation

Many cannabis enthusiasts and home growers choose to cultivate indoor cannabis seeds rather than the outdoor variety. When doing so, they retain full control over all aspects of the growing process, including the humidity, temperature, and grow medium. Furthermore, indoor cultivation allows for year-round growing and a larger yield.

Lighting becomes of great importance when growing marijuana indoors. Cannabis farmers must ensure they provide the lighting needed for plants to develop and thrive. They need to recreate the spectrum of natural light, and the lighting industry recognized this. It responded, and individuals find products today designed for any lighting scenario, including lights providing different spectrums and colors – many of which are fully adjustable.

Knowing the difference between the different types of lighting becomes of great importance when choosing how to spend your own money on new equipment. Cannabis farmers likewise must know the various applications for each lighting option. Different times call for different spectrums, and growers need to remember this, as different configurations can affect the overall yield.

Lighting Options

Before purchasing any lighting system, growers must understand the similarities and differences among the various options. LED lights have been around for years, but growers should not limit themselves to this particular option. Other options might provide a better fit for your growing needs.

HPS Lights

High-pressure sodium or HPS lights emit light by sending an electrical current through a pressurized quartz tube that contains a sodium and mercury vapor gas mixture and the inert gas xenon. When these gases heat up, light is emitted.

The sodium found in the mixture produces a yellow-orange light that is very intense. When the sodium combines with the mercury and xenon a white light appears because the mercury and xenon both emit light found in the blue end of the visible spectrum.

LED Lights

In contrast, LED or light-emitting diode lights serve as semiconductors and are made up of two different materials, one with a positive charge and the other with a negative one. When the voltage reaches the LED, an electric current starts to flow through the light, causing the opposing charges to collide. During this collision, energy is released and the light appears.

Initially, LED lights offered low light output, and users only had a few colors to select from. Today, LED lights come in numerous colors in the ultraviolet, infrared, and visible spectral ranges.


Determining the efficacy or luminous efficiency of a lighting system requires the use of a basic equation. Take the lumens or output of the lighting system and divide this number by the watts or total power of consumption. To qualify as high-efficiency lighting, the system needs an output of 90 lumens per Watt  (lm/W) or higher. Today, some bulbs provide 150 lm/W or more, so compare numerous options before making a purchase. Certain grow light manufacturers use a different system for rating their products. They measure photosynthetically active radiation (PAR) output or the number of photons per second falling on 1㎡ of plant matter or µmol/s.

High-performing HPS bulbs provide approximately 150 lm/W. Two of the best available today produce 90,000 lumens and 92,000 lumens over the first 100 hours of use. Newer lights of this type include the PAR output rating as well.

When purchasing LED grow lights, look at the PAR output, as this provides more information than lm/W. Red-blue light systems feature a significantly lower lm/W ratio overall. These lights provide only those light bands required for photosynthesis. As a result, the lights eliminate the expenditure of unnecessary energy.

Nevertheless, new lights of this type rely on multiple bands to provide a spectrum of light that is more complex and full. Growers believe this benefits plant growth, so more manufacturers include white in the visible spectrum alongside purples and reds. When purchasing one of these lights, look for both the lm/W and PAR rating, as reputable manufacturers typically include both.

Imitating Daylight

HPS lighting systems fail to replicate daylight as well as their modern lighting counterparts. Sodium vapor provides a light that is distinctly reddish-yellow when mercury and xenon aren’t added in. Fortunately, manufacturers recognized this could become a problem and created full-spectrum HPS bulbs.

Full-spectrum HPS bulbs incorporate a metal halide component with the HPS element. This combination provides a more accurate representation of natural daylight than HPS bulbs alone.

LED bulbs, on the other hand, come in full-spectrum models. Growers find their plants receive exposure to as many as 11 bands of light wavelengths. These bands range from infrared to ultraviolet.


Plants need light and water to grow and thrive. As a result, lighting plays a critical role in terms of the final yield. Annual flowering cannabis strains adhere to very strict patterns with regard to day and light hours, the light spectrum, and temperature.

The light spectrum changes as the seasons change, and the same holds true for other factors that impact the flowering of all sativa and indica marijuana plants. To obtain maximum yields, growers must expose the annual flowering plants to different lights at various parts of the growth cycle. Autoflowering strains are the easiest type of marijuana to grow in many ways, including the fact they can flower in any amount of daylight hours each day (generally the more the better).

Growers rely on HPS lighting during the flowering stage of the growth cycle because the spectrum of light emitted encourages the production of flowers. LED lighting benefits plants at this stage as well, thanks to the lumens produced by these bulbs. Most annual species flower during the summer months, as that is when sunlight abounds.

Experienced growers use fewer lights early in the grow cycle to protect seedlings and young plants from excessive heat and light. Either or both damage tender plants. As the cultivation process moves forward, increase the number of light globes. This ensures your gelato og or tangie plants receive enough light as they get bigger.


Consider the environment when selecting grow lights. The lighting used in an indoor grow area impacts the temperature in this space, so men and women must take this into account before buying a lighting system or bulbs. Many growers find it difficult to regulate the temperature in their grow space and spend a fortune cooling the area when the wrong lights are selected.

HPS lights generate a significant amount of heat. While these lamps are 30 percent more efficient than incandescent lamps, a large portion of the power going to the HDS lamp is lost to heat. Cannabis farmers in warm climates and those who cultivate crops during the summer must account for this heat loss, as a hot environment harms the plant and dries it out quickly. When using HPS lamps, growers must water their cheese fem or big bud strain plants more frequently and ensure the temperature remains at the desired level. However, farmers in cold climates benefit from the purchase of these lamps, as they save time and money by increasing the temperature in the grow room.

LED lights lose very little energy to heat, making them more efficient than their HPS counterparts. In fact, they are 80 percent more efficient than incandescent bulbs. The LED driver generates the heat in these bulbs, meaning the light emits minimal heat. Growers receive the option of only cooling the driver to save money. However, heating costs increase in the winter when the entire greenhouse requires heating for plant protection from the cold.

Growers frequently chose their system based on the initial cost and ongoing maintenance. Energy costs differ significantly between the two systems, as LED systems are 70 percent more efficient. Run five LED grow lights at 165 watts for 12 hours each day and spend $371 at $0.12 per kilowatt hour. Replace the LED lights with 400-watt HID fixtures, which are the equivalent of the 165-watt LED bulbs, and the cost increases to approximately $900.

LED lights last longer as well, as they run on average 50,000 hours before they dim. Nevertheless, HPS lamps cost less at the time of purchase and come in modules. Replacing a module rather than the entire system keeps costs down. LED grow lamps come with few replaceable parts, while HPS lamps, hoods, and ballasts can be changed out. In addition, extending the lifespan of an HPS lamp becomes easy with proper bulb and ballast care.

Electricity Costs

Operating grow lamps costs money. Consider electricity rates in your area when comparing lights as well. North American growers pay less for this service and often use 1000W bulbs. In contrast, European growers frequently use 400W or 600W bulbs as they cost less to run in an area with high electricity rates.

One option for saving money involves using fluorescent lights in the early phases of plant growth. Young plants and seedlings require little light when compared to mature plants, so fluorescent lights tend to be enough. Other growers choose to use fewer lights with seedlings and young plants, adding more lights as the plants grow.

Combining different light systems creates more complexity in the grow room. As a result, mistakes become more likely as there are more variables to control. Keep this in mind when selecting lighting systems for your grow area. Those wanting minimal maintenance and upkeep need one lighting system. As the grower obtains more experience and knowledge, more systems can be purchased.

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