HPS Versus LED Lighting

When cultivating cannabis indoors, growers have no shortage of artificial lighting sources to choose from. However, the most popular options are high-pressure sodium (HPS) and light-emitting diode (LED) lights.

In this blog post, we discuss why these two are preferred over other artificial lights, the differences between them, and what to consider when choosing HPS or LED lighting.

Why use HPS or LED lighting over other options

The challenge with using any artificial light to replace natural sunlight is the energy cost, its wavelengths and the heat it emits.

With any artificial light fixture, the spectra are mainly linear lines, meaning that only part of the wavelengths can be absorbed by plants while the other wavelengths are wasted. Plants can only photosynthesize wavelengths within the photosynthetically active radiation (PAR) range of 400–700 nanometers (nm).

Creating light can also be quite energy consuming. Incandescent bulbs, fluorescent tubes, metal halide lamps and certain HPS lamps all require a lot of electricity, which can be cost prohibitive. They also produce a lot of heat, so they can’t be placed close to plants.

Table 1. Different light options available for horticulture, their wavelengths along the light spectrum and their lifespan, light intensity, and efficacy. Image source: Denver Department of Public Health. 2018. Cannabis Environmental Best Management Practices Guide. Scribd. https://www.scribd.com/document/433842238/Cannabis-BestManagementPracticesGuide-FINAL

HPS versus LEDs

HPS has been the primary lighting source in horticulture for decades, thanks to emitting adequate amounts of wavelengths in the PAR range, offering a low upfront cost and being energy efficient. HPS is considered a high-intensity discharge (HID) light and uses an electric current to excite xenon, mercury vapor and high-pressure sodium in the tube to create light.

LEDs are becoming just as popular as HPS, not only for their energy efficiency but also because of their wavelengths along the light spectrum. Using two semiconductors to create a spectrum of light, LEDs allow growers to provide wavelengths from the blue end to the red end of the spectrum (Figure 1).

Figure 1. The different LED light spectra based on the type of LED light used. Image source: Eichhorn Bilodeau, Samuel, Bo-Sen Wu, Anne-Sophie Rufyikiri, Sarah MacPherson, and Mark Lefsrud. 2019. “An Update on Plant Photobiology and Implications for Cannabis Production.” Frontiers in Plant Science 10:296. https://doi.org/10.3389/fpls.2019.00296

Most HPS wavelengths, on the other hand, only fall within the yellow and orange regions, with some red between 550–650 nm. While emitting a strong light at the red and orange end of the spectrum aligns well with the needs of flowering plants, HPS lights only emit around 5% of light within the blue range of 400–500 nm.[1] Blue and red wavelengths are both efficiently absorbed by primary plant pigments (chlorophylls), with red light the most energy efficient in LED production.

HPS lights also emit long-wave radiation (heat), which impacts leaf temperature, the cultivation climate and subsequently plant processes like transpiration and morphological development. LEDs, by contrast, emit very little heat.

Finally, LEDs offer a longer lifespan than HPS lights. LEDs last 25,000–50,000 hours[2]—potentially even up to 100,000—while the lifespan of an HPS lamp is around 10,000–20,000 hours.[3] LEDs also have a photoelectric conversion efficiency of around 50%, providing significant energy savings.

Table 2. An example of the differences in spectral wavelengths between an HPS lamp and two LED lights. Table source: Magagnini, Gianmaria, Gianpaolo Grassi, and Stiina Kotiranta. 2018. “The Effect of Light Spectrum on the Morphology and Cannabinoid Content of Cannabis sativa L.” Medical Cannabis and Cannabinoids 1 (1): 19-27. https://doi.org/10.1159/000489030/

Choosing between HPS and LED lights

HPS and LED lights both have their advantages, and research demonstrates that both are viable options for indoor cultivation. However, there are a few factors to consider that may help decide which is the better option.

Production size and setup

For large-scale operations with uniformly spaced plants, HPS is ideal because its light distribution is broader and more uniform over LEDs.

In high-density systems, LEDs may be a better option. High-density plantings may benefit from inter-lighting, a technique where light fixtures are placed closer to the plant so that light can reach the middle and lower canopies. Because of their low heat emission, LED lights can be placed within the plant canopy to increase light capture and cannabinoid yields.[4]

LEDs are also preferable for setups that require widely spaced benches due to their ability to efficiently focus photons on specific areas.[5]

Cost efficiency

One study conducted an economic analysis of common greenhouse lighting options, including LEDs, double-ended and mogul-based HPS lights, ceramic metal halide lights, and fluorescent light fixtures. The researchers found that the efficiency of the two most efficient LEDs and the double-ended HPS fixtures was essentially the same, ranging from 1.66 to 1.70 micromoles per joule (μmol J−1). The efficiency of mogul-based HPS fixtures, the most common type of HPS light, was only 1.02 μmol J−1.

However, despite the near-identical efficiency of both HPS and LED lights, the researchers found that LED fixtures cost five to ten times more than HPS fixtures over a five-year period due to the higher capital costs. When including electrical costs, LEDs are 2.3 times more expensive per mole of photons delivered than HPS lights.[6]

Cannabinoid concentrations

Using an HPS or LED light may also impact cannabinoid concentrations. One study found that THC percentages in C. sativa L. flowers were 9.5% under LED lights versus 15.4% for HPS lamps when their photosynthetic photon flux density (PPFD) was at 450, but concentrations of CBD and cannabigerol were higher under LEDs.[7]

Another study looked at a range of cannabis cultivars grown under LED and HPS lights and found that the percent of THC-A in cannabis flowers was 19.67% under HPS lights and 25.06% under LEDs (Figure 2).[8]

Figure 2. Potency means of 11 cultivars grown with HPS (ePapillion 1000w Double Ended bulbs) and LED (Fluence Bioengineering, now Fluence by Osram) (SPYDR xPLUS). Means with different letters are significantly different (T-test P <0.0001). Image source: See footnote 8.

Conclusion

Deciding which lighting source to use in indoor cannabis production depends on the growing setup, budget and desired level of control over spectral quality. HPS and LED lights both have their place in cannabis cultivation, so the choice should be based on each grower’s specific situation and goals.

Emerald Harvest Team

[1] Ouzounis, Theoharis, Eva Rosenqvist, and Carl-Otto Ottosen. 2015. “Spectral Effects of Artificial Light on Plant Physiology and Secondary Metabolism: A Review.” HortScience 50 (8): 1128-1135. https://doi.org/10.21273/HORTSCI.50.8.1128

[2] Sakinah Ahmad Rofaie, Nina, Seuk Wai Phoong, and Muzalwana Abdul Talib. 2022. “Light-Emitting Diode (LED) versus High-Pressure Sodium Vapour (HPSV) Efficiency: A Data Envelopement Analysis Approach with Undesirable Output.” Energies 15 (13): 4589. https://doi.org/10.3390/en15134589.

[3] See footnote 1.

[4] Viršilė, Akvilė, Margit Olle, and Pavelas Duchovskis. 2017. Light Emitting Diodes for Agriculture. Springer.  

[5] Nelson, Jacob A. and Bruce Bugbee. 2014. “Economic Analysis of Greenhouse Lighting: Light Emitting Diodes vs. High Intensity Discharge Fixtures.” PLoS ONE 9 (6): e99010. https://doi.org/10.1371/journal.pone.0099010

[6] Ibid.

[7] Eichhorn Bilodeau, Samuel, Bo-Sen Wu, Anne-Sophie Rufyikiri, Sarah MacPherson, and Mark Lefsrud. 2019. “An Update on Plant Photobiology and Implications for Cannabis Production.” Frontiers in Plant Science 10:296 https://doi.org/10.3389/fpls.2019.00296

[8] Jenkins, Michael W., and Curtis B. Livesay. 2021. “Photosynthetic Performance and Potency of Cannabis sativa L. Grown under LED and HPS Illumination.” Agricultural Sciences 12 (3): 293-304. https://doi.org/10.4236/as.2021.123019/

Share

Leave a comment

Your email address will not be published. Required fields are marked *

top