Cannabis cultivators find themselves in a dilemma called HPS (high pressure sodium) lighting versus LED (light emitting diode) lighting. On the one hand, HPS has been around in agriculture for a long time and has proven that it can successfully grow a wide variety of plants. On the other hand, LED, as the latest entrant to the horticultural lighting market is living up to its hype. What cannabis growers are concerned with are quick growth cycles of cannabis plants that yield many large flowers, containing high levels of THC (Δ-9-Tetrahydroannabinol), CBD, and other valuable secondary metabolites. Furthermore, growers need a lighting system that produces consistent results time after time as well as proven light recipes. Up to recently, no academic research had been done to compare the capabilities of these two lighting sources for growth of cannabis. Photo taken at MJardin, Denver, CO. Plant grown under the Valoya NS1 (sunlight) spectrum. An academic research titled ‘The Effect of Light Spectrum on Cannabis Sativa Morphology and Cannabinoid Content’ (G.Grassi, G.Magagnini, S.Kotiranta) has been presented at the Cannabinoid Conference in Cologne in September 2017 which presented a two-year long comparative study of HPS versus LED lighting for cannabis cultivation. The results show that the morphology of Cannabis sativa can be manipulated with light spectra. Plants under HPS treatment were taller and had more total biomass dry weight than treatments AP673L and NS1 (spectra by Valoya, the Finnish manufacturer of LED grow lights). HPS light spectrum is low in short wavelength irradiation (blue and UVA) and rich in green, yellow, red and IR in 800-1100 nm irradiation. This type of wavelength combination resulted in longer internodes and therefore taller plants with more stem dry weight. As for the compound accumulation in the flowers, treatments NS1 and AP673L had higher CBD and THC concentrations than HPS treatment. Treatment NS1 had the highest CBG Level. Spectrum NS1 is rich in short wavelength irradiation (blue and UVA) and had the highest R:FR ratio of all tested spectra. In addition to high cannabinoid content, spectrum NS1 enhanced the compact growth habit of the measured plants. The research suggests that the lower wavelengths, blue and UVA, could contribute to the higher cannabinoid yield in treatment NS1 compared to AP673L and HPS, respectively. In the rounds of the research the amount of THC produced under LEDs ranged from 26-38% more than compared to the HPS treatment. Three light sources were compared to each other. Spectra of the used light sources from left to right: HPS, AP673L and NS1. Plants under LED spectra were more compact and produced more cannabinoids than the HPS light source.