One Study concludes that “the most efficient HPS and LED fixtures have equal efficiencies, but the initial capital cost per photon delivered from LED fixtures is five to ten times higher than HPS fixtures.” Yes that’s right, they measured light by the photon; pretty intense right? Another interesting finding in the study is that light quality is much less important than light quantity. While light quality will govern certain aspects of plant metabolism, it has a small effect on photosynthesis which is the most important driving factor in plant development. While this goes against what many LED grow light manufacturers have to say about their products and the wavelengths they put out but, the fact remains that HPS lights are still the workhorse of the indoor cannabis industry, and for good reason. It wasn’t just any kind of HPS light that took the crown in that study: double-ended HPS fixtures were around 60% more efficient than the common mogul-base HPS fixtures.