With the prices of marijuana continuously going down, lowering the cost of production is becoming ever more critical. The highest costs associated with growing a pound of marijuana are canopy management, trimming, prepping/planting, and utilities. With LEDs, electricity costs for both lights and HVAC are 40% lower than with HPS lights. This is because HPS lights emit a lot of light and heat outside the plant-usable color spectrum (known as the PAR range).
I dislike HPS lights for other reasons too- they are too yellow, which makes the grow room visually uncomfortable, they emit UVA/B/C light (bad for your eyes), they burn at close to 1000°F (bad for whoever accidentally touches them), and bulbs need to be replaced every 6-12 months at $100 each.
I quit using HPS lights in 2015, and I have never looked back, but I have found that other growers, consultants and investors are still hesitant to follow suit. They usually cite concerns over whether or not LEDs are ready for prime time- whether or not they yield as well with great quality bud. They do, and these pictures prove it.
Besides the energy savings, the other major reason to use LEDs is because you can do vertical growing with at least two tiers under a 12' or greater ceiling. This doubles your canopy and yield in the same amount of floor space (and also costs a lot more to set up). The pictures above are a veganic sea of green (SOG) grow setup. Two vertical tiers can fit tightly into a room with an 10ft ceiling, although I advise my clients to have higher ceilings for the best possible air distribution.