@georgesplane- I watched a few LED grow light video reviews and the LED lights outperformed the HPS lights every time. The reviews used light set-ups of equivalent wattage with very similar square footage and plants. The yield on the LED set-up was about 40% better than the yield of the HPS set-up under similar conditions.
I do not know what the price difference is, or which product lasts longer, but as far as energy use is concerned, the LEDs are better. You should weigh the energy savings against the costs of purchasing and maintaining the two types of systems before making your purchase. This will give you the full operating costs of the two technologies.