This paper is fundamentally flawed because the authors chose to use an artificial 5 year horizon to compare a 10,000 hour operating life product with a 50,000 hour operating life product. The authors assume a 3,000 hour usage which by their own calculations gives the LED products a 16.7 year operating life. Using a 5 year time horizon for a product with a 16.7 year operating life is a fundamental error that would be obvious to any cost accounting or 1st year MBA student. This would be comparable to comparing the current cost of buying electricity from your electric utility to the 5 year cost of investing in solar modules on a KWH equivalent where the full cost of a 25 year solar system is amortized over 5 years -- the results would be just as meaningless and hopelessly biased against solar as the author's flawed analysis of HPS vs LED growing lights. Amortizing the costs of a 16.7 year operating life product over a five year time horizon invalidates the entire study.

The 3000 hour use case is imperfect. There are multiple use cases. The two primary ones are supplemental lighting and vertical farming. Supplemental lighting may only be needed for several months per year but is highly location dependent (e.g. a greenhouse in Alaska needs more than one in Hawaii). Vertical farming applications have much heavier duty cycles - 16-18 hours on average -- with more issues associated with heat given that many vertical farming applications stack multiple grow beds (Caliber Biotherapeutics in Byron Texas stacks 12 growbed layers with lights for each layer roughly covering 4'x4' sections). A better analysis would consider supplemental use over a wide variety of locations along with a vertical farming case.

The paper also ignores the effects of both historical and forecasted utility inflation. This is a significant variable for analyzing cost effectiveness of an energy efficiency investment with a 16.7 year life. Current EPA rulings on carbon dioxide emissions will force a significant percentage of existing coal plants to shut down between now and 2018 -- something that will significantly increase electric rates - particularly in areas like the South East that are heavily dependent on coal for their electricity. This analysis is region and utility specific so a proper analysis has to account for regional costs and inflation.

The paper ignores federal, state, and/or local incentives for energy efficiency that would reduce costs for LEDs. Every user (greenhouse or vertical farm operators) in the author's case scenario would qualify as ag producers for the 25% USDA REAP grant up to a total of $250,000. At a minimum, the authors overstated the cost of LEDs by 25%. There are many utility incentives that also apply -- many pay fixed amounts per fixture or a percentage amount (sometimes as high as 50% to 70% of cost). These would further reduce LED costs in selected markets - e.g. TVA, Bonneville Power Region, Baltimore Gas & Electric, etc. Hawaii and Oregon both have tax credit programs.

This paper should be withdrawn and updated.

For proper disclosure, I have an MBA and a PhD and provide due diligence and financial analysis on commodity investments in the agriculture, energy, and mining spaces as a partner at Chobe Advisers LLC. I have worked on and/or developed over 400 renewable energy and energy efficiency projects involving solar PV, solar thermal, biomass, fuel cells, energy storage, and LED lighting.