Payback is summarized in Figures 1 through 4, each of which shows all four electricity rates for one combination of operating hours and installation time. Total present-value life-cycle costs —after 10 years of use at the specified hours of use per year, and with the specified installation time—are graphed versus the LED equipment cost per two-lamp troffer. The savings or added costs incurred from using LEDs versus the benchmark fluorescent, which has a fixed equipment cost of $30, are shown in relation to the cost of electricity. That is, each chart shows what combination of electricity rate and equipment cost is needed for economic viability of the LEDs, at the given hours of use and installation time.