Lixi Liu et al 2017 Replacement policy of residential lighting for cost, energy, and greenhouse gas emissions Environ. Res. Lett. 12 114034
https://doi.org/10.1088/1748-9326/aa9447

Replacement policy of residential lighting for cost, energy, and greenhouse gas emissions

      In the U.S., lighting accounted for 280 billion kWh of electricity use or roughly 10% of the total consumption in 2015. Lighting upgrades are an easy way to cut energy use and therefore energy cost and GHG emissions. Upgrading the lighting infrastructure of the U.S. to LEDs in 2015 would have cut the annual energy use by 1/2, or up to 49 billion dollars in electricity costs. However, the high cost of solid-state lighting has slowed the transition. Many studies have used simple payback and other life cycle accounting methods to demonstrate the cost competitiveness and environmental benefits of LEDs, despite the high initial cost. However, since these studies do not consider the timing of replacement, they cannot determine whether a greater saving can be achieved from replacing an energy-inefficient lamp today or from waiting for the LED lamp to achieve a lower cost or a higher efficacy. The goal of this study is therefore to determine the optimal transition time to LEDs and provide specific replacement strategies for residential lighting.

      We developed an optimal replacement model for a 60W-eq light bulb, a common U.S. household lamp, using an approach that combines life cycle accounting methods with optimization techniques. 
This model considers various scenarios and conditions, including what type of lamp is currently in use, how the lamp technologies change, and how the electric grid decarbonizes.

      The study finds that all incandescent and halogen lamps should be replaced immediately with CFLs or LEDs. No replacement is advised for existing CFLs and LEDs. LED adoption is optimal today in terms of emissions. However, from an energy and cost perspective, LEDs should be adopted later with CFL use today because of improving efficacy and cost, which will provide greater life cycle savings. Lamps with high usage rates should be replaced first and frequently, because they benefit the most from efficacy gain. Replacing a lamp before it burns out seems wasteful, but this study shows potential savings in cost, energy, and emissions by replacing the lamp earlier than its rated lifetime. This is because of the rapid improvement of efficacy and cost, suggesting that efficacy improvement should be prioritized before durability in ongoing lighting research and development. The optimal replacement policy differs depending on the electric grid. For example, LEDs are adopted earlier and replaced more frequently in DC, California, and Hawaii, where the electric rates are high. Whereas from an emissions perspective, LED adoption is less urgent in California, where the carbon intensity of the grid is low.

      Informed buyers can use strategic replacement timing to maximize the economic, energy, and emissions benefits of lighting replacement. In general, replace all incandescent and halogen lamps immediately. And hold on to existing CFLs and LEDs for cost and energy savings. The model developed in this study can inform replacement strategies in other lighting sectors, including linear fixtures, high bay and low bay luminaires in commercial and industrial indoor spaces, which together represent over 60% of the potential market for LEDs.