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U.S. Department of Energy Energy Efficiency and Renewable Energy

Potential Payback for Spectrally Enhanced Lighting

For businesses, the payback time for spectrally enhanced lighting (SEL) is key. This page discusses energy savings and payback periods after implementing SEL.

The following potential payback scenario is based on a building tenant with 50,000 sq. ft. of open office space with 2x4-foot lensed luminaires on 8x10-foot spacings (total 625 luminaires). Each luminaire has three 735 T8 lamps and a 3-lamp, normal (0.87) ballast factor electronic ballast. The lighting system was installed in the mid-1990s. The ballast data shows that each luminaire consumes 90 watts, so the total wattage for the lighting system is 56,250 watts. The system is on for an average 12 hours per day, five days a week plus some weekend hours, for a total assumed 3,500 annual hours of use. The annual energy consumed by the lighting system is therefore 197,000 kWh.

The 850 spectrally enhanced lighting allows the design team to reduce the lumens per luminaire by 32% and obtain the same visual ability. For the purposes of this illustration, the team will de-lamp the luminaire to two lamps and change the ballast to extra-efficient instant-start electronic ballasts with the same ballast factor (.87) to achieve this one-third reduction. The new wattage of the lighting system is now 53 watts per luminaire at a cost of $40.00 each.

Energy Savings and Payback Calculation Results

The cost to change the lighting system is $25,000 and the annual energy savings are 81,000 kWh. The annual energy cost savings will depend on the utility rates, which are shown in the chart below. For more information, please see Spectrally Enhanced Lighting Program Implementation for Energy Savings: Economics Validation Study (PDF 1.2 MB). Download Adobe Reader.

Image of a bar chart entitled 'Spectrally Enhanced Lighting Simple Payback.' The y-axis shows payback in years. The x-axis shows electricity rates in $/kWh. The graph indicates, for the example provided in the text, a roughly 7.5 year payback period when electricity rates are $.04/kWh. The payback period steadily declines until the last bar showing a one-year payback when electricity rates are $.26/kWh.

Spectrally Enhanced Lighting Simple Payback


The calculations in the table above do not include the additional potential for reduced cooling costs resulting from lowered heat generation by the new lighting system. In addition, the new lamps have longer life spans, and will provide additional savings over the life of the system by lowering the maintenance costs of lamp replacement. The benefits of installing new ballasts are also significant, since the existing ballasts are approximately 10 years old and approaching the end of their life. The new system life will be approximately 15 years, and based on the life of the new lamps (24,000 hours), the lamps will require changing only twice over the life of the system.

The energy savings from this approach result in a one to three year payback for regions where the electric utility rates are $0.10 per kWh or higher. At least 80% of these savings are attributable to SEL, with the remainder attributable to the use of higher efficiency electronic ballasts. These energy savings are also permanent load reductions; those paybacks would be better in areas where peak demand charges are even higher than those used in this example.