Spectrally Enhanced Lighting

Photo showing the ceiling of an office. The left side of the ceiling shows a row of fluorescent troffer lighting, and the right side of the ceiling shows spectrally enhanced troffer lighting.width=

This photo compares warm-colored fluorescent lamps (left) that have a correlated color temperature (CCT) of 3500 kelvin (K) and color rendering index (CRI) of 75 with the whiter and more natural appearing SEL (right), which has a CCT of 5000K and CRI of 82. The energy-saving SEL lighting system provides the same or better vision than the lamps on the left, even though the light output of SEL lighting is lower.

Major SEL Research

1987: After an independent study found that high-pressure sodium lighting deficient in blue-colored wavelengths resulted in poorer vision relative to incandescent lighting, DOE research determined that spectrum affects the eyes pupil size.

1990s: DOE studies concluded that lighting at higher correlated color temperatures provides better visual acuity than warm-colored sources.

2004 and 2006: DOE sponsored two field studies on the practical application of the SEL method (see Resources).

2010: A definitive study on visual acuity and spectrum demonstrated how spectrum affects low-contrast tasks in typical interior lighting applications.

Spectrally enhanced lighting (SEL) is a cost-effective, low-risk design method for achieving significant energy savings. It entails shifting the color of lamps from the warmer to the cooler (whiter) end of the color spectrum, more closely matching daylight. Studies show that, with this color shift, occupants perceive lighting to be brighter and they are able to see more clearly. Since SEL provides the same levels of visual acuity with fewer lumens of output, SEL installations can be designed using fewer lamps or lower wattage lamps than traditional lighting.

While the principles of SEL are applicable to any light source, it is predominantly used for fluorescent lighting applications in commercial and industrial settings. The examples and implementation guidance provided here pertain to fluorescent lighting.

The feasibility and economic benefits of SEL have been extensively studied, and case studies have documented the approach and savings realized in both new construction and retrofit applications (see Resources below).

Energy savings from SEL—which depend on the existing lighting in the candidate space (or the proposed lighting for new construction) and the illumination requirements—are generally in the range of 20% to 40%. SEL installations typically use high performance fluorescent lamps with a correlated color temperature (CCT) of 5000K, in contrast to conventional fluorescent installations with CCT in the range of 3500K. Savings can be optimized by installing lower-ballast-factor, extra-efficient electronic ballasts along with the higher CCT lamps.

In 2013, the Illuminating Engineering Society of North America (IES) published a Technical Memorandum that investigated the many facets of how spectrum affects vision. IES TM-24-13 concludes that light source spectral power distribution can be factored into lighting calculations for visually demanding tasks within IES Illuminance Categories P through Y. This publication allows the use of SEL for interior lighting applications such as offices, libraries and schools, medical and laboratory facilities, and manufacturing and inspection applications.

Resources

The energy-saving benefits of SEL have been extensively documented. The science that linked spectrum to vision was funded by the Department of Energy at Lawrence Berkeley National Laboratory between 1986 and 2000. A feasibility study and an economic validation study funded by the Department of Energy found energy savings of between 19% and 46% for various field installations, with no measured difference in occupant satisfaction and no increase in the use of task lighting. Visual acuity benefits and occupant acceptance of SEL lighting have been independently corroborated by research outside the Department of Energy.

SEL has been used successfully in new construction and retrofits, as exemplified in the following case studies:

Download Implementing Spectrally Enhanced Lighting for guidelines on applying SEL, including a method for calculating the reduction in light levels with SEL and examples of energy savings and paybacks under different scenarios.