Spectrally Enhanced Lighting--Field Evaluation Reveals Significant Energy Savings

November 17, 2006

A new report released by the U.S. Department of Energy documents field test evaluation results of spectrally enhanced lighting technology used in three buildings. Spectrally Enhanced Lighting is a lighting design technique that can save 20% more energy than commonly used T8/electronic ballasted fluorescent lighting systems.  Properly designed systems can achieve 50% savings over T12 and magnetically ballasted lighting systems. These savings are achieved by using naturally occurring visual efficiencies gained through the use of lighting whose color spectrum is more like daylight than most commonly used light sources, which are more yellow in appearance than Spectrally Enhanced Lighting.  The visual benefits from the enhanced spectrum include higher levels of brightness perception and visual acuity when measured at the same footcandle level.  These visual benefits were discovered during the 1990’s in US Department of Energy (DOE) research studies, which demonstrated these effects as a naturally occurring result of the eye’s response to shifting the color of light to include more blue in the spectrum.  

Shifting the color in fluorescent lamps to make a more Spectrally Enhanced light source is easily accomplished through mixing the phosphors of the lamps to achieve a higher Correlated Color Temperatures (CCT’s) and Color Rendering Index (CRI).  These shifts generally result in a higher Scotopic to Photopic ratio, or S/P value, which is used in the mathematical formulae to evaluate the visual effects.  For instance, a light source with a 5000K CCT and 82 CRI will have a higher S/P ratio than a 3500 CCT, 75 CRI fluorescent lamp, and will therefore provide better visual acuity under the conditions of equal measured lighting levels.  

Energy savings are obtained by using lamps that have a higher S/P ratio, and then determining the setting for the light levels that will result in equal visual acuity.  For instance, if the visual benefit from the enhanced spectrum is 20%, the lighting levels could be reduced by 20% to obtain the same reading ability, which therefore results in a 20% savings in energy.

Has Spectrally Enhanced Lighting been Tested in Real Buildings?

After the 2001 California brownouts, Pacific Gas & Electric Company (PG&E) decided to test the energy savings and occupant satisfaction of Spectrally Enhanced Lighting in real buildings.   PG&E retrofitted 7 of their own office buildings totaling approximately 300,000 square feet and found energy savings ranging from 30% to 65%, depending on the pre-retrofit lamp/ballast technologies.  In addition, there were not objections raised by building occupants to the change in lighting.

The informal findings from the PG&E buildings led to a DOE / PG&E jointly sponsored rigorous field study that compared two floors of an office building, one retrofit with 3500K, 82 CRI lamps and the other retrofit with 5000K, 82 CRI lamps with reduced lighting levels set to result in equal visual acuity.  The results of this study were that the energy savings were realized and there was no difference in occupant acceptance between the two floors.   This study provided abundant evidence for occupant acceptance and energy savings in a lighting retrofit application; however, the study was limited to two single floors within a building, making it too constrained to determine the economics of retrofitting an entire building with standard ballasts.  

With compelling evidence of energy savings and occupant acceptance in hand, the DOE performed a comprehensive field test in 2005 using three independent buildings that were entirely retrofitted with 5000K, 82 CRI lamps.  In this study, it was determined that energy savings of approximately 20% are obtainable for T8 to T8 retrofits and 50% for T12 to T8 retrofits.  The field study also concluded that there was no difference in occupant satisfaction between the old and new lighting, nor was there any increase in the use of task lighting as a result of the decrease in illumination levels. 

The studies described above were all performed as a logical progression to assess both energy savings and occupant satisfaction.  The cumulative and progressive results of these studies demonstrate that Spectrally Enhanced Lighting can provide significant energy savings without risk of occupant rejection or dissatisfaction.

Can I Use Spectrally Enhanced Lighting NOW?

The short answer is yes.  At this point, Spectrally Enhanced Lighting is a proven method for providing energy savings and there are no known negatives to installing this type of lighting in commercial office environments.   The 5000K, 82 CRI fluorescent lamp is manufactured by all the major lamp manufacturers and is easily obtainable, generally at no additional cost over lamps that have otherwise the same specifications for wattage, life, and lumen output.   

If you are considering performing a lighting retrofit or are designing for new construction, the payback is immediate since the energy savings are 20% better than alternative methods and there is no increase in installed costs.  When assessing a building that would otherwise not do anything, the payback on T12 systems is 1.4 years and the payback on existing T8 systems ranges from 3 to 4 years. 

For more details read the Spectrally Enhanced Lighting Program Implementation for Energy Savings Field Evaluation (PDF 4.1 MB) and Economics Validation Study (PDF 1.1 MB) .