The US Department of Energy (DOE) has released another Gateway report detailing a solid-state lighting (SSL) evaluation and documenting favorable results in using LEDs to light three galleries in the J. Paul Getty Museum located in Malibu, California near Los Angeles. The project involved a retrofit of track lighting – replacing 60W PAR38 halogen lamps with 12W LED-based lamps – to deliver energy and maintenance savings
The LED evaluation was conducted by the DOE's Pacific Northwest National Laboratory in collaboration with the Getty Conservation Institute (GCI). The team projected a 10-year, life-cycle cost analysis of the LED lamps that yielded present-value energy savings of $4621 and total savings of $9843 including maintenance. Based on an electrical rate of $0.12/kWh, the simple payback is projected at 2.3 years.
The Gateway test, however, attempted to do more than measure energy and maintenance savings. The team wanted to study the potential damage caused by light on valuable artifacts and specifically the impact of LED lighting relative to legacy halogen sources.
Lighting old photos
Over the course of more than six months in 2011, the Getty museum hosted a special exhibit entitled "In Search of Biblical Lands: From Jerusalem to Jordan in Nineteenth-Century Photography." The pieces were produced between 1840 and the early 1900s and included salted-paper prints, daguerreotypes, and albumen silver prints.
Jim Druzik, senior scientist at the GCI, led the tests and had previously concluded that LEDs wouldn't cause more harm than halogen lamps, which would have typically been used to light the photographs. Still, Druzik planned to test the LED lights by collecting in-situ color measurements every two weeks from three of the exhibited photographs, hoping to detect color changes or fading. The goal of the team was collecting data that would allow it to predict in advance when lighting might cause a detectable change in a photo.
The tests used a Cree PAR38 LED lamp that has a 20° beam angle compared to a 30° beam angle for the halogen incumbents. The LED lamps had greater center-beam candlepower, but lower total lumen output. With either lamp the museum must use screens in front of the bulbs to reduce light output to the prescribed 50-lx level.
At the end of display, the GCI team fitted the measured color data to a mathematical model that projected color changes measured in CIEDE2000 (a CIE standard for measuring color difference) units. The result was a projection of a 1.5 CIEDE2000 shift over a 110-week exposure to the LED source. The 1.5 unit difference is the level that is called a just notable difference.
The Gateway report doesn't quantify the color shift as favorable or unfavorable but simply states that curators must monitor and control the exposure of art to light to meet preservation targets. The deterioration was judged no worse than what filtered-halogen sources cause with similar lux-hour exposure.
The report did note that LEDs may offer an advantage going forward in that SSL technology can allow for a tunable spectral power distribution that could eliminate short wavelengths in the visible spectrum that are known to damage art. Of course LEDs can be specified to avoid the damaging UV and IR bands, while that requires the use of the aforementioned filter for halogen sources.
The museum did not attempt to gauge the opinion of the viewing public on the quality of the LED light. The fact that LED lights were used in the presentation was not revealed in any way.
Department heads at the Getty did tour the exhibit and judged the LED light favorably. The project team also noted that there was no lamp failure and no detected color shift in the lamps during the course of the exhibit.