From the PACCIN listserve

"Preservation of Light Sensitive Materials"

From:"Rosenfeld, Scott"

“Generally avoid picking higher color temperature lamps for light sensitive materials as these as these LED’s have an unacceptably large peak in the ‘blue region’ of the spectrum.“ This is the take-away from the report that Dale Konkright mentioned, “Guidelines for Selecting Solid State Lighting for Museums” by Jim Druzik and Stephan W. Michalski (June 2011). The intention of this report was to champion the use of quality LED’s in museums, especially warm LED’s <3500K, not to slow their adoption.

The CIE report on Optical Damage (CIE 157:2004) is the internationally agreed upon standard for how to evaluate the damage factor and choose the right lighting source for a collection of materials. The same criteria is used to evaluate the spectrum of any lighting source: LED’s, incandescent, daylight, HID or fluorescent. There are three factors that determine the damage potential of any lighting source: the quantity of irradiance, the duration of exposure and the spectral composition.
The recent discussion on LED’s has focused on the spectral component. While museums need to get better at evaluating the spectrum of our sources; the most important detail is still limiting illuminance and the duration of exposure (the first two factors). For example the CIE report indicates that daylight at 6000K is twice as damaging as incandescent at 2850K. This doesn’t mean that museums shouldn’t use daylight on their oil paintings. It is important to remember, “We have to accept a certain amount of damage caused by the very act of display” (Thompson, 1986). Lighting standards are chosen for what humans need to appreciate artwork, although that quantity of light still causes damage. So while 150 lux of daylight may be twice as damaging as 150 lux incandescent, 150 lux is still the amount of light that we need to see an oil painting at an optimal level. Highly light sensitive materials need to be treated with more care and kept away from high Kelvin temperature sources like daylight (IESNA RP-30-96).
The best advice is standard museum practice: Evaluate collections as highly sensitive to light (50-75 lux) or low sensitive to light (200 lux) and then stick to those lighting levels and control the duration of exposure. In my opinion the best new lighting technology to both save energy and preserve light sensitive material is the occupancy sensor that dims the lighting when the objects are not being viewed. LED’s are also a wonderful new tool and I’ve started using retrofit lamps in my collection, thankfully with the Getty conservation lab’s blessing.
For more information: CCI has a wonderful website that provides information on the preservation of light sensitive materials at http://www.cci-icc.gc.ca/crc/article...hap08-eng.aspx. I am chairing an IESNA committee to revise RP-30; the current manual was written in 1996 but is still very informative. It can be purchased at http://webstore.ansi.org/RecordDetai...IESNA+RP-30-96. Lastly; AIC’s Green Resources page has extensive information on LED’s. http://www.conservation-us.org/index...ge&PageID=1212


Scott Rosenfeld, LC, IESNA
Smithsonian American Art Museum