In her doctoral thesis, Letizia Monico, a researcher at Antwerp University and Perugia University showed that lamps which emit substantial amounts of light with wavelengths below 525nm (so green, blue and into UV) can damage paintings by some of the great masters. Details of her research and findings were published in Analytic
Chemistry with a corresponding press release here.
Vincent Van Gogh occasionally used a lead chromate-based yellow paint. Researchers discovered several years ago that the paint became darker over time. So Letizia Monico investigated the cause in her doctoral thesis. She and a group of researchers used x-rays to examine a series of Van Gogh paintings. Several of the yellows used in the paintings were found to be susceptible to darkening from exposure to green and blue light light and below on
the spectrum, especially those that were rich in sulfur. Van Gogh apparently used a lighter lemon-yellow and a lighter-still primula-yellow that were also very susceptible to darkening.
The researchers found that red light, which inherently has lower absorption energy than UV, UVA, or Blue light does not cause the chemical reaction that darkens the pigment. The researchers discovered the lead chromate-based yellow paint in a number of famous paintings including the ‘Portrait of Gauguin” and the ‘Sunflowers’. Monico advised that museums not use LED bulbs because they give off too much blue light.
Update: The LED industry has stepped up to contest Ms. Monico’s conclusion, citing that the study did not use LED lighting for its tests, but rather lamps with much higher blue and UV emissions that one would find in LED lighting (our follow on coverage here). The conclusion that LEDs would potentially cause similar issues would apparently be based upon the researcher’s impression of LED lighting being bluish, which as anyone familiar with the technology would know is an outdated view of “lowest cost” emitters that are generally not considered suitable for general lighting, much less specialized lighting as one would find in a museum setting.