White light-emitting diodes (LED) are well suited for museum lighting because they do not emit UV nor IR radiation, which damage artifacts. The color degradation of natural dyes and blue scale standards (JIS LO841) by white LED lamps are examined, and their performance for museum lighting is evaluated. Blue scale standard grades 1-6 and silk fabrics dyed with 22 types of natural dyes classified as mid to highly responsive in a CIE technical report (CIE157:2004), were exposed to five types of white LED lamps using different luminescence methods and color temperatures. Color differences were measured at each 15000 lx·hr (500 lx at fabric surface x 300 hr) interval ten times. Accumulated exposure totaled at 150000 lx·hr. The data on conventional white LED lamps and previously reported white fluorescence (W) and museum fluorescence (NU) lamps was evaluated. All the white LED lamps showed lower fading rates compared with a W lamp against Blue scale grade 1. The fading rate of natural dyes in total was equal between an NU lamp (3000 K) and a white LED lamp (2869 K). However, yellow natural dyes showed higher fading rates with the white LED lamp. This tendency is due to the high power characteristic of the LED lamp around 400-500 nm, which possibly contributes to the photo-fading action spectrum of the dyes. The most faded yellow dyes were
Ukon (
Curcuma longa L.) and
Kihada (
Phellodendron amurense Rupr.), and these are frequently used in historic artifacts such as kimono, wood-block prints, and scrolls. From a conservation point of view, we need to continue research on white LED lamps for use in museum lighting.
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