Optimal LED spectrum for lighting Chinese paper cultural relics in museums

In museum lighting, Chinese paper cultural relics are prone to cracking, embrittlement and other photochemical damage after absorbing the spectral energy of light sources. Owing to the different absorption and reflection characteristics of paper for different bands, optimizing the spectrum compositions of light sources can provide effective protection, the basis of which is to clarify the influence rule of spectra on the paper. However, the methods of color difference and Raman spectroscopy, which are widely used in the current research, cannot scientifically measure the lighting damage. In this study, Fourier transform infrared spectroscopy was used as the evaluation method, and 10 kinds of narrow-band lights were used as the experimental light source to conduct a 1440 h irradiation experiment on the samples of the ancient Chinese Xuan paper. The oxidation index was calculated as the evaluation index based on the infrared spectra measured every 240 hours, and a mathematical model for the response rate of paper to spectrum and exposure was established. 610 spectra were obtained with the 10 kinds of narrow-band lights combined and superimposed. The color rendering indexes of the above spectra were calculated, and 9,477 spectra that meet the requirements of viewing indicators were obtained. By calculating the damage degree of the above spectra with the model, the optimal LED spectrum with the minimum damage which met the visual requirements was obtained. Then it was input into the 10-channel spectral simulation system for spectral restoration. Two kinds of lights commonly used in lighting for paper cultural relics were selected to conduct a comparative experiment. The results showed that the optimal LED spectrum reduced damage degree by 49.4% and 59.7% respectively compared with the two kinds of contrast light sources, and was beneficial to energy saving.