基于光谱分析的彩绘文物照明光源损伤度评价方法

Evaluation Method for Damage Degree of Light Sources Used to Lighting Colorful Cultural Relics Based on Spectrum Analysis

光源中的光谱辐射是造成彩绘文物褪色、变色等颜色受损的重要原因,但不同光源的光谱功率分布不同,不同材料对各个波段光谱能量的吸收反射特性各异,导致在相同曝光量下对彩绘文物造成的色彩损伤程度有很大差别,特别是随着光谱构成灵活的LED(light emitting diode)在文物照明中的大量应用,如何对光源进行照明损伤度评价是目前亟待解决的关键问题。本研究在恒温恒湿条件下,以10种不同波段窄带光谱作为实验光源、以17种典型彩绘文物颜料作为实验样本开展累积1440 h的照射实验,以240 h为周期测量样本的CIE L^(*)a^(*)b^(*)色彩参数并转换为色差指标。绘制在10种窄带光谱照射下17种颜料的色差随曝光量变化曲线,基于曲线分析明确不同波段光谱对各类颜料的色彩损伤响应规律,并拟合得到颜料对光谱的响应函数,建立彩绘文物照明光源的光谱损伤度评价公式。研究结果表明:首先,无论在何种波段的光谱照射下,颜料平均色差随着曝光量的增加而增加,但增加幅度越来越小;其次,在相同曝光量下,波长越短的光源对颜料损伤越大,不同峰值波长对颜料色彩的影响比例为447 nm∶475 nm∶500 nm∶519 nm∶555 nm∶595 nm∶624 nm∶635 nm∶658 nm∶733 nm=1.000∶1.096∶0.816∶0.921∶0.853∶0.777∶0.814∶0.796∶0.706∶0.674;第三,基于光谱构成差异的光源损伤度评价公式为D=∫^(780)^(380)S(λ)〈0.468 exp{-[(λ-462.9)/17.75]^(2)}+0.6279 exp{-[(λ-535.1)/12.13]^(2)}+0.8135 exp{-[(λ-527.7)/463]^(2)}〉dλ,当使用光谱仪测得任意光源的相对光谱功率分布函数S(λ)后,将所测数据代入公式便可计算出待测光源的色彩损伤值D,成果可为彩绘文物照明中的光源选择和准入判定提供依据。

The spectral radiation in the light source is an essential cause of color damage,such as fading and discoloration of painted cultural relics.However,the spectral power distribution of different light sources is different,and the absorption and reflection characteristics of different materials to the radiation energy of each waveband are different,which leads to a great difference in the degree of damage caused to colorful cultural relics under the same exposure.Especially with the extensive application of LED with flexible spectral composition in cultural relic lighting,how to evaluate the lighting damage degree of the light source is the critical problem that needs to be solved.In this study,a 1440 hours experiment was used to irradiate 17 kinds of typical pigments of polychrome cultural relics with 10 kinds of narrow band spectrum under the constant temperature and humidity.By measuring the CIE L^(*)a^(*)b^(*)and calculating the color difference of pigments under different light sources every 240 hours,the curve of color difference changing with exposure was drawn.Based on the curve analysis,the change law and color damage response function of pigments to different wavebands is obtained,and the formula to evaluate the damage degree of lighting source on polychrome cultural relics is established.The results show that:firstly,no matter under any kind of narrow band spectrum,the average color difference of pigments increases with the increase of exposure,but the increased range is smaller and smaller;Secondly,under the same exposure,the shorter the wavelength,the greater the damage to the pigments.The influence ratio of different peak wavelengths to the pigments is 447 nm∶475 nm∶500 nm∶519 nm∶555 nm∶595 nm∶624 nm∶635 nm∶658 nm∶733 nm=1.000∶1.096∶0.816∶0.921∶0.853∶0.777∶0.814∶0.796∶0.706∶0.674;thirdly,the formula for damage evaluation of the light source based on the difference of spectrumisD=∫^(780)^(380)S(λ)〈0.468 exp{-[(λ-462.9)/17.75]^(2)}+0.6279 exp{-[(λ-535.1)/12.13]^(2)}+0.8135 exp{-[(λ-527.7)/463]^(2)}〉dλ,When the relative spectral power distribution function S(λ)of any light source is measured by the spectrometer,the color damage value D of the light source to be measured can be calculated by substituting the measured data into the formula.