Study On Lighting Spectrum Optimization Of Ancient Architectural Painted Cultural Relics Under The Coupling Impact Of Light And Humidity

In response to the call of"encouraging the opening of ancient buildings to the outside world"from the State Administration of cultural relics,the interior of the ancient architecture has been gradually open to the public,with the painted cultural relics on display.As the interior of ancient buildings is dark,which seriously affects the viewing effect,bringing a clear demand for lighting.However,there will be irreparable damage on precious cultural relics under lighting.Optimizing the spectral composition of light source can effectively reduce the light damage,and this technology is lacking at present.The fundamental reason is that the damage law of the spectrum to the painted cultural relics in ancient buildings is not clear.The spectral damage law of the painted cultural relics in museums obtained by our research group in the early stage is not applicable to these in ancient buildings,because the variation of temperature and humidity in natural conditions will affect the latter law.The lighting experiment under the coupling effect of light,temperature and humidity is an effective method to obtain the law of spectrum damage varying with temperature and humidity.However,due to the numerous experimental conditions,the experimental workload is heavy,and the theoretical research shows that the influence of humidity is stronger.Therefore,this study carried out the lighting experiment under the coupling impact of light and humidity to obtain the spectral damage law under the influence of humidity,fit the color-damage function,obtain the spectral response rate,and then optimize the spectrum,so as to provide technical support for the low-damage lighting of painted cultural relics in ancient architectural.The light aging experiment under the coupling impact of light and humidity was carried out,with 4 kinds of humidity（20%,40%,60%,80%）set as working condition,10 kinds of narrow-band LEDs as experimental light source and 19 kinds of pigments as experimental samples,which usually employed in painted cultural relics in ancient architectural.The total exposure was 12000Wh/m² for 11 irradiation cycles.The color data was measured in each cycle and calculated through the color difference method,and the color difference value was obtained to quantifiy the color damage to pigments.The color difference value of pigments was analyzed.Using the method of multiple linear regression,the color-damage function of humidity,exposure and spectral coupling affecting the pigments’color difference was established,and the four-dimensional image was drawn.The color-damage function described the damage law of pigment caused by humidity,exposure and spectrum,realized the calculation of color damage,and provided a basis for the mathematical expression of pigment spectral response characteristics under different humidity.Based on the color-damage function,the spectral damage law was normalized,in order to obtain the law that the relative spectral damage changes with the exposure.It is found that the spectral response rate of aging pigments tends to remain unchanged,which proves that the spectral response rate of painted cultural relics is not affected by the variable of exposure.The exposure variable was eliminated in the color-damage function,and the color damage of pigments caused by the rest variables（humidity and spectrum）was calculated,Then the spectral response function of pigment under different humidity was fitted.The spectral response function is a mathematical expression of the spectral response characteristics of pigments,which provides a basis for spectral optimization.Using the above spectral response rate function of pigments,the calculation formula for measuring the relative spectral damage degree of light sources was established.6¹⁰spectra were obtained with the 10 kinds of narrow-bands lights combined and superimposed.The color rendering index of all spectra was calculated,and 9477 spectra meeting the visual requirements were selected.By calculating the color damage degree of the above spectra with the formula,the optimal LED spectra with the minimum damage under different humidity conditions which met the visual requirements were obtained.In this study,the mathematical model of color damage to ancient architectural painted cultural relics caused by humidity,spectrum and exposure was obtained,with a four-dimensional visual expression of the law realized.The spectral response rate of painted cultural relics in ancient buildings under different humidity is obtained,and the mathematical description of spectral response characteristics of materials was realized.The minimum-damage spectra of ancient architectural painted cultural relics which met the visual requirements were obtained,which provided technical support for reducing lighting damage in ancient architecture and realizing protection and utilization of cultural relics.