Spectral Optimization On LED Illuminating Chinese Fragile Cultural Relics Based On Color Rendering And Color Protection

Lighting environment,as an important part of the museum’s overall environment,is the most special and complex in museum compared with that of other types of buildings such as office,classroom and commercial buildings.General building lighting only needs to meet the basic use requirements of personnel,while museum lighting needs to ensure the light safety of cultural relics besides the ornamental requirements of personnel.It has dual attributes of visual comfort(human needs)and light protection(cultural relics needs),which should be met simultaneously.Chinese fragile cultural relics,such as calligraphy,painting and ancient books,are the highest light-sensitive exhibits stipulated by the International Commission on Illumination(CIE).They have a high vulnerability and are also the key types of research.The spectral composition of the light sources for cultural relics is the key to determine the display and protection effect,but there are problems to be solved at present:in the ornamental field,CRI,CQS,TM-30 and other color rendering evaluation standards adopted internationally are mainly for general lighting scenes,and they are not suitable for the special light environment of museums which characterized by low illumination,low color temperature and high contrast.The color samples used for evaluation deviates seriously from the color of the fragile cultural relics in China with poly chrome,medium brightness and low saturation.Therefore,there is a big error between the evaluation results and the real color perception when the current results are used to evaluate the color rendering of the light sources illuminating fragile cultural relics in China.In terms of protection,the color fading,discoloration and color disappearance of cultural relics are caused by the photochemical reaction of the pigments after absorbing the energy of light sources.But there are many kinds of materials of fragile cultural relics pigments in China,and the spectral differences of various light sources are enormous.Therefore,the photochemical reaction process under the condition of a multi-parameter combination is very complex.At present,the rule of color damage to various pigments by different spectral composition has not been clarified.Aiming at solving the above problems in ornamental and protective aspects:Firstly,based on the analysis of the existing research system and methods of colorimetry,the visual color difference of Chinese fragile cultural relics under different light source spectra was obtained by cyclic colorimetric experiment.According to the experimental results,the elements in the evaluation system of color rendering were optimized,and the suitable evaluation method of color rendering was put forward.Secondly,based on the characteristic that LED can adjust the spectrum composition according to the need of use,450 nm,510 nm,583 nm,650 nm monochrome lights which constitute the spectrum of four-primary LED were used as the experimental light source,and Chinese vulnerable cultural relics pigments were used as experimental object to carry out long-period irradiation experiments.Through the analysis of the experimental results,relative damage coefficients of monochromatic lights to various pigments were got,and a formula for judging the color damage degree of fragile cultural relics in China was proposed.Third,by calculating the color rendering of all spectra through the proposed"light source color rendering evaluation formula",the spectra that dissatisfy the requirements of color rendering were removed;and by using the proposed formula for determining the color damage degree of cultural relics,the residual spectra that meets the requirements of color rendering were calculated,and the lowest damage spectra in the color temperature range of 2700K-4000 were screened out.Research results clarify the influence of different spectral compositions on the color rendering performance of light sources and the color damage of cultural relics.On the basis of solving the above scientific problems,two practical techniques,namely,the evaluation method of the color rendering performance of light sources and the determination method of the color damage degree,were put forward.Minimum damage LED spectral database meeting the color rendering standard and aiming at different cultural relics materials was established to illuminate fragile cultural relics in China.The achievements provide a scientific basis for the development of minimum damage LED light source.