Abstract:As an important part of the exhibition environment of the museum, the lighting of exhibits directly affects the protection of cultural relics in the museum and the visual experience of the audience. The design should be based on the basic principle of protecting the exhibits and facilitating the viewing of the exhibits. According to the sensitivity of the exhibits to light and the requirements of the exhibition design, the illuminance value and color temperature are reasonably set, effective technical measures are taken to limit the annual exposure of the exhibits, and on the basis of comprehensive consideration of the color temperature, luminous efficiency, color rendering index, ultraviolet and infrared content, service life and other parameters of the lighting source, the lighting source with good performance is selected, and the original appearance of the cultural relics is truly presented for the audience under the premise of avoiding the damage of optical radiation to the cultural relics, and their historicity and artistry are better displayed. So that the audience can fully feel the cultural connotation contained in the exhibits.
Cultural relics carry a splendid civilization and are a precious historical and cultural heritage of mankind. Since the "13th Five-Year Plan", the mainland's cultural relics industry has entered a period of rapid development, and the number of cultural relics in the national museum collection has increased from 41.392 million pieces (sets) to 51.274 million pieces (sets), an increase of nearly a quarter. It is the duty and mission of cultural relics workers to protect and inherit these irreplaceable and non-renewable precious historical and cultural relics. The study shows that the environmental factors affecting the preservation of cultural relics mainly include temperature and humidity, optical radiation, air pollution, insect and microbial reproduction, etc. Among them, optical radiation can cause irreversible damage to cultural relics of organic matter. However, in museum exhibitions, lighting is an indispensable and important means of displaying cultural relics, and its design level directly affects the protection of museum cultural relics and the visual experience of the audience, which is an important topic worthy of study for museum practitioners.
Lighting refers to the use of artificial light as a light source to illuminate a place or object. Reasonable lighting settings have the characteristics of easy light control, strong stability, flexible light distribution, etc., which are more conducive to showing the details of cultural relics and presenting the history and artistry of cultural relics to the audience, which is an important form of expression for the creation of the exhibition environment atmosphere of the museum. However, artificial lighting consumes a large amount of energy, and most of the lighting sources contain ultraviolet or infrared rays to varying degrees, and the optical radiation generated will cause damage to cultural relics. Therefore, the key part of museum exhibition lighting is the lighting of exhibits. Its design should be based on the basic principle of protecting the exhibits and facilitating the audience's appreciation of the exhibits; According to the sensitivity of the exhibits to light and the requirements of the exhibition design, the illumination value and color temperature of the exhibits, the limit of the annual exposure of the exhibits, and the selection of lighting sources are fully considered. On the basis of ensuring that the cultural relics are protected from the hazards of optical radiation, the historical appearance of the cultural relics is truly presented to the audience, so that the audience can clearly see the details of the cultural relics.
1. Set the illuminance value and color temperature reasonably
According to their own materials, the exhibits can be divided into three categories: particularly sensitive to light, sensitive to light and insensitive to light. The illuminance value and color temperature of each type of exhibit can be determined with reference to the requirements in the Code for the Design of Museum Buildings (JGJ66-2015). Generally speaking, the illuminance should match the color temperature, that is, high illuminance and high color temperature light distribution, low illumination and low color temperature light distribution. As the color temperature increases, the wavelength of light is biased towards the short-wave range, and the violet and blue light components in the spectrum will increase, which will lead to damage to cultural relics such as weaving and embroidery and paper. Therefore, low illumination and low color temperature are more beneficial to the protection of cultural relics, but such a light distribution design will make people feel depressed and depressed, which is not conducive to the audience to appreciate cultural relics. In the lighting design of museum exhibits, the relationship between cultural relics protection and display effect should be properly handled. First of all, it is necessary to protect the exhibits to the greatest extent and ensure that they are not persecuted by optical radiation, and secondly, they should be designed according to the sensitivity of the exhibits to light. Generally, the protection of exhibits should be considered when irradiating exhibits that are particularly sensitive to light, and the light distribution method of low illumination and low color temperature should be adopted, especially the color temperature of the lighting source should not be higher than 3000K. For exhibits that are not sensitive to light, the main focus should be on the display effect of the exhibits, and the light distribution method of high illumination and high color temperature should be adopted to improve the visual comfort of the audience and be more conducive to viewing the exhibits (Figs. 1 and 2).
Figure 1 Example of ensuring the display effect of exhibits:
Exhibits of the "Forbidden City and the Grand Canal Special Exhibition" of the China Grand Canal Museum in Yangzhou
Fig.2 Example of ensuring the display effect of the exhibits: Cangzhou Museum blue glaze pile appliquéd dragon handle pot
2. Effectively limit the annual exposure of exhibits
The annual exposure of exhibits refers to the cumulative value of the illumination (illuminance × time) of the exhibits in a year, which is the most direct quantitative indicator of the damage effect of light on the exhibits. Although the Code for the Design of Museum Buildings (JGJ66-2015) stipulates the annual exposure limit of exhibits that are particularly sensitive to light and sensitive to light, it does not mean that the annual exposure does not exceed the limit value and the exhibits will be exempted from damage, in fact, it only plays a role in delaying the damage of exhibits. From the perspective of cultural relics protection, the environment for the preservation of cultural relics should avoid light, but the exhibition is the opposite, and it needs to have good lighting conditions. The annual exposure limit of the exhibits is only the limit of the acceptable damage range of the exhibits on the basis of satisfying the display effect. For example, exhibits that are particularly sensitive to light are limited to 50,000 lx·h/a per year, and can only be displayed for 1,000 hours per year without any measures to limit exposure, and the number of days such exhibits is only 125 days per year, that is, about 4 months, based on the daily display time of 8 hours. In order to effectively reduce the annual exposure and achieve the purpose of protecting the exhibits, domestic museums generally adopt the replacement of the exhibits after a period of time or the use of human body sensors to intelligently control the booth lights to realize the automatic on, dimming or closing of the lights, so as to shorten the irradiation time of the lights on the exhibits, which reduces the annual exposure of the exhibits to a certain extent, and also reduces the lighting energy consumption. However, neither method can accurately count the actual exposure data of exhibits, which is not conducive to effectively evaluating the annual exposure of exhibits, and it is difficult to realize the refined protection of cultural relics. At present, some museums in the industry have gradually carried out the systematic evaluation of the annual exposure of exhibits, and have achieved good results. For example, the Shanxi Museum uses the self-developed exposure recording analyzer to collect the daily illumination times, each illumination duration, daily cumulative exposure and other data of light-sensitive exhibits in real time, and through the intelligent statistical analysis of the background software, it provides scientific and systematic data support for the display time, display plan and exhibit protection of the exhibits, and plays a good role in application demonstration.
3. Adopt a lighting source with good performance
The selection of lighting sources for museum exhibits should comprehensively consider various parameters such as color temperature, luminous efficiency, color rendering index, ultraviolet and infrared content, and service life. This is because only a well-performing lighting source can truly present the original appearance of the artifact without being damaged by optical radiation, and better show its historical and artistic character to the audience (Fig. 3).
Fig.3 Examples of historical and artistic representations of cultural relics: Celadon Lotus Statue at the Six Dynasties Museum in Nanjing
(1) Reduce the hazards of optical radiation
The harm caused by optical radiation to cultural relics is closely related to the wavelength of light. In general, the shorter the wavelength, the greater the radiation damage caused to the cultural relics, especially the ultraviolet radiation with a shorter wavelength range. Through the statistics of various parameters of various light sources commonly used in the lighting of several museum exhibits, it is shown that incandescent lamps, fluorescent lamps, halogen lamps and metal halide lamps all contain ultraviolet or infrared rays to varying degrees, and are much higher than the limit value of ultraviolet radiation less than 20μW/lm in the light sources that irradiate light-sensitive and particularly sensitive exhibits, which will pose a hazard to cultural relics. In particular, the cultural relics of organic matter will be aggravated by ultraviolet radiation for a long time, and there will be discoloration and fading. Therefore, the use of these lighting sources in the lighting of museum exhibits requires additional configuration of accessories that filter ultraviolet or infrared rays, but this not only improves the operating cost, but also additionally increases the volume of lighting fixtures, which is not conducive to daily maintenance and maintenance, and also affects the aesthetics of lighting fixtures to a certain extent. The LED lighting source because its spectrum basically does not contain ultraviolet and infrared, especially the relative content of ultraviolet light in the high-quality LED lighting source is only 0.2~0.5μW/lm, so the use of LED lighting source in the lighting of museum exhibits does not need to install a filter device to prevent optical radiation, from the perspective of cultural relics protection, it has greater advantages than the traditional exhibition lighting source of the museum.
(2) Ensure the color reproduction performance of the lighting source
Only a lighting source with good color reproduction performance can present the true color of the exhibits to the audience, which is more conducive to the display of exhibits (Figs. 4 and Fig. 5). In the lighting of museum exhibits, the general color rendering index (Ra) is usually used as the evaluation index of the color rendering performance of the lighting source, which can be applied to the traditional lighting sources of museums such as halogen lamps, metal halide lamps, and incandescent lamps. In particular, for exhibits with high requirements for color discrimination, such as paintings, lighting sources with a general color rendering index (Ra) higher than 90 should be used. However, due to the uneven quality of LED lighting sources, the color rendering performance of some products is average, and the color reproduction effect of the red spectrum is poor. Therefore, for exhibits with high color discrimination requirements, if LED lighting sources are used, the general color rendering index (Ra) should not only be higher than 90, but also pay attention to the parameters such as red saturation color rendering index (R9), fidelity index (Rf) and color tolerance in the special color rendering index. Among them, the red saturation color rendering index (R9) is used as a measurement index to measure the reduction index of the red spectrum of the lighting source, which plays a crucial role in the evaluation of the color rendering performance of the LED lighting source. Relevant research in the industry shows that some museums in China still use the earlier LED lighting fixtures in the lighting of the exhibits, and have not been replaced and upgraded, coupled with the fact that the museum has not paid sufficient attention to the red saturated color rendering index (R9) of the LED lighting source, most museums have a low index, and the index is still negative in some museums, resulting in poor color reproduction performance of the lighting source, which cannot meet the needs of the exhibits for a high degree of color reproduction. The Fidelity Index (Rf) is the main index for evaluating the color rendering performance of lighting sources by the North American Society of Lighting Engineers. Because it uses 99 color test samples, it is more comprehensive than the general color rendering index (Ra) that only uses 8 color test samples, so it is also another important indicator to measure the color reproduction performance of LED lighting sources. Color tolerance is an important value to measure the color consistency of similar lighting sources. Therefore, in the lighting of museum exhibits, it is necessary to choose an LED lighting source with a red saturated color rendering index (R9) higher than 50, a fidelity index (Rf) greater than 90, and a color tolerance not higher than 3SDCM, which is used to illuminate the exhibits with high requirements for color discrimination, so as to ensure high-quality color restoration effect and better show the original historical appearance of cultural relics for the audience.
Figure 4 Example of ensuring the color reproduction performance of the illumination source:
Grand Canal Museum, Beijing
Qing Qianlong Jingdezhen kiln outside pastel, blue and white hollow flower and fruit pattern hexagonal set of bottles
Figure 5 Example of ensuring the color reproduction performance of the illumination source:
Zhejiang Provincial Museum Zhijiang New Museum Longquan kiln celadon boat-shaped inkstone
(3) Avoid the strobe influence of lighting sources
Strobe refers to the phenomenon that the brightness of the light jumps and becomes unstable due to the periodic light and dark fluctuations of the illumination source. Severe flicker of lighting sources will have a great impact on the visual experience of the audience and the clarity of the image when shooting on site. In particular, visible strobe with a light output frequency within the range of 80Hz will directly cause visual fatigue to the audience, which will greatly affect the visual experience of the audience, and even cause symptoms such as blurred vision and dizziness. Invisible flickers with light output frequencies in the range of 80Hz to 500Hz will affect the effect of on-site photography and media broadcasting, resulting in unsatisfactory image clarity. Among the lighting sources of museum exhibits, the strobe problem of LED lighting sources is more common. Research on the strobe of LED lighting sources in the industry shows that the strobe problem is mainly related to the frequency and depth of the light output. Therefore, if the LED lighting source is used in the lighting of museum exhibits, the strobe problem should be considered, and the LED lighting source with a light output frequency of not less than 500Hz and a low strobe depth should be selected to effectively avoid the adverse effects caused by the strobe of the light source.
(4) Choose a lighting source with high luminous efficiency and long service life
The selection of lighting sources for museum exhibits should also focus on the luminous efficiency and service life of the light source, so as to better achieve the purpose of energy saving, environmental protection and reducing operating costs. Through the statistics of various parameters of several commonly used light sources in the lighting of museum exhibits, it is shown that the luminous efficiency of incandescent lamps and halogen lamps is low, while the luminous efficiency of LED lighting sources is 130lm/w, which has certain advantages compared with other lighting sources. In terms of service life, LED lighting sources can reach 80,000 to 100,000 hours, which is significantly higher than other lighting sources. With the rapid development of its technology, it has begun to be widely used in the lighting of exhibits in major museums at home and abroad in recent years, and has gradually replaced the traditional lighting source of museums. For example, in 2009, the National Museum of Korea replaced the traditional halogen lamps with LED lighting sources in the lighting of exhibits, which not only played a good role in the protection of exhibits, but also calculated that the lighting energy consumption was less than 25% of the original, thus effectively saving a lot of energy and reducing the operating costs of the museum. Since then, the Louvre Museum in France and the Rijksmuseum in the Netherlands have also used LED lighting sources in the lighting of exhibits, and have achieved good application results. Since 2010, many domestic museums, such as the Guangdong Provincial Museum, the Palace Museum, the Nanjing Museum, the Hebei Museum, the South China Sea Museum of China (Hainan), and the Jiangxi Provincial Museum (New Museum), have successively used LED lighting sources in the lighting of exhibits, which not only enhances the display effect of the exhibits but also effectively enhances the artistic appreciation of the exhibits while protecting the exhibits and greatly reducing the lighting energy consumption (Figure 6).
Fig.6 Example of the artistic viewing effect of the exhibits: the bronze cymbal of the new Jiangxin Hall of the Zhejiang Provincial Museum
The above analysis of the parameters of the commonly used light sources in the lighting of museum exhibits shows that the LED lighting source is significantly better than other lighting sources in the museum because of its high light efficiency, low power consumption, long service life, and the fact that the spectrum basically does not contain ultraviolet and infrared rays. However, if LED lighting sources are selected in the lighting of exhibits, their color reproduction performance and strobe problems need to be paid attention to.
IV. Conclusion
As an important part of the exhibition environment of the museum, the lighting of exhibits directly affects the protection of cultural relics in the museum and the visual experience of the audience. The design should be based on the basic principles of protecting the exhibits and facilitating the audience's appreciation of the exhibits, and properly handle the relationship between the two. According to the sensitivity of the exhibits to light and the requirements of the exhibition design, the illuminance value and color temperature are reasonably set, effective technical measures are taken to limit the annual exposure of the exhibits, and on the basis of comprehensive consideration of the color temperature, luminous efficiency, color rendering index, ultraviolet and infrared content, service life and other parameters of the lighting source, the lighting source with good performance is selected, and the original appearance of the cultural relics is truly presented for the audience under the premise of avoiding the damage of optical radiation to the cultural relics, and their historicity and artistry are better displayed. So that the audience can fully feel the cultural connotation contained in the exhibits.
This article was originally published in The Collector, Issue 2, 2024