This experiment differs from the control variable method adopted by most scientific research articles. It does not strictly control one variable to ensure the controllability of other factors and to strictly explore the relationship between various parts of the variable by changing only one variable. The paper is mainly to study the four different dimensions in a large space environment for observers to experience the psychological feelings of museum lighting, it is not a separate investigation of CCT and illuminance changes, but specific indicators in the actual museum environment are used for investigation and research. Correlation analysis and one-way analysis of variance were used to analyze the differences in four dimensions under three different lighting environments. In terms of the visual assessment temperature, based on the existing research results, we begin from four dimensions: comfort, clarity, preference and warmth.
The main survey of the comfort level is the coordination of the overall space light and shadow of the museum exhibition space, as well as the degree of psychological colour. Clarity checks whether the details and texture of the exhibits can be clearly displayed, which is satisfactory. Preference is that the overall artistic effect of lighting is outstanding, there are wonderful lighting performance effects and whether the lighting environment in which you are feeling the like. The warmth refers to the contrast of warmth and coldness on the senses, whiter means colder and yellower means warmer.
2.2. Museum Lighting Environment
This experiment adopts lighting environment parameters of three museums to study the factors affecting psychological perception via different lighting methods (Only the lighting environment and typical paintings and background were evaluated). Dang R et al. studied the effects of illumination on inorganic pigments used in traditional paintings, they think that high illuminance could be a problem for some museum objects including textiles, tempera paints, etc. [
18].
It selected 31 observers, aged 20–24 years. The first museum is the national museum of western art
Figure 2a. The measuring is the painting exhibition room of the 19th–20th century. The illuminance is direct illuminance, CCT = 2079 K, x = 0.5239, y = 0.4208, colour rendering index Ra = 96, R9 = 92, average illuminance Eav = 84 lx. The second museum is the Aichi art museum
Figure 2b. The measuring is the permanent exhibition room. The illuminance method is indirect illuminance, CCT = 2960 K, x = 0.4409, y = 0.4073, colour rendering index Ra = 90, R9 = 46, average illuminance Eav = 115 lx. The third museum is the Yamazaki Mazak art museum
Figure 2c. The measuring is the painting exhibition room on the fifth floor. The lighting method is mixed lighting, CCT = 3568 K, x = 0.4130, y = 0.4196, colour rendering index Ra = 93, R9 = 88, average illuminance Eav = 538 lx. The parameters of CCTs and illuminance in the three lighting environment experimental spaces is within Kruithof’s rule [
19].
CCTs analysis of the three lighting environments is shown in
Figure 3. The first and second lighting environments CCT light color slant yellow, giving us a warm feeling. The CCT of the third lighting environment is white, which is a warm white light.
CRI analysis of the three lighting environments is shown in
Figure 4. The R9 of the three art museums is 46, 92 and 88. CCTs, x and y are used to describe the CIE1931 chromaticity. The three spaces use different light sources and spectra, this method is used to define and quantify the parameters of the art museum lighting environment. And the CCTs in art museum lighting is different, which brings different visual experience and feeling to the observer. The lower the CCT, the warmer the hue of the art museum space; the higher the CCT, the cooler the hue of the art museum space and different CCTs give different subjective feelings. In order to accurately represent the colour of the lighting environment. The study uses the x and y values to give the position of the Correlated colour temperatures (CCTs) in CIE1931 accurately and provide more detailed optical data.
The R9 is a very important evaluation index for museum lighting. R9 is saturated red, it is an indicator of the ability of the light source to restore the redness of the object. The larger the value of R9, the higher the ability of the light source to reduce the redness of the object. The LED light source used in most museums is blue light to excite yellow phosphors to emit light. The value of the red light spectrum in the spectrum of this light source is relatively low, but the red spectrum is important in the lighting of art museums, the R9 value was used as an important indicator of evaluating the quality of the lighting environment.
People have maintained close ties with architecture. The size of the space inside a building also determines whether the lighting environment is comfortable for us. Good lighting design is inseparable from understood its architectural and space environment. The research classified the types of space, lighting and exhibits of three art museums. This type of research approach can be better defining the lighting environments of the space and exhibits.
The illuminance distribution in the national museum of western art lighting environment is shown in
Figure 5a, the arrangement and elevation of the direct lighting display source is shown in
Figure 5b. Direct lighting is adopted in the lighting environment. The lights shine directly into the middle of the paintings in the museum, highlighting the position of the paintings. The national museum of western art is installed with track on one side of the roof area by use of spotlights for direct lighting is shown in
Figure 5.
Figure 6 shows the paintings used in the national museum of western art lighting experiment, shows the 13 illumination distribution test points include typical oil painting and background wall. It was drawn by Claude Monet from French, an impressionist painter. The oil painting title is morning on the seine. The oil painting size is 82.0 × 93.0 cm, painting date in 1898. The average illumination of the oil painting and background wall is 225.4 lx, the minimum illumination is 180.2 lx, and the uniform of illumination is 0.80.
The illuminance distribution in the Aichi Prefectural museum of art lighting environment is shown in
Figure 7a, the arrangement and elevation of the indirect lighting display source is shown in
Figure 7b. Indirect lighting is adopted in the lighting environment. The light source shines on the ceiling, illuminating the entire lighting environment with reflected light. The Aichi Prefectural museum of art has LED lamps arranged roof with indirect lighting is shown in
Figure 7.
Figure 8 shows the paintings used in the Aichi Prefectural museum of art lighting experiment, shows the 13 illumination distribution test points include typical oil painting and background wall. It was drawn by Rinen Hoshi from Japan, a contemporary painter. The oil painting title is spring colorful flowers. The oil painting size is 180.6 × 86.4 cm, painting date in 2016. The average illumination of the oil painting and background wall is 117.6 lx, the minimum illumination is 148.5 lx, and the uniform of illumination is 0.84.
The illuminance distribution in the Yamazaki Mazak museum of art lighting environment is shown in
Figure 9a, the arrangement and elevation of the mixed lighting display source is shown in
Figure 9b. Mixed lighting is used in the lighting environment. Both the light source directly illuminating the painting and the light source illuminating the ground are combined. The Yamazaki Mazak museum of art is equipped with an average arrangement for LED recessed downlights. A series of singlets allow additional accent lighting using spotlights is shown in
Figure 9.
Figure 10 shows the paintings used in the Yamazaki Mazak museum of art lighting experiment, shows the 13 illumination distribution test points include typical oil painting and background wall. It was drawn by Jean-Marc Nattier from Paris, a rococo painter. The oil painting title is sailboat in the morning. The oil painting size is 101.8 × 82.8 cm, painting date in 1739. The average illumination of the oil painting and background wall is 381.9 lx, the minimum illumination is 331.4 lx, and the uniform of illumination is 0.87.
2.3. Psychophysical Experiment
Luo et al. did two experiments. Experiment 1 was to study the influence of lighting conditions on visual perception in the light box and proposed the semantic differential scale of 11 adjective pairs, which are designed to be related to perceived appearance and atmospheric perception. Experiment 2 was made in an actual museum and 10 adjectives were proposed [
10]. Based on the 10 adjectives, this paper extracts 4 semantic differences about the environmental atmosphere, which is comfort, clarity, preference and warmth.
This experiment applies the method of categorical judgment in the psychophysical experiment method. The observer performs subjective scoring of comfort, clarity, preference and warmth in three different lighting environments.
A minimum of 1 point means completely not comfort/clarity/preference/warmth, a score of 2 means not comfort/clarity/preference/warmth, a score of 3 means less comfort/clarity/preference/ warmth, a score of 4 means relatively comfort/clarity/preference/warmth, a score of 5 for comfort/clarity/preference/warmth, and up to a score of 6 for very comfort/clarity/preference/warmth.
Table 1 gives an example for scoring comfort level, the description of the scores and the meaning of each category.
Figure 11 shows the exhibition space of the art museum is classified in terms of architectural functions, it is mainly divided into viewing space, traffic space and rest space. Observers have different visual focuses in different spaces. In the rest space and the traffic space, the observer’s visual focus is mainly the overall space, use the illumination of the ground in the lighting environment was used for evaluation. The main task in the viewing space is to appreciate artistic works, observer’s visual focus is on the background walls and oil paintings, use the typical oil paintings and background wall illumination were used for evaluation.
The experimental process is as below:
Introduction. Introduce the content and process of the art museum lighting experiment to the observer.
Visual testing. Test the observer for visual defects or color blindness.
Environmental adaptation. The observer first adapts to the museum lighting environment under a typical space for about 2 min. The experiment should allow the observers to whole experience the art museum lighting environment of the exhibition space and evaluate and feel the lighting environment of the viewing space, traffic space and rest space through observers’ vision.
Main experiment. Through the moving, viewing and staying of the observer in the exhibition space visual task is completed, the process takes about 5 min. Next, observers viewing the typical painting lighting environment in the viewing space, observe the oil paintings and feel the lighting environment in the viewing space, the process takes about 3 min.
Figure 12 shows the observation distance of the observers when viewing the oil painting. A limit is set before each painting to control the viewing distance to ensure that the observer’s sightline is at the best viewing angle and distance. The typical size of the oil painting used in this experiment is suitable, so the observers are looking to have the optimal visual distance.
- 5.
Subjective evaluation. The observer makes a subjective evaluation of the current lighting environment in the art museum, the observer fills in the corresponding score according to the questionnaire. The experimental process obtained subjective response data through four evaluation dimensions (comfort, clarity, preference and warmth) from observers. And analyzes the influence of the actual spatial lighting parameters of art museum buildings on observers’ psychological emotions.
- 6.
Museum lighting environmental changes.
- 7.
Repeat steps 3–5 until the experimental data are collected.
2.4. Observer Difference Analysis
The same 31 observers selected went to three museums for field research and data evaluation. Each was evaluated for comfort, clarity, preference and warmth in three lighting environments, and 93 groups of subjective evaluation data were obtained. In this experiment, the Coefficient of variation (CV) is adopted to compare the data stability among observers [
20].
This is an example of an equation:
In Equation (4), the score for the i-th observer is , the mean for all observers is , N is the number of observers, where N = 31.
Table 2 indicates the CV for the evaluation scores in different lighting environments. Environment 1 is the national museum of western art. Environment 2 is the Aichi Prefectural museum of art. Environment 3 is the Yamazaki Mazak museum of art. It’s verified that the data in
Table 2 are within the normal limits of the psychophysical experiment CV, the data obtained from the psychophysical experiments in this study are all reliable.