Simulation and perceptual evaluation of fashion shop lighting ...

Research Article

Building Thermal, Lighting,

and Acoustics Modeling

E-mail: [email protected]

Simulation and perceptual evaluation of fashion shop lighting design with application of exhibition lighting techniques

Tae-Kyoung Ko, In-Tae Kim, An-Seop Choi (), Minki Sung

Department of Architectural Engineering, Sejong University, Kunja-Dong, Kwangjin-Gu, Seoul, 143-747 R.O. Korea Abstract Fashion shops employ visual merchandising strategies to display products through improvement of luminous environment, which can enable customers to better appreciate fashion products. Such a strategy can eventually increase sales. This study proposed a lighting plan for fashion shops that applies exhibition lighting techniques. First, a fashion shop lighting plan was proposed based on exhibition lighting techniques in museums, and a subjective evaluation was performed by simulation and visualising the design of fashion shop lighting considering various parameters. The characteristics of preference, perceptual clarity and visual attention were assessed for various lighting and correlated color temperature (CCT) conditions. Various display lighting methods in fashion shops for mannequins, tables and hangers were also evaluated. Then, an overall assessment for these objects based on the results of the subjective evaluation was discussed.

Keywords fashion shop lighting,

museum lighting,

subjective evaluation,

lighting simulation Article History Received: 4 January 2016

Revised: 7 July 2016

Accepted: 21 July 2016 © Tsinghua University Press and

Springer-Verlag Berlin Heidelberg

2016

1 Introduction

1.1 Study purpose

As customers’ lives are enriched by social progress, a new era has arrived for customers to pursue individual styles. Fierce competition has arisen in the fashion market to accommodate the diverse demands of consumers. Therefore, fashion shops attempting to survive such competition have implemented a strategy called visual merchandising to attract consumers and increase their purchasing demand (Kwon and Shin 2009). Visual merchandising is a strategy that combines visualisation and merchandising plans for product display, and the visual elements employed are representative environmental elements that attract the consumer’s attention to stimulate purchasing demand. Lighting affects product sales by enhancing visual merchandising effects, and product display lighting has a greater impact on consumers than general lighting (Kim and Hong 2012). Display lighting is not only used to simply illuminate products, but it also creates an environment in which properly lit products can stimulate a consumer’s emotions via the lighting angle,

method and light source. However, previous studies on fashion shop lighting

have been limited to studies on the aesthetics and psychology of consumers; studies that specifically suggest particular lighting schemes for fashion shops are lacking. A preliminary study for this paper was conducted by surveying fashion shop lighting (Ko et al. 2015). This assessment was carried out on fashion retail stores that carried mid- and low-priced brands that were visited by many consumers as well as in luxury brand shops that carried expensive brands. The lighting strategies used for mannequins, tables and hangers were investigated in 14 retail fashion stores and 4 luxury brand shops. The study confirmed the need to improve fashion shop lighting, and the application of display lighting used in museums as lighting in fashion shops was reviewed.

The most important function of fashion shop display lighting is to reveal the essence of the products displayed and to make them stand out. Most museums use various lighting methods for each object displayed and the types of objects displayed in museums are similar to products displayed in fashion shops. In fact, vertical illuminance can play an important role in enhancing visual perception in

BUILD SIMUL (2016) 9: 641–658 DOI 10.1007/s12273-016-0312-5

Ko et al. / Building Simulation / Vol. 9, No. 6

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both museums and fashion shops (Schielkea 2013). Fashion shops must use lighting that emphasises certain aspects of products so that consumers can properly understand each product, which ultimately leads to sales. However, proper proportion of lighting and shadow in fashion shop displays should be maintained with an appropriate level of general lighting. If there exists an excess in either one of them (lighting and shadow), product details cannot be seen, or recognition of color appearance can be affected.

In this study, the use of exhibition lighting techniques in museums was proposed as a lighting plan for fashion shops. Various options of the lighting design reflecting different illuminance and correlated color temperature (CCT) conditions were suggested, and a subjective evaluation was performed by simulating various lighting designs on a computer monitor. The subjective evaluation of various lighting design option in a mock-up space is the best methodology to investigate a proper lighting design in a fashion shop. But only limited options of the lighting design can be performed to carry out this evaluation effectively. Otherwise, due to many independent variables, this research would take a long time to get reasonable results. To assess various options of the lighting design, the method of lighting simulation is a proper option. The lighting simulation is basically performed to identify the quantitative luminous values including illuminance and luminance. In addition, the rendering images by lighting simulation is also required to assess luminous environment qualitatively.

An overall assessment for the lighting in each part of the fashion shops was discussed based on the results of the subjec-tive evaluation. Because the lighting was presented by displaying simulation images on a computer monitor, the results of this study are also applicable to on-line apparel shopping malls, which must display their products realistically and vividly.

1.2 Previous research

A study was conducted to examine the correlation between the lighting method in fashion shops and purchasing sentiment (Kim 2001). The study found that some stores did not have a sufficient understanding of lighting and that consumers correlated a pleasantly lit environment with purchasing demand. Durak et al. (2007) also found a statistically significant difference in lighting arrangements regarding preference and other specific impressions. They found that wall washing and cove lighting were preferred lighting arrangements and created different impressions. In addition, Summers and Herbert (2001) conducted a consumer study to analyse the effect of display lighting on the compositional elements in a store space. Lighting was found to have positive effect on product selection and consumption by consumers. Similarly, Custers et al. (2010) surveyed the effect of mood recognition

lighting in the fashion retail environment and found that lighting plays an important role in mood recognition. Moreover, Barlı et al. (2012) studied the relationship between lighting and interior colors in stores and purchases. They found that the time spent in a store had a statistically significant effect on the purchasing of products that had a green color. Soft lighting yielded a positive response during time spent in stores, and the color red had a negative tendency. A similar study was conducted to show the effects of color and light on indoor wayfinding and the subjective judgement of the perceived environment (Hidayetoglu et al. 2012). The results showed that attractiveness and memorability of warm colors were higher, whereas cool colors and a high brightness level could help people orient themselves in a space. Furthermore, the role of lighting on a consumer’s perception was investigated (Quartier et al. 2014). They suggested that investing in lighting is a valuable strategy for a successful retail environment despite the absence of a statistically significant effect for an individual outcome regarding relative lighting differences.

The quantitative aspect of the lighting in fashion shops was examined. Schielke and Leudesdorff (2015) analyzed the effect of brand personality in fashion shop lighting on consumers, conducting a study on luminance and intensity of light in fashion shops. A study by Mouhoubi (2014) more specifically examined physical quantity of lighting in fashion shops by analyzing the effect of lighting condition and shelf height in fashion shops on emotional status of consumers. The result showed a tendency that lighting affects information of products and approach behaviour of consumers to the retail environment, enhancing visual recognition of consumers to guide their emotional status. Also, Dikel and Yener (2007) developed a lighting coordinate database that is useful for illuminating 3D art objects based on the artists’ opinion.

Previous studies of fashion shop lighting considered consumer sentiment about the luminous environment, the effect of the luminous environment on products, and lighting methods. No lighting design studies have actively attempted to maximise the visual effect of products.

2 Research background

2.1 Fashion shop lighting

Lighting conditions in fashion shops must attract consumers’ attention and allow them to accurately recognise products (Rea 2000, p. 662). Both display lighting and general lighting conditions are important. In addition, the lighting must be designed to attract a consumer’s eye and allow for the accurate recognition of a product’s characteristics.

Mannequins attract a consumer’s attention, providing a highly effective fashion display. The lighting of a mannequin


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must effectively convey the value and fashion of a product to the consumer by communicating vividness and a three- dimensional (3D) impression (Fig. 1).

Hangers lead the consumer to purchasing by conveying information of products (Fig. 1). Because the same products tend to be displayed together on hangers, the lighting provides uniform brightness for all products and the vertical aspects of the products displayed should be considered.

Large quantities and many types of products can be displayed simultaneously on some tables, whereas others contain an arrangement of smaller quantities of selected products (Fig. 2). The purpose and lighting method differ between the two types of table displays. For the lighting for a table that displays a large quantity of products, high-CRI lighting that is widely distributed must be used to shed light on each of the various products. On the contrary, a table that displays a small quantity of selected products must convey the shape, texture and 3D form of the products with proper use of lighting.

There are two types of showcases, as shown in Fig. 2: the enclosed type and the shelf type. The lighting for a showcase must be direct and high-CRI lighting that is widely distributed must be used to shed light on each of the various products displayed on the shelves.

Fig. 1 Fashion shop images of mannequin and hanger

Fig. 2 Fashion shop tables and showcases

2.2 Museum display lighting

The role of display lighting in museums is to attract the attention of the audience in a pleasant and comfortable environment, to show the displayed objects as they are, to allow for appreciation, and to help preserve the displayed objects (Kim 2004).

Objects such as oil paintings and documents are hung on a wall, and the vertical aspect is important. The lighting must have a minimum illuminance to maximum illuminance ratio of 70% or higher for uniform illuminance to the object illuminated, and the eye of the viewer must form a 60° angle between the planar object and light source. Additionally, the position of the light source with respect to the displayed object is calculated according to Eq. (1) (Rea 2000, p. 603).

(Ceiling height – Human eye level) × 0.577 = Horizontal distance from the displayed product to the luminaire (1)

The luminous environment for 3D objects, such as sculptures and other large-sized works, must change illuminance in different directions to emphasise shape and texture of the displayed object, allowing a 3D impression through 3D shading. This lighting method of 3D objects uses four types of lights. First, the key light that does not diffuse and sheds light from above at an angle of 45° to the eyes of the viewer is used. Second, the fill light supplements the key light on the opposite angle. The fill light is weaker than the key light. Third, the back light drops down from the background to reflect the object of display from behind. Fourth, the background light floats in the background to make the object stand out. Figure 3 shows three types of lights, excluding background light (Rea 2000, p. 608). The key light and fill light are the most commonly used, and back lights can be added depending on the size of the object displayed.

Fig. 3 Sculpture lighting: Alan Houser’s Apache Warrior. Los Angeles County Museum of Natural History, 1982 (Rea 2000, p. 608)


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3 Subjective evaluation and simulation modeling

3.1 Subjective evaluation outline and methodology

A subjective evaluation was performed by simulating images using museum display lighting to the luminous environment in fashion shops. A subjective evaluation method must be appropriate for the purpose and characteristics of the study to which it is applied. Experimental subjective evaluation methods for lighting include a side-by-side test, a photo- image test and a field test, and comparison methods include sequential comparison and simultaneous comparison (Fotios and Cheal 2010). Side-by-side tests are used to investigate simple brightness recognition and viewer preference for spectral distribution and correlated color temperature. Photo- image tests are mainly used as an experimental method to survey preferences for different parameters, and field tests are used to survey brightness recognition and preferences for variable luminous environment. Sequential comparison allows for independent and objective evaluations of the effects of brightness while simultaneous comparisons can highlight differences in the luminous environment by the time it takes for a viewer to compare objects.

Schielke (2010) reported a subjective evaluation using a photo-image test that determined the effect of different luminous environments on the image of a commercial space using a simultaneous comparison method. Park et al. (2010) conducted a highly objective study, performing an indirect comparison using a simultaneous comparison method via a photo-image test and a direct comparison using a sequential comparison method via a field test at the same time. Through modelling the architectural spaces by RADIANCE simulation and its rendering images were assessed by subjective evaluations for a natural light impact on the space according to the facade design variables (Aries et al. 2014), and preferred simulation images were evaluated for daylight- responsive lighting using the shading system (Mahdavi 2008). In addition, daylighting design options for museum lighting were evaluated by RADIANCE simulation (Kim and Seo 2012).

Our study used subjective evaluation based on simulated

images with different characteristics. A field test is appropriate for a survey of viewer preferences according to the actual performance of work, and a side-by-side test is appropriate for a survey of preference for the luminous environment with simple characteristics. Based on the previously mentioned studies, a photo-image test using the simultaneous com-parison method, rather than a field test or a side-by-side test, was determined to be appropriate for the visualisation of lighting simulations to determine viewer preferences for different lighting scenarios.

Lighting simulation images were created in this study by using general exhibition lighting techniques as used in museums. The use of such general techniques is a first step for the improvement and specialised design of fashion shop lighting. Simulation images can be evaluated using a monitor, beam projector or photograph. A beam projector can allow for the evaluation of images on a large screen, but the shape and color of the projected image can be distorted by the surrounding environment, and the resolution is also problematic. A photograph can easily persuade a viewer that it is based on reality, but the resolution and color of photograph can cause negative emotions. A monitor was chosen as appropriate for our subjective evaluation because screen display properties could be adjusted to create a familiar visual environment for subjects. But, colors shown on a computer monitor vs. the actual items could not be exactly same. To minimize the effect of this matter, less saturated color fashion items were selected.

In the monitor experiment, the quality of the monitor screen referred to as brightness at Recommendation ITU-R BT 500-13 (ITU-R 2012), the chromaticity of background, and the distance of the viewer from the monitor were tested. In addition, the vertical illuminance was set to 200 lx on the computer monitor based on Recommendation ITU-R BT 500-13 where the illuminance and CCT values could be changed using dimmable LED luminaires. The luminance of the monitor was adjusted by measuring the white color as 70 cd/m2, and a subjective evaluation was performed after setting the background chromaticity to D65 and distance of the viewer from the monitor to 900 mm. The resolution of the monitor used was 1920 × 1080 (Fig. 4). The CCT from

Fig. 4 The subjective evaluation images


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the sample images and simulated rendering of images on the monitor screen were evaluated and identified with a Chroma meter (CL-200A).

The subjective evaluation was carried out on 20 subjects including 10 ordinary persons without abnormal vision and 10 persons with expert knowledge in lighting (Table 1). We had an intension to investigate how the results will be different according to the knowledge in lighting.

Lightscape 3.2 was used for visualization of the lighting simulation in this study (Autodesk 1999). Lightscape 3.2 is a lighting software that expresses realistic lighting effects. Space was formed and imported from 3D modelling software such as 3D Max, Auto CAD and SketchUp, and 3D modelling objects were also imported. A luminous intensity distribution file was selected for the luminaire to perform lighting calculation and create a rendering image that expresses the lighting effect. The IES format files of luminous intensity distribution data were used for the model of the light sources and luminaires in simulation. The IES format file also contains initial rated lumens and the dimensions of the luminaires including the width, length and height of the luminous opening. To simulate different CCT light sources, the chromaticity coordinate values (XYZ) for 3000 K and 4500 K light sources were selected from blackbody chromaticity values and converted to RGB values using color conversion formulas (XYZ —> RGB). Then, those RGB values were used for input data in simulation. In this Lightscape 3.2 simulation, the receiver mesh spacing setting was min. 176 and max. 880. The tolerances length setting was 0.5, and ray offset setting was 5. The partial materials were applied to texture map (jpg format image) and rendering format setting was jpg file format (image resolution setting- 1916 × 915). And, the ray tracing was set to ray bounces: 10.

Simultaneous comparison using a tournament technique was the evaluation method. In the tournament technique,

Table 1 Test subject outline

Type Specification

Sex Male 7, female 13

Organization Undergraduates and graduate students in the department of architectural engineering, lighting professionals in Seoul

Age 20 – 30

Glasses Contact lens Nothing

3 2 15

Color blindness Color

weakness NormalityEyesight conditions

0 0 20

Total number of people 20

the viewer continuously compares lighting images until a final lighting image is selected from all of the images provided. This method of selecting an image from a small number of images was considered to be more objective than reviewing a large number of images at once. However, because the lighting images were randomly presented to the subject, highly preferred images might be eliminated when different images of similar preference were presented. Therefore, this experiment used the tournament technique shown in Fig. 5 based on an appropriate ordering of the images. The tournament method gave a score of 3 points for images ranked 1st, 2nd and 3rd, 2 points for images ranked 4th, 5th and 6th, and 1 point for images ranked 7th through 12th. The simulation image that obtained the highest overall score was selected as the preferred image. The image set consisted of 24 mannequin images, 22 table images and 12 hanger images. Six simulation images were simultaneously shown to the viewer on the monitor during the subjective evaluation. Table 2 shows the evaluation questionnaire for mannequins, tables and hangers. Questionnaire items were selected based on conventional previous studies.

Fig. 5 Selection process using tournament technique

Table 2 Questionnaire of subjective evaluation

No. Contents

1 Preference <mannequin, table and hanger>

2 Perceptual clarity <mannequin, table and hanger>

3 Visual attention <mannequin, table and hanger>

3.2 Simulation rendering image

3.2.1 Mannequin lighting

The position of the luminaires for the mannequin was configured by applying dimensional display lighting as


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in museums. The lighting method using key light and fill light was used, and the key light and fill lights were positioned 1500 mm to the left and right sides of mannequin. The vertical distance from the mannequin was 1000 mm (Fig. 6).

Parameters for the mannequin lighting included the angle of key light beam, the illuminance ratio of the key light and fill light, the illuminance ratio of the background, and the color temperature. The mannequin lighting image is as shown in Table 3. The angle of key light beam was set at 10° and 20°, as generally used in display lighting, whereas the angle of the fill light beam was set more widely at 30° (Fig. 7). The illuminance ratio of the key light to the fill light was set at 1:1, 3:1 and 6:1, and the values were determined according to incidence of the light on the mannequin. The illuminance ratio of the background refers to the ratio of

the object displayed to the illuminance of surrounding objects other than the displayed object, and this ratio was set at 1:5 and 1:10 (background: key light). A value of 1:5 is generally applied to display lighting in museums as the illuminance ratio for the background (DiLaura et al. 2011), but a larger value of 1:10 was applied in this study because fashion shops require brighter lighting compared to museums. A large difference in the background illuminance ratio allows the displayed object to stand out, but a viewer’s eyes can become fatigued. A small difference in the illuminance ratio can result in poor display of products, which might then not exhibit 3D effects properly.

The subjective impression for color temperature was set to 3000 K as the low color temperature and 4500 K as the high color temperature (Manav 2007). A low color tem-perature is widely used in fashion shops for a luxurious

Fig. 6 Outline of the mannequin simulation (elevation drawing & floor plan)

Table 3 Simulation images for lighting variables of mannequin (a) Background illuminance ratio 1:5

The ratio of lighting fixtures illuminance (key light : fill light)

Lighting fixture Color temperature 1:1 3:1 6:1

3000 K

Key light 10° Fill light 30°

4500 K


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(Continued)

3000 K


4,500 K

(b) Background illuminance ratio 1:10

The ratio of lighting fixtures illuminance (key light : fill light)

Lighting fixture Color temperature 1 : 1 3 : 1 6 : 1

3000 K

Key light 10 ° Fill light 30 °

4500 K

3000 K

Key light 20 ° Fill light 30 °

4500 K

Note: All mannequin images are resized by cutting the space between woman and man to show the image in the small table.


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image because it can engender warm, comfortable and cosy feelings (Bullough 2005). In contrast, a high color temperature can create a vivid atmosphere with cool and pleasant feelings and is mainly used in casual fashion shops to create a cheerful mood. Table 4 shows the illuminance values used for mannequin lighting, measured at the centre of the mannequin’s chest (vertical illuminance). The vertical illuminance range applied was from 90 to 450 lx, excluding

Table 4 Vertical illuminance values for mannequin (at the center of the chest) (a) Background illuminance ratio 1:5

The beam angles of lighting fixtures


1 : 1 75 lx 75 lx

3 : 1 75 lx 25 lx The ratio of lighting fixtures

illuminance (key light : fill light) 6 : 1 75 lx 15 lx*

* 15 was used instead of 12.5 because the minimum value was set to 15 lx.

(b) Background illuminance ratio 1:10 The beam angles of lighting

fixtures Key light 10° Fill light 20°

1 : 1 150 lx 150 lx

3 : 1 150 lx 50 lx The ratio of lighting fixtures

illuminance (key light : fill light) 6 : 1 150 lx 25 lx

the background illuminance (ambient lighting). The back-ground illuminance was created by uniform general lighting over the space, and its value was set 15 lx, measured horizontally at the floor level.

3.2.2 Table lighting

The position of the luminaires for the table was configured by using museum dimensional display lighting, as shown in Fig. 8. A back light was used in addition to the key light and fill lights.

For table lighting, even a narrow beam angle can shed light on the entire product because small-sized products are placed at a low height. Therefore, the beam angle was fixed at 10° for the key light and 20° for the fill and back lights. The illuminance ratios of the key light, fill light and back light, the background illuminance ratio of the display illuminance to the illuminance of objects other than the display, and the color temperature were selected as shown in Table 5.

The ratio of key light: fill light was set at 1:1, 3:1 and 6:1. When the back light was added, the ratio of key light: fill light: back light was set at 1:1:1 and 3:1:1. These are values used in typical display lighting. Background illuminance ratio and color temperature were identical to the parameter settings for mannequin.

Table 6 shows the illuminance values used for table lighting, measured at the centre of products. The illuminance

Fig. 7 Relative luminous intensity distribution curves for three luminaire beam angles

Fig. 8 Outline of the table simulation (elevation drawing & floor plan)


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Table 5 Simulation images for lighting variables of table(a) Background illuminance ratio 1:5

Color temperature The ratio of lighting fixtures illuminance (key light : fill light : back light) 3000 K 4500 K

1 : 1 : 0

3 : 1 : 0

6 : 1 : 0

1 : 1 : 1

3 : 1 : 1

(b) Background illuminance ratio 1:10

Color temperature The ratio of lighting fixtures illuminance (key light : fill light : back light) 3000 K 4500 K

1 : 1 : 0

3 : 1 : 0

6 : 1 : 0

1 : 1 : 1

3 : 1 : 1


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differed according to the beam angle of the key light and fill light, as well as for the background illuminance ratio. The range of the vertical illuminance and the range and method of the background illuminance were the same as for the mannequin. The luminous intensity distribution curve of the luminaires used at an angle of 10° for the key light, 20° for the fill light, and 20° for the back light is shown in Fig. 9.

Fig. 9 Relative luminous intensity distribution curves for two luminaire beam angles

3.2.3 Hanger lighting

The position of the luminaires for the hanger was configured as planar display museum lighting. One luminaire was used, and the horizontal distance from the product to the luminaire is as expressed by Eq. (1) (Section 2.2) (Rea 2000, p. 603). The horizontal distance was set to 870 mm; this value was computed by subtracting approximately 1500 mm as the human eye level from the ceiling height and multiplying by 0.577 (Fig. 10).

The beam angle of the luminaire, the direct wall illuminance, and the color temperature were used as parameters and are shown in Table 7. These parameters were selected based on previous studies and by examining the mannequin and table cases. The beam angle of the luminaire was set at 20°, 30°, and wall washer (Fig. 11). A narrow beam angle of 20° sheds light on the object in a small

Table 6 Vertical illuminance values for table (a) Background illuminance ratio 1:5


Key light 10° Fill light 20° Back light 20°

1 : 1: 0 75 lx 75 lx —

3 : 1 : 0 75 lx 25 lx —

6 : 1 : 0 75 lx 15 lx* —

1 : 1 : 1 75 lx 75 lx 75 lx**

The ratio of lighting fixtures illuminance (Key light : Fill light : Back light)

3 : 1 : 1 75 lx 25 lx 25 lx** *: 15 was used instead of 12.5 because the minimum value was set to 15 lx. **: measured at the back center of the product (b) Background illuminance ratio 1:10


Key light 10° Fill light 20° Back light 20°

1 : 1 : 0 150 lx 150 lx —

3 : 1 : 0 150 lx 50 lx —

6 : 1 : 0 150 lx 25 lx —

1 : 1 : 1 150 lx 150 lx 150 lx**

The ratio of lighting fixtures illuminance (Key light : Fill light : Back light)

3 : 1 : 1 150 lx 50 lx 50 lx** **: measured at the back center of the product

Fig. 10 Outline of the hanger simulation


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Table 7 Simulation images for lighting variables of hanger

(a) Direct wall vertical illuminance 0 lx Color temperature

The beam angles of lighting fixtures 3000 K 4500 K

Spot 20°

Spot 30°

Wall washer

(b) Direct wall vertical illuminance 60 lx Color temperature

The beam angles of lighting fixtures 3000 K 4500 K

Spot 20°

Spot 30°

Wall washer

Fig. 11 Luminous intensity distribution curves of spot 20°, 30° and wall washer


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ellipse without overlapping of the light, and a wide beam angle of 30° forms overlapping light in a cone shape. A wall washer was used to shed uniform light on the entire wall so that the product and background wall were lighted to the same brightness.

Direct wall vertical illuminance refers to illuminance of the wall from the wall washer lighting without spot lightings. This illuminance was set as 0 lx for no lighting and 60 lx as about 1/3 of product illuminance in order to create a difference between wall lighting and product lighting. Since products are directed differently for hanger according to the difference in direct wall illuminance and product illuminance, direct wall illuminance was selected as a parameter. The direct wall vertical illuminance of 60 lx was created using a self-emittance function with a luminance value in the Lightscape 3.2. The vertical illuminance applied to this case was set to 150 lx excluding the direct wall vertical illuminance. The background illuminance was also created by uniform general lighting over the space, and its values was set 15 lx as same in the cases of mannequin and table lightings. The same color temperatures were used for mannequin and table. Table 8 shows illuminance values used for hanger lighting was measured at the centre of the cloth on the centre of the wall.

Table 8 Vertical illuminance and luminous flux of luminaires

Beam angles of luminaires Vertical illuminance Luminous flux

Spot 20° 150 lx 240 lm

Spot 30° 150 lx 500 lm

Wall washer 150 lx 110 lm

4 Results of subjective evaluation

The sum of scores was calculated for each simulation image to show the lighting design options of the image that received the highest score, and the subjective evaluation for each parameter was analysed. The results from twenty subjects were analysed together because the results from ordinary people and people with expert lighting knowledge were not significantly different. Table 9 shows chi-square test results.

Table 9 Chi-square test results (ordinary group and expert group)

Fashion item Evaluation factor Mannequin Table Hanger

Preference Χ2 = 18.59, d.f.= 23, p = 0.7246

Χ2 = 6.53, d.f.= 21, p = 0.9989

Χ2 = 6.67, d.f.= 11,p = 0.9996

Visual attention

Χ2 = 15.19, d.f.= 23, p = 0.8878

Χ2 = 11.96, d.f.= 21, p = 0.9406

Χ2 = 6.89, d.f.= 11,p = 0.9995

Perceptual clarity

Χ2 = 9.04, d.f.= 23, p = 0.9958

Χ2 = 8.29, d.f.= 21, p = 0.9938

Χ2 = 6.00, d.f.= 11,p = 0.9999

*p<0.05, *Χ2>d.f., Bold (*p and *Χ2)

The chi-square test’s null hypothesis was “the ordinary group and the expert group’s the tendency of evaluation is independence from evaluation factors”. All columns and rows show that p-values were more than 0.05, and chi-square values were less than degree of freedom values. Therefore, the null hypothesis was true, namely the tendency of evaluation from the ordinary group and the expert group was not significantly different.

4.1 Analysis of the results

4.1.1 Preference of luminous environment

The simulation images ranked 1st through 3rd as a result of sum of scores in the tournament evaluation on the preference of the luminous environment for mannequin, table and hanger are as shown in Table 10.

For the mannequins, the beam angle of the luminaires and color temperature did not show any tendencies in the differences in the results. In contrast, the illuminance ratio for the luminaires and background illuminance ratio showed distinct tendencies. Of illuminance ratios of 1:1, 3:1 and 6:1 for the luminaires, 3:1 and 6:1 were preferred, which implies that lighting that emphasises the 3D impression using shade is preferred. Of background illuminance ratios of 1:5 and 1:10, 1:10 was preferred. Therefore, subjects preferred the luminous environment that widely and intensely illuminated mannequin, forming a 3D impression using shade and creating a vivid atmosphere.

As for the evaluation of table cases, there was no significant difference in color temperature. On the contrary, among illuminance ratios of 1:1:0, 3:1:0, 6:1:0, 1:1:1 and 3:1:1 for the luminaires, 1:1:0 and 1:1:1 were highly preferred. Among background illuminance ratios of 1:5 and 1:10, 1:10 was preferred. Therefore, subjects preferred the table of luminous environment that uniformly and intensely illuminates the entire product without shade, creating large contrast with the background.

As for the evaluation of hanger cases, among beam angles of 20°, 30° and wall washer, 20° and 30° showed high preference. Among color temperatures of 3000 K and 4500 K, 3000 K showed high preference. For direct wall illuminance, 0 lx obtained high preference between 0 lx and 60 lx. Therefore, subjects preferred the hanger of luminous environment that intensely illuminates the product and forms a warm atmosphere.

4.1.2 Perceptual clarity of luminous environment

The simulation images ranked 1st through 3rd as a result of sum of scores in the tournament evaluation for perceptual clarity of the luminous environment for mannequins, tables and hangers are as shown in Table 11.


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Table 10 Preference rank of luminous environment

Rank

Subject 1st 2nd 3rd

Mannequin (background illuminance ratio– beam angles– illuminance ratio– color temperature)

(1:10–10/30–3:1–4500)

(1:10–10/30–3:1–3000)

(1:10–20/30–6:1–3000)

Table (background illuminance ratio– illuminance ratio– color temperature)

(1:10–1:1:0–3000)

(1:10–1:1:1–3000)

(1:10–1:1:1–4500)

Hanger (direct wall illuminance– beam angle– color temperature)

(0–30–3000)

(60–20–3000)

(0–20–3000)

Table 11 Perceptual clarity rank of luminous environment

Rank

Subject 1st 2nd 3rd

Mannequin (background illuminance ratio– beam angles– illuminance ratio– color temperature)

(1:10–20/30–6:1–3000)

(1:10–10/30–3:1–3000)

(1:10–20/30–6:1–4500)


(1:10–1:1:0–3000)

(1:10–3:1:1–4500)

(1:10–1:1:1–3000)


(0–30–3000)

(0–30–4500)

(0–20–4500)


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For the mannequins, wide angles of 20° for key light and 30° for fill light showed high scores. For color temperature, 3000 K obtained high scores. Among illuminance ratios of 1:1, 3:1 and 6:1 for the luminaires, 6:1 showed high scores. Among background illuminance ratios of 1:5 and 1:10, 1:10 showed a tendency for high scores. Therefore, subjects clearly perceived mannequin in the luminous environment that widely and intensely illuminates mannequin, forming 3D impression with large shade and creating warm atmosphere.

For tables, the color temperature did not show any significant tendencies. In contrast, of illuminance ratios of 1:1:0, 3:1:0, 6:1:0, 1:1:1 and 3:1:1 for the luminaires, 1:1:0 and 1:1:1 had high scores. Of background illuminance ratios of 1:5 and 1:10, 1:10 had high scores. Therefore, subjects clearly perceived tables under luminous environment that intensely and uniformly illuminated the product and created a warm atmosphere.

For hangers, of beam angles of 20°, 30° and wall washer, 30° had high scores, but the color temperature did not show a significant difference and direct wall illuminance of 0 lx had high scores between 0 lx and 60 lx. Therefore, subjects clearly perceived hangers under luminous environment that intensely illuminated the product using a wide light angle.

4.1.3 Visual attention of luminous environment

The simulation images ranked 1st through 3rd as a result

of sum of scores in the tournament evaluation for visual attention of the luminous environment for mannequins, tables and hangers are shown in Table 12.

For mannequins, wide beam angles of 20° for the key light and 30° for the fill light had high scores. Although the color temperature of 4500 K, which provided a cold and vivid atmosphere, had a high score, the difference in the scores between 3000 and 4500 K was insignificant. In contrast, of illuminance ratios of 1:1, 3:1 and 6:1 for the luminaires, 6:1 and 3:1 had a tendency toward higher scores. Of background illuminance ratios of 1:5 and 1:10, 1:10 had high scores. Therefore, a wide and intense light that formed a 3D impression of the mannequin using shade and created a cool and clean atmosphere effectively drew the attention of subjects.

For tables, although a color temperature of 3000 K, which provided a warm atmosphere, generally had higher scores than 4500 K, this was not a significant tendency. On the contrary, of illuminance ratios of 1:1:0, 3:1:0, 6:1:0, 1:1:1 and 3:1:1 for the luminaires, 1:1:0 and 1:1:1 had high scores. Of background illuminance ratios of 1:5 and 1:10, 1:10 showed a tendency towards higher scores. Therefore, an intense and uniform light that illuminated the product and created a warm atmosphere effectively drew the attention of subjects. This result is similar to that for the perceptual clarity of the luminous environment.

Table 12 Visual attention rank of luminous environment

Rank

Subject 1st 2nd 3rd

Mannequin

(background illuminance ratio– beam angles– illuminance ratio– color temperature)

(1:10–10/30–3:1–4500)

(1:10–10/30–3:1–3000)

(1:5–20/30–6:1–3000)


(1:10–1:1:0–3000)

(1:10–1:1:1–3000)

(1:10–1:1:0–4500)


(0–30–4500)

(0–20–4500)

(0–30–3000)


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For hangers, of beam angles of 20°, 30° and wall washer, 30° and 20° showed a tendency toward higher scores. Although 3000 K had high scores of color temperatures of 3000 and 4500 K, the difference in the scores was not significant. A direct wall illuminance of 0 lx had high scores between 0 and 60 lx. Therefore, an intense light that illuminated the product and created a contrast with the wall effectively drew the attention of subjects.

4.1.4 Statistical analysis

The chi-square tests were implemented to analyse what lighting factors influenced preference, visual attention and perceptual clarity. Table 13 shows chi-square test results of the mannequin case. Preference was influenced by the ratio of lighting fixtures illuminance, and background illuminance ratio. Visual attention was influenced by all lighting factors except the beam angles of lighting fixtures. In addition,

perceptual clarity was influenced by the ratio of lighting fixtures illuminance, and background illuminance ratio similar to the preference case. The ratio of lighting fixtures illuminance, and background illuminance ratio were more important factors than color temperature, and the beam angles of lighting fixtures did not affect all evaluation factors in the mannequin case.

Table 14 shows chi-square test results of the table case. Preference was influenced by color temperature and background illuminance ratio. Visual attention was influenced by all lighting factors while perceptual clarity was influenced by the ratio of lighting fixtures illuminance, and background illuminance ratio. The background illuminance ratio was most important factor in the table case because it affected all evaluation factors.

Table 15 shows chi-square test results of the hanger case. The preference was influenced by color temperature and wall

Table 13 Chi-square test results (mannequin)

Evaluation factor

Lighting factor Preference Visual attention Perceptual clarity

Color temperature *Χ2 = 1.11, d.f.= 1, p = 0.2918

*Χ2 = 4.44, d.f.= 1, *p = 0.0350

Χ2 = 0.71, d.f.= 1, p = 0.3991

Ratio of lighting fixtures illuminance *Χ2 = 8.87, d.f.= 2, *p = 0.0119

*Χ2 = 7.40, d.f.= 2, *p = 0.0247

*Χ2 = 13.87, d.f.= 2, *p = 0.0010

Background illuminance ratio *Χ2 = 32.4, d.f.= 1, *p = 1.25E−08

*Χ2 = 16.0, d.f.= 1, *p = 6.19E−05

*Χ2 = 45.5, d.f.= 1, *p = 1.52E−11

The beam angles of lighting fixtures Χ2 = 0.04, d.f.= 1, p = 0.8330

Χ2 = 0.4, d.f.= 1, p = 0.5271

Χ2 = 0.04, d.f.= 1, p = 0.8330

*p<0.05, *Χ2>d.f., Bold (*p and *Χ2)

Table 14 Chi-square test results (table)

Evaluation factor Lighting factor Preference Visual attention Perceptual clarity

Color temperature *Χ2 = 6.60, d.f.= 1, *p = 0.0102

*Χ2 = 5.55, d.f.= 1, *p = 0.0185

*Χ2 = 3.71, d.f.= 1, p = 0.0540

The ratio of lighting fixtures illuminance Χ2 = 2.54, d.f.= 4, p = 0.6378

*Χ2 = 15.58, d.f.= 4, *p = 0.0036

*Χ2 = 25.71, d.f.= 4, *p = 3.61E−05

Background illuminance ratio *Χ2 = 25.62, d.f.= 1, *p = 4.15E−07

*Χ2 = 43.12, d.f.= 1, *p = 5.15E−11

*Χ2 = 65.15, d.f.= 1, *p = 6.95E−16

*p<0.05, *Χ2>d.f., Bold (*p and *Χ2)

Table 15 Chi-square test results (hanger)

Evaluation factor

Lighting factor Preference Visual attention Perceptual clarity

Color temperature *Χ2 = 12.80, d.f.= 1, *p = 0.0003

Χ2 = 0.36, d.f.= 1, p = 0.5510

Χ2 = 0.09, d.f.= 1, p = 0.7656

The beam angles of luminaires *Χ2 = 3.33, d.f.= 2, p = 0.1889

*Χ2 = 2.53, d.f.= 2, p = 0.2818

*Χ2 = 6.53, d.f.= 2, *p = 0.0381

Wall illuminance *Χ2 = 8.89, d.f.= 1, *p = 0.0029

*Χ2 = 17.42, d.f.= 1, *p = 2.99E−05

*Χ2 = 15.02, d.f.= 1, *p = 0.0001

*p<0.05, *Χ2>d.f., Bold (*p and *Χ2)


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illuminance. Visual attention was influenced by only wall illuminance. While perceptual clarity was influenced by the beam angles of luminaires and wall illuminance. The wall illuminance was most important factor in the hanger case.

Overall, preference and visual attention was influenced by lighting factors related to color and contrast whereas perceptual clarity was more influenced by contrast than color. The difference between 10° to 30° of beam was not an important factor to light fashion items.

4.2 Summary of the results

The overall assessment for mannequins, tables and hangers based on the results of the subjective evaluation are summarised in Table 16.

As a result of mannequin evaluation, the results for visual attention and preference of the luminous environment were similar. First, to embody a lighting environment for fashion shops that attracts visual attention of consumers and show their preference, it is effective to use background illuminance ratio of 1:10, color temperature of 4500 K, illuminance ratio of 3:1 for the luminaires, and beam angles of 20° for key light and 30° for fill light. Using a luminaire that widely and intensely illuminates mannequin, forms 3D impression using shade, and creates a vivid and cool light attracts visual attention of consumers and reflects their preference. In addition, to embody a luminous environment for perceptual clarity of sculptures such as mannequin, it is effective to use background illuminance ratio of 1:10, color temperature of 3000 K, illuminance ratio of 6:1 for the luminaires, and beam angles of 20° for key light and 30° for fill light. The lighting plan that widely and intensely illuminates mannequin and is identical to the lighting plan for visual attention and preference, but it is more effective

to use a light source with a warm color temperature to increase perceptual clarity of the product.

The results for visual attention, preference, and perceptual clarity of the luminous environment were similar in the results of table evaluation. Such luminous environment appropriate for table lighting has background illuminance ratio of 1:10 and color temperature of 3000 K. As shown in the results above, subjective evaluation on preference of table lighting showed that it is effective to use uniform illuminance ratio for the luminaires. It is desirable for products on table to direct a luminaire that widely and intensely illuminates the product using low color temperature to create a warm and mild atmosphere. Background illuminance ratio was selected as 1:10 as in the results for mannequin. The luminous environment that creates a contrast with the background is effective for attracting visual attention and increasing perceptual clarity of the product. Shading is not a luminous environment for table to attract visual attention or increase perceptual clarity of the product.

Lastly, in the results of hanger evaluation, the results for visual attention, preference, and perceptual clarity of the luminous environment showed similar results. When such luminous environment is established for hanger, it is effective to design the environment with beam angle of 20°, color temperature of 3000 K, and direct wall illuminance of 0 lx. Also, visual attention and preference can be increased by avoiding installation of separate lighting on the wall other than the light that illuminates the product. On the contrary, the luminous environment with color temperature of 4500 K, direct wall illuminance of 0 lx, and wall washer was inappropriate for setting hanger lighting. Careful consideration is required for the lighting design since the user of wall washer can create uniform light on the wall and make consumers feel uncomfortable.

Table 16 Lighting design guideline

Guideline

Preference Visual attention

Background illuminance ratio: 1:10 Color temperature: 4500 K Ratio of lighting fixtures illuminance: 3:1 Beam angles of lighting fixtures: key light 20°, fill light 30°

Mannequin

Perceptual clarity Color temperature: 3000 K Ratio of lighting fixtures illuminance: 6:1 Beam angles of lighting fixtures: key light 20°, fill light 30°

Table Preference Visual attention Perceptual clarity

Background illuminance ratio: 1:10 Color Temperature: 3000 K Ratio of luminaire illuminance: 1:1:0, 1:1:1

Hanger Preference Visual attention Perceptual clarity

Beam angles of lighting fixtures: 20° Color temperature: 3000 K Wall illumination: 0 lx


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5 Conclusions

In this study, a subjective evaluation was performed using simulation images to evaluate the application of museum display lighting in a fashion shop. Display methods for mannequins, tables and hangers were evaluated. Sculpture display lighting as used in museums was used for mannequins and tables, and flat display lighting as used in museums was used for hangers.

The results of the subjective evaluation can be explained in terms of common and contrasting results. The common results indicated that lighting that provided a large contrast with the background was preferred for mannequins, tables and hangers. Although a background illuminance ratio of 1:5 is generally used in museums, in the subjective evaluation, subjects preferred a background illuminance ratio of 1:10 in all evaluations. Fashion shops were found to require a higher background illuminance ratio than museums.

Contrasting results were also found in the subjective evaluation of mannequins, tables and hangers due to the differences in the display method of the products to be illuminated. Mannequins are mainly displayed at the entrance of fashion shops to attract the visual attention of consumers and are illuminated to emphasise the visual clarity. Therefore, it is important to increase the visual clarity using shade by increasing the illuminance ratio for the luminaires. In contrast, a table is a display method for which consumers are likely to change the position of products as they touch and view them. Thus, a luminous environment that minimises the difference in illuminance between the luminaires and increases the background illuminance ratio providing increased perceptual clarity for the product is required. In addition, a light source with a warm and mild atmosphere helps consumers to thoroughly examine a product displayed on a table. Unlike mannequin and table displays, hangers display products on a wall and show a greater effect from light reflected by the wall. Therefore, careful consideration is necessary when using a device that illuminates the entire wall surface, such as a wall washer. It is also desirable to avoid a light source with a high color temperature and to create warm and mild luminous environment.

This paper presented a guideline on the application of museum display lighting in fashion shops. Such guidelines can be selectively applied according to the display environment and conditions in a fashion shop, thus promoting efficient product display and improvement of the accuracy of consumer choice. The results of this study are also applicable to the realistic and vivid display of products in apparel shopping malls on-line.

To emphasise the effects of display beam lighting in this study, the level of the ambient lighting was low and some vertical illuminance levels were also low. Thus, the lighting

simulation images have excessive limitations compared to actual lighting; thus, an additional experiment is required to evaluate preferences under actual display conditions. This study was also limited in that only particular colors and seasonal products were selected and evaluated in the simulated images and color appearance of simulated images could be different compared to that of the actual materials. In addition, a general lighting option and daylighting were excluded to simplify design variables. Further study is necessary to determine realistic costs and operational difficulties caused by an increase in the number of lights, and should perform subjective evaluation for all display methods such as tables, hangers and mannequins at the same time including a real surrounding environment situation.

Acknowledgements

This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIP) (No. 20150274).

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