The Influence of Elapsed Time on the Subjective Evaluation of Interior Lighting

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1 IJBSCHS Biomedical Soft Computing and Human Sciences, Vol.20, No.1, pp IJBSCHS Biomedical Soft Computing and Human Sciences, Vol.x,No.x,pp ) Original Article Copyright 1995 Biomedical Fuzzy Systems Association [Original article] Copyright 1995 Biomedical Fuzzy Systems Association (Accepted on ) (Accepted on 20xx.xx.xx) The Influence of Elapsed Time on the Subjective Evaluation of Interior Lighting Hiroshi TAKAHASHI* and Satoshi MISAWA** *Department of Electrical & Electronic Engineering, Kanagawa Institute of Technology **Department of Electrical Engineering, Shibaura Institute of Technology Abstract: The illuminance and color temperature of a light source affect the perceived impression of interior lighting. People generally prefer a low color temperature (i.e., warm colors) in interior spaces with low illuminance, and a high color temperature, (i.e., cool colors) in interior spaces with high illuminance. This phenomenon is expressed by the Kruithof curve, which describes the relation between the illuminance and color temperature of a light source. However, there are issues with the Kruithof curve. Therefore, the aim of this study was to clarify the influence of elapsed time on the subjective evaluation of interior lighting. Two different scale models were used in this study. The Semantic Differential (SD) method was used to evaluate the impressions of the subjects. Five pairs of words (comfortable/uncomfortable, warm/cool, preferred/unfavorable, natural color appearance/artificial color appearance, and calming/restless) were employed in this study. Each subject is assumed the activity of relaxing in the living room and evaluates orally in this experiment. The results show the perception of comfort with regard to the interior space tended to increase with elapsed time. Keywords Elapsed time, Illuminance, Color temperature, Subjective evaluation, Interior lighting. 1.Introduction The illuminance and color temperature of a light source affect the perceived impression of interior lighting. People generally prefer a low color temperature (i.e., warm colors) in interior spaces with low illuminance, and a high color temperature (i.e., cool colors) in interior spaces with high illuminance. This phenomenon is expressed by the Kruithof curve, which describes the relationship between the illuminance and color temperature of a light source1). Wake et al.2) have reported research results that support the use of Kruithof s data. However, there are issues with the Kruithof curve3), 4). Nakamura and Karasawa5) conducted a subjective evaluation for various daily living activities to clarify the relationship 1030 Shimo-ogino Atsugi, Kanagawa , Japan Phone: htakahashi@ele.kanagawa-it.ac.jp between illuminance, color temperature, and the preferred atmosphere. Their results revealed that when the living activity was getting together, the preferred lighting conditions were similar to the Kruithof curve, whereas when the living activity was relaxing, the preferred lighting conditions deviated slightly from the Kruithof curve. Oi et al.6) conducted a subjective experiment using scale models to clarify the preferred combinations of illuminance and color temperature for six daily activities in residential houses. Their results revealed that the Kruithof curve is not necessarily applicable for various settings in residential houses. In previous research, a subjective evaluation of the impression of the lighting environment formed immediately after entering a room was carried out, since this is the time when the strongest and most important impression is formed. However, due to chromatic adaptation, the human impression of the lighting environment is expected to change with time. If the manner in which such changes occur was understood, a more comfortable lighting envi- 1

2 Biomedical Biomedical Soft Soft Computing and and Human Human Sciences, Vol.x, Vol.20, No.x, No.1, (20xx) 2015 ronment could be designed. Kakitsuba et al. 7), 8), 9) conducted a subjective evaluation on preferred color temperatures combined with room air temperatures from psychological and physiological responses. Their results revealed that 7500 K was more preferred than 3000 K at 1500 lx in spring and summer and 3000 K was more preferred than 7500 K at 200 lx in winter. Ishida and Inoue10) conducted a subjective evaluation to investigate how the initial adaptation level and elapsed time affected the proper illuminance for relaxation. Their results revealed that the proper illuminance made by the subject after 32 minutes was different depending on whether the initial adaptation level was 20 lx or 150 lx, and the effect of the initial adaptation level was compatible with the elapsed time. Furthermore, the illuminance level for relaxation that was obtained in their research was lower than the results of other studies. However, the influence of elapsed time on the subjective evaluation of interior lighting is not clarified. Therefore, the aim of this study is to clarify the influence of elapsed time on the subjective evaluation of interior lighting. 2. Experiment 2.1 Experimental apparatus Figure 1 shows the experimental apparatus. Two different scale models were used in this study. The first was a standard room and the second was an evaluation room. Both models were constructed from white (N9.5) styrene boards and were 1/10 scale models (360 mm (W) 450 mm (D) 240 mm (H)) of a living room. A 60-mm-diameter round shape imitating a ceiling light was formed in the center of the ceiling and diffusion paper was used to diffuse the light from a metal halide lamp. Color filters were used to adjust the color temperature of the light source, and were combined so that the correlated color temperature had a deviation ( uv) of less than from the blackbody locus. A sofa and coffee table were placed in the evaluation room to properly convey the image of a living room. Figure 2 shows an example of the evaluation room. Fig. 1. Experimental apparatus Fig. 2. Example of the evaluation room(200lx-4200k) 2.2 Experimental conditions The Semantic Differential (SD) method was used to evaluate the impressions of the subjects. Five pairs of words (comfortable/uncomfortable, warm/cool, preferred/unfavorable, natural color appearance/artificial color appearance, and calming/restless) were employed in this study. Figure 3 shows the evaluation scale. Table 1 shows the experimental conditions. The subjects were seven males in their 20s. In this experiment, each subject was assumed to have been relaxing in the living room and verbally replied to the evaluation. Fig. 3. Evaluation scale 2

3 H. H. TAKAHASHI and and S. S. MISAWA: The Influence of Elapsed Time on on the the Subjective Evaluation Evaluation of Interior of Interior Lighting Lighting Tab. 1. Experimental conditions 2.3 Experimental procedure The experimental procedure was as follows: (1) The subject was given 5 minutes to adapt to the standard room. (2) The subject then observed the evaluation room for a specified period of time (0, 2, 4, 6, 8, and 10 minutes) and performed an evaluation. (3) The subject was allowed to adapt to the standard room again and then observed the evaluation room of the other lighting condition. (4) Steps (1) to (3) were repeated. 3.Results The results for one of the subjects included extreme values, which were considered as defective values. Therefore, the results were processed by using the average of the results for the remaining six subjects. Figure 4 shows the relationship between the elapsed time and the comfort evaluation score. For an illuminance of 200 lx, the color temperature has a tendency to increase with elapsed time, and converges around the score of 1.2, which shows that "the environment is slightly comfortable" after 10 minutes; however, there are significant differences in the comfort evaluation score at 0 minutes. It is thought that the effect of the difference in color temperature on comfort is smaller because the color adaptation level is high as the elapsed time increases. For 500 lx, a similar convergence tendency is not observed, but the color temperature does maintain a constant value after a few minutes. Although the evaluation score shows a tendency to increase with elapsed time, it is suggested that the influence of the difference in color temperature on comfort is larger than compared with that of the 200 lx case. The influence of color temperature on comfort is considered to be large for high values of illuminance, since the difference in the comfort evaluation score at 500 lx is larger than that at 200 lx after 0 minutes. Figure 5 shows the relationship between the elapsed time and warmth evaluation score. For 200 lx, the impression of warmth (color temperature: 2000 K and 2500 K) is almost constant with elapsed time. Although there is a tendency to gradually feel the warmth with elapsed time for a color temperature of 3000 K or more, the warmth evaluation score remains almost constant after 10 minutes. Moreover, the difference in the warmth evaluation score of each color temperature decreases with elapsed time. For 500 lx, the change in the impression of the warmth with elapsed time for all of the color temperature conditions is small. The impression of warmth is considered to have a great influence on the impression formed by the subject after entering the room, and therefore, the impression of the warmth of the interior space is considered to have a tendency as large as that for high illuminances and low color temperatures. Figure 6 shows the relationship between the elapsed time and preference evaluation score. The preference of the interior space according to each illuminance shows that the same tendency as that for comfort was observed. Figure 7 shows the relationship between the elapsed time and nature of the color appearance evaluation score. A similar tendency can be observed for the illuminances of 200 lx and 500 lx. There is no significant change for the nature of color appearance with elapsed time also at any color temperature, but the nature of color appearance is different depending on the color temperatures. Figure 8 shows the relationship between the elapsed time and calm evaluation score. For 200 lx, a tendency to feel calmer as time passes for all of the color temperature conditions is shown, and the difference in calmness for each color temperature is small. Although the same tendency is observed for 500 lx, the difference in calmness for each color temperature is large compared to that for 200 lx. Thus, it is considered that the influence of the composure of the interior space for high illuminances is large. Next, the relationship between the elapsed time and each evaluation score for each color temperature is discussed. Figure 9 shows the relationship between the elapsed time and comfort evaluation score for each color temperature that was a characteristic. In accordance with the elapsed time, the difference in the comfort evaluation score in terms of illuminance becomes small for low color temperatures (2000 K, 2500 K) and a high color tem- 3

4 Biomedical Biomedical Soft Soft Computing and and Human Human Sciences, Vol.x, Vol.20, No.x, No.1, (20xx) 2015 perature (6500 K). Conversely, the difference in the comfort evaluation score in terms of illuminance is large for color temperatures of K after 10 minutes. Therefore, it is considered that for lighting with a deep color, the influence of illuminance on comfort becomes small as time passes. In this study, "deep color lighting" was determined to be a color temperature of 2500 K or less and a color temperature of 6500 K. Fig. 4. Relationship between the elapsed time and the comfort evaluation score Fig. 5. Relationship between the elapsed time and warmth evaluation score Fig. 6. Relationship between the elapsed time and preference evaluation score Fig. 7. Relationship between the elapsed time and nature of the color appearance evaluation score 4

5 H. H. TAKAHASHI and and S. S. MISAWA: The Influence of Elapsed Time on on the the Subjective Evaluation Evaluation of Interior of Interior Lighting Lighting Fig. 8. Relationship between the elapsed time and calm evaluation score Fig. 9. Relationship between the elapsed time and comfort evaluation score for each color temperature 5

6 Biomedical Soft Soft Computing and Human Sciences, Vol.20, Vol.x, No.1, No.x 2015(20xx) 4. Discussion Here we compare the experimental results with the Kruithof curve referring to the method of Nakamura and Karasawa 3). The Kruithof curve describes the relationship between the illuminance and color temperature of a light source. The white area represents comfortable area, and the gray area represents uncomfortable area of the Kruithof curve. It describes the tendency that low color temperature is preferred in the case of low illuminance, and high color temperature is preferred in the case of high illuminance. Figure 10 shows such a comparison for 0 minutes and 10 minutes. The size of each circle represents the magnitude of the comfort. For 500 lx at any time, the size of the circles in the comfortable area is relatively larger than those in the uncomfortable area. This shows that the results are in fair agreement with the Kruithof curve. For 200 lx, there are only slight differences in the sizes of the circles between the comfortable area and uncomfortable area. This shows that the results differ from the Kruithof curve. The evaluation scores are slightly comfortable or more comfortable at 10 minutes for every color temperature. Moreover, the comfort evaluation scores are high for the uncomfortable area of the Kruithof curve, since the comfort evaluation scores increase as the chromatic adaptation progresses for both illuminance conditions. All of the comfort evaluation scores after 10 minutes are higher than those at 0 minutes. Fig. 10. Comparison with Kruithof curve 5. Conclusion The influence of the elapsed time on the subjective evaluation of interior lighting was investigated by conducting subjective evaluation tests with small-scale models. The results are summarized as follows: (1) The perception of comfort with regard to the interior space tended to increase with elapsed time. (2) The perception of warmth is strongly influenced by the initial impression of the subject, and this tendency is as large as that for high illuminances and low color temperatures. (3) All of the comfort evaluation scores after 10 minutes were higher than those at 0 minutes. When the interior lighting environment is evaluated, the perception of comfort can be evaluated close to the actual lighting environment after 10 minutes adaptation to the lighting environment. This adaptation leads to ensure comfort in the interior lighting environment. References [1] Kruithof A. A. Tubular Luminescence Lamps for General Illumination, Philips Technical Review 1941; 6: [2] Wake T, Kikuchi T, Takeichi K, Kasama M and Kamisasa H. The effect of illuminance, color temperature and color rendering index of light sources upon comfortable visual environments in the case of office, Journal of Light & Visual Environment 1977; 1(2): [3] Bodmann H. W. Quality of interior lighting based on luminance, Transactions of the IES. London 1967; 3(1):

7 H. H. TAKAHASHI and and S. S. MISAWA: The Influence of Elapsed Time on on the the Subjective Evaluation Evaluation of Interior of Interior Lighting Lighting [4] Nakamura H. Is Kruithof s curve right?, Journal of the Illuminating Engineering Institute of Japan 2001; 85(9): [5] Nakamura H and Karasawa Y. Relationship between Illuminance/Color Temperature and Preference of Atmosphere, Journal of the Illuminating Engineering Institute of Japan 1997; 81(8A): [6] Oi N, Kasao M and Takahashi H. The preference of the indoor illuminance and color temperature : Scale model experiment assuming daily activity, Journal of Environmental Engineering, Architectural Institute of Japan 2007; 614: [7] Kakitsuba N, Nakamura H, Inagaki T and Horikoshi T. Evaluation on preferred color temperatures combined with room air temperatures from psychological and physiological responses Part1 Seasonal change in preferred color temperatures at 1500 lx, Journal of Architecture, Planning and Environmental Engineering, Architectural Institute of Japan 2000; 528: [8] Kakitsuba N, Moyoshi M, Nakamura H, Inagaki T and Horikoshi T. Evaluation on preferred color temperatures combined with room air temperatures from psychological and physiological responses Part2 Seasonal change in preferred color temperatures at 200 lx, Journal of Architecture, Planning and Environmental Engineering, Architectural Institute of Japan 2000; 532: [9] Kakitsuba N, Muro K and Horikoshi T. Evaluation on preferred color temperatures combined with room air temperatures from psychological and physiological responses Part3 Seasonal change in preferred color temperatures at 1500 lx for women aged in 30 s and 40, Journal of Environmental Engineering, Architectural Institute of Japan 2003; 568: [10] Ishida K and Inoue Y. Study on brightness for relaxation Influence of initial adaptation level and elapsed time, Journal of the Illuminating Engineering Institute of Japan 2005; 89(8A): Hiroshi TAKAHASHI He received the Dr. degree of engineering from Shibaura Institute of Technology in He has worked as an associate prof. of dept. of electrical & electronic engineering, faculty of engineering at Kanagawa Institute of Technology. His present research interests include the visual psychology. He is a member of the Illuminating Engineering Institute of Japan, Japan Society of Kansei Engineering. Satoshi MISAWA He received the Bachelor s degree in electrical engineering from Shibaura Institute of Technology in He is working at SEIBU RAILWAY Co.,Ltd. 7