Range of Acceptable Illuminance by LED Colors in Indoor Spaces

Transcription

1 Range of Acceptable Illuminance by LED Colors in Indoor Spaces - Focus on Occupants Comfort and Communications in Living Rooms - Taeyon Hwang 1, Dong Gi Lee 2*, Jeong Tai Kim 1 1 Department of Architectural Engineering, Kyung Hee University, Yongin , Korea 2 Department of Architecture, Graduate School of Engineering, The University of Tokyo, Tokyo , Japan * Corresponding author: Dong Gi Lee(hwang@khu.ac.kr) Abstract Existing studies mainly use white color for conventional fluorescent lamps and LED lights. It has been recently found that lighting colors affect visibility, brightness and glare, but studies on the effect of the lighting color of LED light source on occupants are still insufficient. Therefore, this study aims to evaluate the optimal illuminance of each lighting color of LED light sources that occupants in an indoor space feel appropriate for comfort and communication among the seven major lighting colors (Red, Green, Blue, Cyan, Magenta, Yellow, and White) of LED light sources. The findings of the research are as follows. The evaluation of optimum illuminance for LED lighting colors found that occupants felt the cyan LED light source as similar to white light source, and the relative brightness of green lighting color was measured higher. The evaluation of the permissible range of illuminance for LED lighting colors found that occupants felt relatively darker for red lighting colors, and the relative brightness of green lighting colors was higher. An experiment with subjects for LED lighting colors consisting of 19 patterns of 7 colors in the living room of a house found that the optimum illuminance for occupants comfort was 32[lx] ~119[lx]. The optimum illuminance of Led lighting colors for occupants communication was 107[lx] ~584[lx]. Keywords: LED, lighting colors, reasonable range of illuminance, permissible range of illuminance, occupants comfort and communication, purity of colors, living room Introduction With the recent development of lighting sources, the importance of LED lights is being spotlighted which have long life, energy saving, and space saving advantages. Since the commercialization of blue diodes, the three primary colors of light, i.e., Red, Green, and Blue, 491

2 have become prepared, and the diversity of lighting colors could be attained by the control of the brightness of each lighting color. Such technical development opened the possibility for replacing the conventional light sources based on a black-body radiation. Thus, in this situation where the LEDs are rapidly spreading, studies on LED lights will be critical for evaluation of light environment. Many existing studies on lighting colors focus on color temperature. Studies on body reaction to color temperature and brightness of light source showed that high color temperature causes excitement and blue light contracts the pupil [1-3]. Furthermore, studies on the relationship between color temperature and visibility found that cyan fluorescent lamp has high discrimination rate for the Landolt ring, and character legibility is high in a lighting environment of high color temperature rather than low color temperature. The reason for this appears to be that the blue lighting colors with high color temperature contract the pupil, thus effectively improving the discrimination of characters [4-5]. According to a study on the brightness of lighting colors, the green colors can increase the tolerance for glare because although they have high brightness, the do not cause glare [6]. Furthermore, in the lighting environment of a fluorescent lamp, red and yellow colors offer higher visibility, red colors offer better color identification, and the blue colors offer higher brightness [7-10]. On the other hand, in the LED lighting, blue is sensed as the brightest, and white and orange colors are good for color discrimination. The reason for this is that blue and green emit only frequencies of a narrow band in spectrum distribution, and are not favorable for color discrimination [11-13]. In the living room of a house, fluorescent lamps and LED lights do not show big difference in optimal illuminance and proper color temperature. In VDT (Visual Display Terminal) work, the difference in lighting colors has a greater effect on visual fatigue than the difference in spectrum distribution between fluorescent lamp and LED lighting [14]. Existing studies mainly use white color for conventional fluorescent lamps and LED lights. It has been recently found that lighting colors affect visibility [4-5, 7-10], brightness [3, 12, 15] and glare [6], but studies on the effect of the lighting color of LED light source on occupants are still insufficient. This study intended to evaluate the optimal illuminance of each lighting color of LED light sources that occupants in an indoor space feel appropriate for comfort and communication among the seven major lighting colors (Red, Green, Blue, Cyan, Magenta, Yellow, and White) of LED light sources. Outline of Experiments As shown in Figure 1, an apparatus with an LED light source at the top (910 mm 775 mm 820 mm) was fabricated, and model experiments were performed with the inside of the apparatus. The purpose of these experiments was to evaluate the lighting colors in an abstract space. Therefore, white kent paper with 85% or more whiteness was bent in a half circle and placed at the front of the view so that the subjects would feel no distance in the space when they see the inside of the model. Whiteness is a one-dimensional number indicating the 492

3 degree of white of the surface color. The formula for assessing the whiteness of surface color was created by CIE (Commission Internationale de l'eclairage). For the standard illuminant for assessment, CIE Standard Illuminant D65 is used. The outside of the experimental apparatus was made with mat black paper to prevent light reflection. The size of the observation window (hereinafter "window") for observing the lighting colors inside the experimental space from the outside was determined as 170 mm 60 mm (width height) not to affect the critical angle of color discrimination by subjects [6]. The height from bottom to the window center of the experimental apparatus was 280 mm, and the chair height of the subject was adjusted so that the height of the subject's eyes would be equal to this value. Furthermore, the distance between the subject's eyes and the window was set at 50 mm mm so that the LED light source at top of the experimental apparatus will not be directly within the view of the subject during the experiments. Fig. 1 Configuration of the experimental apparatus and a picture of subject during experiment The lighting colors of the LED light source used in the experiments were the three primary colors, i.e., Red, Green, and Blue, their complementary colors Yellow, Cyan, and Magenta, and White which is the standard lighting color. When the distance to the main wavelength color of the maximum purity emitted by each lighting color is divided into four parts, the purity of color becomes 25%, 50%, and 75%. Considering the result of a study that displeasure increases with purity, it was reasonable to use lighting colors of low purity values in this study [16]. Thus, when the main wavelength color of the maximum purity of each color emitted from the standard white lighting fixture was 100%, a total of 19 colors were chosen for these experiments including the lighting colors at the excitation purity of 20%, 40%, and 60% for the six colors plus white. The lighting colors in this paper are indicated as R(Red), G(Green), B(Blue), Y(Yellow), C(Cyan), and M(Magenta), and the purity of color as 20 (20% purity), 40 (40% purity), and 60 (60% purity). The 19 colors of the LED light used in these experiments are shown in the CIE 1931 xy chromaticity diagram in Figure

4 For illuminance, the horizontal illuminance and vertical illuminance were measured. The measurement points of the horizontal surface were above the bottom of the experimental apparatus, and the measurement points of the vertical surface were below the right-side plate. The xy chromacity value of each lighting color and the maximum ranges of the presented illuminance are shown in Tables 1 and 2, respectively % C40 C60 B60 G60 C20 B40 G40 B20 G20 W M20 M40 M60 Y60 Y40 Y20 R20 R40 R Fig. 2 Lighting colors plotted on the CIE 1931 xy chromaticity diagram Table 1. xy chromacity values of 19 lighting colors expressed by LED Purity of Colours (CIE 1931 xyz Colour Space) Lighting Purity 100% Purity 60% Purity 40% Purity 20% Colours x y x y x y x y Red Green Blue Cyan Magenta Yellow White Table 2. Average range of illuminance for each lighting color of LED installed in the experimental apparatus Lighting Colours Red Cyan Purity Range of Illuminance 20% 0[lx]~3070[lx] Lighting Colours Purity Range of Illuminance 20% 0[lx]~2640[lx] Lighting Colours Purity Range of Illuminance 20% 0[lx]~3420[lx] 40% 0[lx]~2370[lx] Green 40% 0[lx]~2340[lx] Blue 40% 0[lx]~3370[lx] 60% 0[lx]~1930[lx] 60% 0[lx]~2150[lx] 60% 0[lx]~2130[lx] 20% 0[lx]~3140[lx] 20% 0[lx]~3630[lx] 20% 0[lx]~3280[lx] 40% 0[lx]~3020[lx] Magenta 40% 0[lx]~3320[lx] Yellow 40% 0[lx]~3310[lx] 60% 0[lx]~2880[lx] 60% 0[lx]~2840[lx] 60% 0[lx]~3320[lx] White 100% 0[lx]~3150[lx] 494

5 The experiment with subjects for the lighting colors of the LED light source was conducted in the light environment laboratory on the basement of the T college building from October 11 to 29, 2010 for 22 students (13 males and 9 females) in 20s and 30s who have normal color vision. For the sequence of experiment, the subject was asked to adjust illuminance for each lighting color pattern so as to find the optimal illuminance and permissible illuminance of the LED light source that occupants in an indoor space feel appropriate for comfort and communication. For the experiment sequence, 19 patterns were randomly given and the average experiment time was 60 minutes. For each pattern, the experiment started in dark condition and progressed as follows (Figure 3): 1 Lighting control was performed to the optimum brightness (optimum illuminance) that the subject feel and then to the brightest condition. 2 Lighting control was performed to the optimal illuminance and then to the lower limit of the permissible range of brightness. 3 Lighting control was performed to the optimal illuminance again and then to the upper limit of the permissible range of brightness. 4 In this condition, lighting control was performed to the optimal illuminance. Answer the questions when each lighting color is finished (6 colors and white) Fig 3. Sequence of the experiment Results Experiment for Occupants Comfort The optimal illuminance and permissible range of illuminance of each lighting color of LED light sources that occupants in an indoor space feel appropriate for comfort were evaluated for the seven major lighting colors (Red, Green, Blue, Cyan, Magenta, Yellow, and White) of LED light sources. In the experiment, the lower and upper limits were measured once, and the optimal illuminance was measured three times. The results for optimal illuminance were analyzed using the average values. The optimal illuminance and permissible range of illuminance of each lighting color are shown in Table 3. For the lower limit of the permissible range of illuminance, the minimum illuminance was 25 [lx] of R60 and the maximum illuminance was 37 [lx] of G40. For the upper limit of the 495

6 permissible range of illuminance, the minimum illuminance was 102 [lx] of C20 and the maximum illuminance was 37 [lx] of G40. To compare the optimal illuminance and permissible range of illuminance of each lighting color, the ratio of the illuminance of each lighting color to the optimal illuminance of white which was set at 1 is shown in figure 4. The optimal illuminances of C20 and C40 were identical to that of white. The optimal illuminances of G40, G60, and Y60 showed a relatively high difference from that of white. It appears that the lighting colors presented in this study require higher illuminances than white. The evaluation of displeasure for LED lighting colors showed that the percentage of subjects who felt displeasure even at the optimal illuminance was the highest for R60, followed by G60, R40, G40, M60, and B60 (Table 3). According to the KS illuminance standards, the general working surface illuminance in the living room for comfort and relaxation was 30~40~60 [lx], which is similar to the experiment results for optimal illuminance in this study [17]. Table 3. Reasonable range of illuminance, permissible range of illuminance, and displeasure ratio for comfort of LED lighting colors Lighting Colours Permissible Range of Reasonable Range of Displeasure Ratio Illuminance [lx] Illuminance [lx] [%] R 20 31~132 40~99 5% R 40 26~118 35~84 68% R 60 25~112 32~86 95% G 20 30~133 42~92 5% G 40 37~166 46~119 68% G 60 33~147 47~107 77% B 20 28~120 38~90 0% B 40 30~126 39~95 23% B 60 27~117 37~88 59% C 20 26~102 32~75 0% C 40 27~104 34~81 18% C 60 31~116 43~83 45% M 20 28~132 40~88 5% M 40 30~133 44~94 18% M 60 31~133 45~93 64% Y 20 33~132 44~94 5% Y 40 32~140 45~102 9% Y 60 33~149 48~107 32% W 27~105 34~81 5% 496

7 백색 LED 적정조도와의비 Y60 Y40 Y20 M60 M40 M20 C60 C40 C20 B60 B40 B20 G60 G40 G20 R60 R40 R20 W Minimal Illuminance Optimal Illuminance Maximal Illuminance Fig. 4. Ratio of Optimal Illuminance to White LED Experiment for Occupants Communication The optimal illuminance and the permissible range of illuminance of Led light source that occupants feel appropriate for communication in indoor space were evaluated. In this experiment, the lower and upper limits were measured once, and the optimal illuminance was measured three times. The results for proper illuminance were analyzed using the average values. The proper illuminance and allowable illuminance range of each lighting color are shown in Table 4. For the lower limit of the permissible range of illuminance, the minimum illuminance was 89 [lx] of R60 and the maximum illuminance was 237 [lx] of G40. For the upper limit of the allowable range of illuminance, the minimum illuminance was 299 [lx] of C20 and the maximum illuminance was 653 [lx] of G40. To compare the optimal illuminance and permissible range of illuminance of each lighting color, the ratio of the illuminance of each lighting color to the optimal illuminance of white which was set at 1 is shown in figure 5. The optimal illuminance of C20 was identical to that of white and the optimal illuminances of other lighting colors were higher than that of white. In particular, the optimal illuminance was considerably high for green LED light sources, and it appears that the lighting colors presented in this study require higher illuminance than white. The evaluation of displeasure for LED lighting colors showed that the percentage of subjects who felt displeasure even at the optimal illuminance was the highest for R60, followed by M60, G60, G40, C60, and R40 (Table 4). According to the KS illuminance standards, the general working surface illuminance in the living room for communication was 150~200~300 [lx], which is similar to the experiment results for optimal illuminance in this study [17]. 497

8 Table 4. Reasonable range of illuminance, permissible range of illuminance, and displeasure ratio for communication of LED lighting colors Lighting Colours Permissible Range of Reasonable Range of Displeasure Ratio Illuminance [lx] Illuminance [lx] [%] R ~ ~289 5% R ~ ~281 55% R 60 89~ ~241 95% G ~ ~389 25% G ~ ~584 60% G ~ ~495 70% B ~ ~272 0% B ~ ~365 5% B ~ ~317 45% C 20 98~ ~250 5% C ~ ~282 15% C ~ ~300 60% M ~ ~318 10% M ~ ~258 15% M ~ ~341 80% Y ~ ~290 10% Y ~ ~332 0% Y ~ ~302 35% W 97~ ~242 5% 백색 LED 적정조도와의비 Y60 Y40 Y20 M60 M40 M20 C60 C40 C20 B60 B40 B20 G60 G40 G20 R60 R40 R20 W Minimal Illuminance Optimal Illuminance Maximal Illuminance Fig. 5. Ratio of Optimal Illuminance to White LED Conclusion This study intended to evaluate the proper illuminance of each lighting color of LED light sources that residents in an indoor space feel appropriate for comfort and communication among the seven major lighting colors (Red, Green, Blue, Cyan, Magenta, Yellow, and White) of LED light sources. 498

9 The findings of the research are as follows. 1. The evaluation of optimum illuminance for LED lighting colors found that occupants felt the cyan LED light source as similar to white light source, and the relative brightness of green lighting color was measured higher. This agrees with the results of the existing studies. 2. The evaluation of the permissible range of illuminance for LED lighting colors found that occupants felt relatively darker for red lighting colors, and the relative brightness of green lighting colors was higher. This agrees with the results of the existing studies. 3. An experiment with subjects for LED lighting colors consisting of 19 patterns of 7 colors in the living room of a house found that the optimum illuminance for occupants comfort was 32[lx] ~119[lx], which generally satisfies the KS illuminance standard 30[lx]~40[lx]~60[lx]. 4. The optimum illuminance of Led lighting colors for occupants communication was 107[lx] ~584[lx], which generally satisfies the KS illuminance standard 150[lx]~200[lx]~300[lx]. Acknowledgements This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (No ). References 1. Deguchi T, Sato M: The effect of color temperature of lighting sources on mental activity level: The Annals of Physiological Anthropology 1992; 11(1): Iwakiri K, Watanuki S, Yasukouchi A: The effect and after-effect of light-source color on early component of CNV: Proceedings of Japan Ergonomics Society 1997; 39: Yoon I, Horikoshi T, Miyamoto S: The effect of different colour temperature of fluorescent lamps on brightness perception: Journal of Architecture, Planning and Environmental Engineering 1996; 61(489): Navvab M: A comparison of visual performance under high and low color temperature fluorescent lamps: Proceedings of 2000 IESNA Annual Conference 2000; Berman SM, Fein G, Jewett DL, Ashford F: Luminance controlled pupil size affects landolt C task performance: Journal of the Illuminating Engineering Society 1993; 22(2): Hsieh M, Munakata J, Hirate K: Research on the Effect of Colored Lights on Evaluation and Range of Discomfort Glare: Journal of the Illuminating Engineering Institute of Japan 2005; 89(11):

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