Sunlight and LED Hybrid Illumination in Indoor Lighting
Design
Wen-Shing Sun*, Chih-Hsuan Tsuei
Department of Optics and Photonics, National Central University, Chungli, Taiwan
*wssun@https://www.doczj.com/doc/6c1946888.html,.tw
Abstract: We design a light integrating collector that can collect the sunlight and LED light to illuminate the
indoor spaces uniformly, and then use in simulating the sunlight/LED hybrid illumination at daytime, LED
lighting at nighttime.
?2010 Optical Society of America
OCIS codes: (080.0080) Geometry optics; (080.2740) Geometric optical design; (110.2945) Illumination design;
(150.2950) Illumination.
1. Introduction
As the efficiency of LEDs has been improved, the development of LED techniques shows that traditional illuminating light sources will be replaced gradually. In recent years, the LED efficiency value has exceeded 100 lm/W, which is better than that of mercury lamps [1, 2]. The LED illumination is applied such as street light, automobile, indoor lighting, and so on. LED will become the major lighting source [3, 4]. It is also well known that the sunlight can be used for illumination, its illuminated efficiency is even better than some of LED [5]. In this study, we present our simulations between LED and the sunlight/LED hybrid illuminating system and compare them with each other.
2. Theory
The concept of this study combined the optical design of sunlight concentrator and LED illumination. We design the sunlight concentrator, light integrating collector, LED reflector to provide a uniform and economical illumination.
2.1. Light-Emitting Diodes, LEDs
We simulate the performance of Nichia NS6W183T with 215 lm at 700mA forward current and 2.8V forward voltage, and its efficiency value is equal to 109.69 lm/W. We can obtain the detail database from Nichia website [6].
2.2. Sunlight
On Earth, sunlight has a luminous of about 100,000 to 120,000 lux at noon. Take the average illuminance at October 2009 for example, the illuminance values measured in Taipei, Taiwan, are as shown in Table 1, which the sunrise and sunset time are 6:00 in the morning and 5:00 in the evening.
In our study, we designed a sunlight tracking concentrator to collect the direct sunlight into our interior space, and we simulated our working time illumination from a.m.8 to p.m.9. According to the data meaning by Central Weather Bureau [7], Taiwan, it has average of 200 sunny days a year in Taipei. If we used these 200 sunny days well, we can save more power consumption and electricity charge.
Table.1 Average illuminance value measured at October 2009, in Taipei, Taiwan.
2.3. Sunlight concentrator and Light integrating collector
Sunlight Concentrator, as shown in Fig.1(a), use parabolic and ellipsoid mirror surface to focus a large area of sunlight onto the light guide. Sun tracking concentrators introduce beams of sunlight through holes into the roof. The collected beam can be relayed throughout the building by means of light guides or fibers [8].
The light integrating collector which shown in Fig.1(b) can collect and uniform sunlight and LED light. The light integrating collector with six cones below the top ceiling diffusing the light which emitted from light guides or
fibers. LEDs, which separated around the 4BaSO surface of the collector, emitting the light into the collector to
enhance the illuminance of target plan when sunlight is getting weaker. The 4BaSO is applied on the surface of the
collector in order to diffuse the light uniformly in lambertian type [9].
Fig. 1. (a) Structure of sunlight collector, and (b) light integrating collector above our laboratory. 3. Experiment and Results
We first produced LED light model, sunlight concentrator, light integrating collector and sunlight light model by LightTools software. Suppose the measured illuminance values of sunny days during half of a year is followed the value in Table.1, these two different light source models served as the basis for the 8.8m long, 2.94m wide, 2.8m high laboratory scale model [10]. For simulating the standard illuminance 500~750 lux on the table plane in our laboratory [10, 11], we calculated the power produced by these light sources and compared the results with each
other.
Fig. 2. Illuminance distribution on the table plane illuminated by 140 LEDs separate around the 4BaSO surface of the light integrating collector with parabolic reflector design. We obtained an average of 509.69 lux on the table plane.
After building the light sources models and our laboratory scale model, we simulated and calculated the illuminance and efficiency of these two different light sources illumination systems, respectively. We first used 140 LEDs separating around the 4BaSO surface of the light integrating collector, and simulated the illuminance on the
table plane, then we got average of 509.69 lux on the whole table plane, which shown in Fig.2. It means we need 140 LEDs to illuminate the table plane above the standard 500 lux when there is no light outdoor.
According to the illuminance value in Table.1, we need 140 LEDs to reach average 516.46 lux on table plan at 6:00 a.m., 100 LEDs on average 517.876 lux at 7:00, 40 LEDs on average 522.923 lux at 8:00, and 16 LEDs on average 526.895 lux at 9:00. The sufficient sunlight for indoor lighting offering the average 522.248 lux, 569.727 lux, 550.732 lux, 522.248 lux and 522.248 lux from 10:00 a.m. to 2:00 p.m., respectively. We don't need any LED during these four hours ideally. After 2:00 a.m., we need 40 LEDs to reach average 513.41 lux on table plan at 3:00 a.m., 100 LEDs on average 536.698 lux at 4:00, 140 LEDs on average 511.51 lux at 5:00, which the values above are listed in Table.2.
Suppose the measured illuminance values of sunny days during half of a year is followed the value in Table.1 and the illuminance values on table plan which described above, we can also calculate and compare with the electricity charge of T8, T5 fluorescent tubes, and LEDs in the same standard on table plane during our working time illumination from a.m.8 to p.m.9, which listed in Table.3. When we simulate with T8 or T5 fluorescent tubes, we need 10 tubes, respectively, to reach the standard illuminance. In the case of T8 fluorescent tube consumption for lighting up the single tube is 40W and 20W electricity ballast consume [12]. Another case of T5 fluorescent tube consumption for lighting up the single tube is 28W and 4W electricity ballast consume. And the other case of LED consumption for lighting up the single LED is 1.96W. We can easily calculate the power consumption 1756.16W of
sunlight/LED hybrid illumination from table.2 for one day, and figure out the advantage using sunlight/LED hybrid illumination in our indoor lighting from Table.3.
Table.2. The average illuminance on table plane.
Table.3 Power consumption and electricity charge of different illumination.
By guiding the sunlight into our indoor spaces, we can obviously realize the power consumption reduced from T8 florescent tube case to sunlight/LED hybrid illumination case in the standard of the average illuminance. Suppose we have at least half of a year sunny days, we can easily calculate the saving power charge during a year in sunlight/LED hybrid illumination case.
4. Conclusions
In this study we analyzed an economical illumination method by guiding sunlight into our indoor space. We found that the sunlight/LED hybrid illumination do perform better than LED. We also presented a light integrating collector to collect sunlight and LED light to simultaneously make the illuminance more uniform. According to our calculating results of the examination of simulations, we are assured of the potential advantages of sunlight/LED hybrid illuminating system in the future. In addition, the LightTools software and the Matlab program allowed us to easily simulate the illuminance and calculate the average difference and cost. Finally, we pointed out the possibility of using sunlight/LED hybrid illumination designs for indoor illumination in the near future.
5.Acknowledge
This study was sponsored by the National Science Council with the contract number NSC 98-2221-E-021-MY3. 6. References
[1]H. Liu, “A Long-Term Energy Saving Analysis on LEDs General Lighting in China,” J. Light & Vis. Env., 33, pp.110-113 (2009).
[2]M. G. Craford, “High Power LEDs for Solid State Lighting,” J. Light & Vis. Env., 32, pp.58-62 (2008).
[3]Y. Mizutani and T. Taguchi, “The Concept of Fashion Design on the Basis of Color Coordination Using White LED Lighting,” J. Light &
Vis. Env., 32, pp.241-245 (2008).
[4]T. Komoda, N. Ide and J. Kido, “High Efficient OLEDs and Their Application to Lighting,” J. Light & Vis. Env., 32, pp.75-78 (2008).
[5]N. Yoshizawa, H. Suzuki and N. Hara: “Applying the Geodesic Dome to Daylight Simulation”, J. Light & Vis. Env. 32, pp.46-50 (2008).
[6]Nichia, "NS6w183T Datasheet,” https://www.doczj.com/doc/6c1946888.html,/specification/led_09/NS6W183T-H3-E.pdf”.
[7]Central Weather Bureau, Taiwan, “https://www.doczj.com/doc/6c1946888.html,.tw/”.
[8]J. Mohelnikova, “Evaluation of Indoor Illuminance from Light Guides,” J. Light & Vis. Env. 32, pp.20-26 (2008).
[9]R. L. Lucke, "Lambertian radiance and transmission of an integrating sphere," Appl. Opt. 46, 6966-6970 (2007).
[10] C. H. Tsuei, J. W. Pen, and W. S. Sun, "Simulating the illuminance and the efficiency of the LED and fluorescent lights used in indoor
lighting design," Opt. Express 16, 18692-18701 (2008).
[11]Intellectual Property Office, Taiwan, "https://www.doczj.com/doc/6c1946888.html,.tw/service/about/about_us/about_us_history.asp".
[12]T. Yorifuji, M. Sakai, T. Yasuda, A. Maehara, A. Okada, T. Gouriki and T. Mannami, “Light Source and Ballast Circuits,” J. Light & Vis.
Env. 31, pp.157-172 (2007).