Design and Optimization of Dot Pattern in Illumination

Design and Optimization of Dot Pattern in Illumination Lightpipe of Natural Light Guiding System Zong-Yi Lee1, Yi-Yung Chen1, and Allen Jong-Woei Whang1, 2 1 2

Photonics System Simulation and Design Laboratory, Department of Electronic Engineering

Photonics System Simulation and Design Laboratory, Department of Electro-Optical Engineering National Taiwan University of Science and Technology #43, Sec. 4, Keelung Rd., Taipei, 106, Taiwan, R.O.C

ABSTRACT In recent years, the practicality and importance of the illumination with sunlight are getting more seriously concern in public. The reason is that natural light is non-polluting, energy-saving, and healthy in comparison with traditional light sources. Therefore, our research focuses on how to replace the artificial sources by natural light. A Natural Light Guiding System has collecting, transmitting, and lighting parts. For replacing the traditional sources, the lighting part should have similar characteristic, such as intensity distribution and geometric parameters, to artificial sources. In this paper, we design, simulate, and optimize illumination lightpipe with dot pattern to redistribute the collecting sunlight from Natural Light Guiding System. The lightpipe includes input, system, and output parts. In the input part, we design a coupler to improve the coupling efficiency with natural light. For optimizing the efficiency of the coupler, we evaluate the relationship between the distance that is from the fiber to the lightpipe and the coupled power. In the system part, the sunlight is locked by total internal reflection, TIR, so we design dot pattern to scatter the locked sunlight for uniform lighting. In the output part, a uniform illumination is our goal. For designing the percentage of the surface will be covered by dot pattern, we offer a design theory and simulate the efficiency. Keywords: Natural Light Guiding System, Illumination Lightpipe, Optimization, Dot Pattern, Coupler

1

INTRODUCTION

Because the non-polluting and energy-saving, many researches focus on the new source, LED, for replacing the traditional source [1, 2]. LED has many advantages to be a green lighting but it has the same weakness with the traditional Novel Optical Systems Design and Optimization XII, edited by R. John Koshel, G. Groot Gregory, Proc. of SPIE Vol. 7429, 74290A · © 2009 SPIE · CCC code: 0277-786X/09/$18 · doi: 10.1117/12.825434

Proc. of SPIE Vol. 7429 74290A-1

sources in the healthy issue. The best healthy source in the world is natural light that can reduce the morbidity of some seasonal disease [3]. A Natural Light Guiding System can collect sunlight, transmit the collected sunlight, and redistribute the transmitted sunlight to fit the request of illumination. Recently, some of the researches about the green energy focus on the system [4-6]. However, the most of the researches focus on how to improve the efficiency of the collecting part. In fact, the Natural Light Guiding System has same problem with LED in how to replace the traditional lighting. Because the lighting system is always mounted on the building, the new source should be designed to have the same geometric parameters and electronic characteristics with traditional source. Because people are used to the condition of the traditional lighting, the new source should be designed to have the same distribution of the intensity with traditional source. In this paper, we would like to design a lightpipe in the lighting part to replace the popular traditional lighting, fluorescent lamp.

2

NATURAL LIGHT GUIDING SYSTEM

The Natural Light Guiding System can be separated into three parts, collecting, transmitting, and lighting parts. The illustration of the system is shown in the Fig. 1. In the system structure, the input of the system is natural light, sunlight, and the output of the system is the illumination light.

Input

System

Natural Light

Output

Natural Light Guiding System Collecting Part

Transmitting Part

Illumination Lighting Part

Fig. 1 The illustration of the Natural Light Guiding System

2.1

Collecting Unit

In this research, we utilize a Natural Light Guiding System in which the collecting component is a static concentrator that is invented by Photonics System Simulation and Design Laboratory, PSSDL, of National Taiwan University of Science and Technology [6]. The collecting component is used to collect nature light, and the structure of the component is shown in the Fig.2.


Fig. 2 The structure of the collecting component in the Natural Light Guiding System

3

ILLUMINATION LIGHTPIPE

In this paper, we would like to design the lighting part of the Natural Light Guiding System. Because the goal of the design is replacing the traditional source in the same environment, we design a lightpipe to support our idea. The lightpipe can be divided into input, system, and output parts. In the input part, we design a coupler to improve the coupling efficiency with natural light. In the system part, the sunlight is locked by total internal reflection, TIR, so we design dot pattern to scatter the locked sunlight for uniform lighting.

3.1

Structure Parameters

We want the lightpipe have the same distribution of the intensity with traditional source, so the dimension of the lightpipe refer to Hitachi’s light tube-FML. Its diameter is about 16 mm, and its length is around 150 mm. The picture of Hitachi’s light tube is shown in the Fig.3.

Fig. 3 The Hitachi’s light tube-FML

In the simulation, we take a fiber with 10 mm diameter as source that will be plugged in the end of the lightpipe. Schematic diagrams of the components are shown in the Tab.1; the conditions of simulation are shown in the Tab.2; and the diagram of simulation is shown in the Fig.4.


Tab. 1 The schematic diagrams of the components

Name of Components

Diagram of Simulation

Lightpipe Coupler Lightpipe + Coupler (I) Lightpipe + Coupler (II) Fiber Fiber + Lightpipe + Coupler Ray Tracing

Tab.2 The simulation conditions of each component

Coupler

Units

Outer Diameter

16

mm

Inner Diameter

10

mm

Length

5

mm

Material

PMMA

-

Lightpipe

Units

Diameter

16

mm

Length

150

mm

Material

PMMA

-

Detector

Units

Size

200×300

mm2

Distance

300

mm


300 mm

Fig. 4 The simulation model (left) and the ray tracing (right)

This study purports the sunlight in the fiber that is from the collecting component can be coupled into the lightpipe completely, and then the sunlight will emit from the lightpipe uniformly to achieve the requirements of uniform illumination. However, when the sunlight is guided into the lightpipe that is not designed, the light will be locked in the lightpipe by TIR. Next, we design the dot pattern in the lightpipe to destroy TIR to make the light can radiate uniformly from the lightpipe.

3.2

Design of Input Part

The lightpipe can be separated into three parts, input, system, and output parts, to design. First, we discuss the input part of the lightpipe with a coupler. The coupler not only is as a holder of fiber but also guides sunlight into the lightpipe with the lowest loss. In order to guide the sunlight into the lightpipe with the lowest loss, we simulate and evaluate the relationship between the distance that is between the output surface of the fiber and the input surface of the lightpipe and the power at the end of the lightpipe. The diagram of the simulation is shown in the Fig.5, and the conditions are shown in the Tab.3. We do the simulations with the different distance that is between the output surface of the fiber and the input surface of the lightpipe: 1, 10-1, 10-2, 10-3、10-4, 10-5, 10-6, 10-7, 10-8, 10-9, and 10-10 mm. The results of simulations are shown in the Tab.4, and we draw the data into a histogram in the Fig.6.

Fig. 5 The diagram of the simulation about the input part


Tab. 3 The conditions of the coupler simulation

Source

Units

Total Power

10,000

lm

Number of Rays

100,000

Rays

Direction

Random Lambertian

-

Length of Fiber

15

mm

10

mm

Input Diameter of Fiber Coupler

Tab. 4 The simulation result of the coupler

Distance (mm) Integrated Power (lm)

Units

6663.788

10-1

8519.493

Outer Diameter

16

mm

10

-2

8995.137

Inner Diameter

10

mm

10-3

9100.188

Length

5

mm

10-4

8583.396

-5

8975.379

10-6

9097.457

10

-7

8524.412

-8

8956.258

Material

PMMA Lightpipe

10

Units

Diameter

16

mm

10

Length

150

mm

10-9

9094.629

-10

8519.493

System Material

PMMA Detector

Output

1

10

Units

Size

100×100

mm2

Distance

10

mm

Integrated Power (lm) 9500 9000 8500 8000 7500 7000 6500 1

10-1

10-2

10-3

10-4

10-5

10-6

10-7

10-8

10-9

Distance (mm)

Fig. 6 The distance vs. the integrated power in the simulation of the coupler


10-10

According to the Fig. 6, the highest efficiency is about 9100.188 / 10000 = 91% when the distance between the output surface of the fiber and the input surface of the lightpipe is 10-3 mm. In the best position of fiber, we can guide the collected sunlight into the lightpipe with the highest efficiency.

3.3

Design of System Part

In the system part, we consider how to emit the collected sunlight uniformly. Since the sunlight is guided into the lightpipe, most of the light will be locked by TIR. Only few number of the sunlight will radiate out the lightpipe. In order to radiate the sunlight out the lightpipe uniformly, we must destroy TIR gradually. We design several types of dot patterns on the surface of the lightpipe to compare the abilities about destroying TIR. In general, the designed dot pattern has two functions. First is to destroy TIR so the sunlight will radiate out the lightpipe. Second is to control the emitted energy of each area of the lightpipe to get uniform illumination. I

20%

100 %

20

II

25%

80 %

20

III

33%

60 %

20

IV

50%

40 %

20

V

100%

20 %

20

Fig. 7 The illustration of the method about how to design the dot pattern

The design theory is described as follows. For simplifying the design, we divide the illuminated area into five areas, as shown in the Fig. 7. In order to get the uniform illumination, the illuminated areas of I~V parts must have the same energy. If the total energy of the lightpipe is 100 lm, the energy in each illuminated area should have 20 lm. According to the assumption, the dot pattern should destroy the 20 % TIR to emit 20 lm for lighting the illuminated area in the area I. After the area I, there has 80 lm will reach the area II. The dot pattern in the area II should destroy the 25 % TIR to emit 20 lm, 80 lm × 25 %, for lighting the illuminated area. Base on the above concept, the abilities about destroying TIR in the area III to V should be 33 %, 50 %, and 100 %. The ability about destroying TIR in each area not only means the percentage of the total energy will be emitted but also means the percentage of the total area will be covered by dot pattern. According to above theory, we do the simulation about the dot patterns, as shown in the Fig. 8. The conditions of simulation are shown in the Tab. 5.


Fig. 8 The diagram of the simulation about the system part

According to the Fig.8, we can observe obviously that some rays radiate out the surface of the lightpipe after designed dot pattern. As we know, the shape of dot pattern will affect the uniformity of illumination. Therefore, we try to change the shape of dot pattern to get the optimum efficiency. Tab. 5 The conditions of the dot pattern simulation

Source

Units

Total Power

10,000

lm

Number of Rays

100,000

Rays

Direction

Random Lambertian

-

Length of Fiber

15

mm

10

mm

Input Diameter of Fiber Coupler

Units

Outer Diameter

16

mm

Inner Diameter

10

mm

Length

5

mm

Material

PMMA

-

Lightpipe System

Units

Diameter

16

mm

Length

150

mm

Material

PMMA

-

Detector Output

Units

Size

200×300

mm2

Distance

300

mm


In order to get the higher efficiency, this study simulates different shape of dot pattern that generate different illumination respectively. Different shapes of dot pattern refer to the proportion area theory, 20%, 25%, 33%, 50% and 100%. The results of simulations are shown in the Tab. 6. Tab. 6 The comparison of different dot pattern Type of the Dot Pattern

1

Irradiance

Without Design

Integrated Power (lm)

Efficiency

Uniformity

Not

95.8

0.958%

399.406

4%

Uniform

333.5607

3.3%

Uniform

650.3473

6.5%

Uniform

Uniform

Top 2 Side

Top 3 Side

Top 4 Side


4

CONCLUSION

In this study, we can get 91 % coupled efficiency by the designed coupler and the best position of fiber. And the design of dot pattern on surface of lightpipe can destroy TIR to make the sunlight can radiate out the lightpipe uniformly. In the future, we will focus on the design of dot pattern or microstructure on the lightpipe to improve the efficiency and uniformity.

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[2]

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[3]

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[4]

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[5]

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