Design of Lighting System for Energy Saving Based on Wsn

Journal of Information & Computational Science 8: 16 (2011) 3785–3799Available at http://www.joics.com

Design of the Lighting System for Energy Saving Based onWireless Sensor Network

Chunfeng FAN a, Shan JIN a, Yun MENG a, Weidan HONG b,Qingzhang CHEN a,∗

aCollege of Information Engineering, Ningbo Dahongying University, Ningbo 315175, ChinabCollege of Computer, Zhejiang University of Technology, Hangzhou 310023, China

Abstract

As the energy conservation and environmental protection take more and more attentions, energy savingis becoming increasingly vital. We can detect environment condition automatically through intelligentcontrol and adjust environment’s parameters according to the demands of people’s behavior so as tomeet people’s demand and save energy. This paper aims to construe a intelligent lighting energy savingsystem. In this paper, we use constructed intelligent lighting energy saving system, the hardware of whichadopt sensor network technology, and that can implement without destroying the original lighting system.Since it can not only reduces the cost of renovation, but also saves electricity. The system’s hardwareis composed of wireless sensor node module and lighting node module. As an important component thesystem software, Lighting control algorithm is the core of the whole system. After calculated the dimmingfactors, it can control the brightness of our lights through these factors. In the algorithm proposedconcepts such as dimming Zone Zdim, illumination lighting Zone Zlamp and coverage. Dimming ZoneZdim is circular area which takes user’s location as the center. The algorithm dimming the lights in thiszone. Experimental results show that the constructed system is effective and reliable. In the experiment,we arranged 9 lighting nodes and 16 wireless sensor nodes. Experiment show the effect of two cell detectedperson. The experiment verify correctness of the algorithm in small scale.

Keywords: WSN; Intelligent Control; Energy Saving; Interior Lighting

1 Introduction

Wireless sensor networks (WSN) is a combination of computing, communications and sensor tech-nology, has become an active field of computer science research branch now[1]. After the conceptof WSN proposed, it has a great development in application field. Sensor networks, also known asthe Internet of things, refers to the perception of the physical world for the purpose of informationprocessing as its main task, network information exchange carrier, to achieve things with objects,

∗Corresponding author.Email address: [email protected] (Qingzhang CHEN).

1548–7741/ Copyright © 2011 Binary Information PressDecember 2011

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3786 C. FAN et al. / Journal of Information & Computational Science 8: 16 (2011) 3785–3799

things and information exchange between the provision of perceptual information services, intel-ligent integrated information system. In addition to sensor nodes of the network, sensor networkscan also work with the Internet, mobile communication network and other networks to achievefull integration [2].

1.1 Background and significance

Since 1995, the country’s generating capacity of 1.0023 million kwh to 3.4268 trillion kwh ofelectricity consumption throughout the year 2008, the use of electricity has grown rapidly. Yetthe electricity for lighting has a considerable percentage, about 10-15%. In our country, theelectricity is made of coal, so the use of electricity is closely relative with environmental pollution.we use new type illuminant, high luminous efficiency, however, the lighting system is old and lowefficiency. So there is a great potential for energy saving[3].Nowadays, there are three kinds of intelligent lighting control techniques: cable control, power

line carrier(PLC) control and the radio frequency control. Each control methods has its ownadvantages and disadvantages. The cable control transmit reliably, but the installation is incon-venient. Because of the irregularity and the impact of random interference from the power linecarrier communications, the PLC is difficult to develop. The Radio frequency control transmitmay has some instability, but it is easy to install.We mostly used cable control in the Intelligent lighting systems now. In order to install the

Energy-saving system in the existing lighting systems, it must destroy the original lighting system,which not only affect the appearance, also Require a lot of renovation costs. In the paper, wedesign the energy-saving lighting system through WSN. According to the current light intensityand people’s location, the system automatically adjust environment’s parameters according to thedemands of people’s behavior so as to meet people’s demand and save energy. So it can overcomethe complex wiring, the high cost of reconstruction and so on.

1.2 Related research

In recent years, WSN in intelligent energy-saving lighting develops rapidly and a lot of relevantpapers issued. Several works [4-13] have investigated using WSN in light control for energyconversation. In [4] proposes a lighting control algorithm and the lighting devices are divided intotwo types — the whole lighting device and local lighting device. It propose two decision algorithmsto determine the properilluminations of devices and to achieve the desired optimizationgoals. Thesystem’s architecture is complex. The sensor networks is only used to detect the environment.The sink node collected the data and then Connect with the master controller through RS232.However, the master controller communicate with the whole lighting devices control server andthe Local control circuit separately via Ethernet and RS232. Whole lighting devices controlserver links to Whole lighting dimmers through the RS232. So the installation of such a systemis inconvenience. Papers [7] [8]and [11] introduce light control using wireless sensors to saveenergy for commercial buildings. A lighting control algorithm is proposed in [11], which is mainlydirected against the entire environment, and adjust all the lamps in it. If the the size of this roomis very large, the process of calculation is difficult. Papers [5] is mainly for media production,and it defines several kinds of user requirements and their corresponding cost functions. The goalis to adjust lights to minimize the total cost. In paper [13] designed a home lighting system for

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C. FAN et al. / Journal of Information & Computational Science 8: 16 (2011) 3785–3799 3787

energy-saving, but it only control the lights on or off, when the user carrying a wireless deviceRFD into the room lights in the region will open automatically.

1.3 Problem definition and technical means

Across the the above works’ analysis, we know that the systems are mainly used centralizedcalculation. The wireless sensor nodes detect environment condition automatically and acquirethe Light intensity, then send to the Sink nodes through the WSN. The sink node communicatewith the master controller through RS232. The factors of lights are calculated on the mastercontroller, and then send the factors to the lighting control node. The process of the implementforms a closed loop. But communication between the main controller and the lighting devices iswired. The process of work is shown in Fig. 1.

Fig. 1: The closed-loop device control procedure

For example, paper [11] proposed an intelligent lighting control algorithm, which mainly direct-ed against the entire environment, and adjust all the lamps in it. If the number of users in theenvironment small, such calculation is not necessary.Based on the above analysis,we know two shortcomings can be overcome. In our paper, we

design a distributed-computing and intelligent lighting control algorithm, which calculate thefactors of lights separately in every dimming zone.

1.4 Contributions

The purpose of this paper is to control the brightness of lamps through the calculated factorsof lights, so as to achieve the requirments of energy-saving. Main contents of this article are asfollows:1) discussing of the techniques existed, and combined with the advantages of wireless sensor

networks, we proposed an energy-saving lighting system based on WSN;2) proposed a lighting control algorithm based on WSN;3) Take the experimental environment, consist of wireless sensor nodes and lighting nodes.

Through the experimental, we verify correctness of the algorithm in small scale.


2 Lighting Control Algorithm

In the paper, we proposed an intelligent lighting control algorithm, which not only satisfy thepeople’s parameters also the requirements of energy-saving. Through the algorithm, systrm canturn on/off or adjust the lights automatically so as to achieve energy-saving .

2.1 Overview of algorithm

Ther is a room, with Length Rl and Width Rw. Fig. 2 shows the integration of ceiling and work-plane. The workplane is divided into m∗n regular grids, labeled as G11, · · · , G1n, · · · , Gm1, · · · ,Gmn. Each grid has a wireless sensor node. In the ceiling fixed k lamps. Each of them hasequipped with a lighting control node, named Ci.

Fig. 2: Integration of ceiling and workplane

The summarization of algorithm is as follows:1) After deployed, the location of node is fixed and store its own location information. Wireless

sensor nodes detect the environment whether someone enter and whether the lamps need toadjust. If need to adjust, the whole system is triggered;2) The wireless sensor node calculate the illuminance of the grids need to adjust, and then store

in the user-demanded illumination array. In the same time, the grids’ location information alsostore in an array of location information. They are all broadcasted to the lighting nodes;3) According to the array of location information, the lighting node calculate the illumination

of these grids. They are deposited into the single illumination array and then sent to the wirelesssensor nodes;4) In the wireless sensor nodes using two arrays calculated the factor of lights, which are then

returned to the lights node.The algorithm include initialization phase, generation of the user-demanded illumination array

E, the generation of the single illumination array Ai and calculation of infactor of lights d.

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2.2 Initialization

The main task of Initialization phase is as follows: to initializing the node location information,the user-demanded illumination Esat, the radius lsat of dimming area Zdim, and illuminationlighting zone Zlamp. After nodes deployed, the location of nodes are known. Esat and lsat aredecided by the architectural lighting designing standards, and the user’s preferences. The Zlamp

determined depending on the lamp we choosen.

2.3 The user-demanded illumination array E

Fig. 3: The location of the user

Fig. 4: The flow chart of L


As shown in Fig. 3, Zdim is an area to the user’s location as the center. We should calculate thedemanded illumination, and then store them in the user-demanded illumination array E. Firstly,we generate the user’s position array L(the length of the array lvector). At the same time, thegrids’ location information array H(the length of it 2lvector) is generated. The flow chart shownin Fig. 4.If nore than one users in the neighboring grids, some will be covered by multiple Zdim. It will

make some grids bright particularly. So we put forward the concept of coverage to address thissituation. As is shown in Fig. 5, s is the distance between the calculaten point and the grid userin. The coverage is: Dcover = 1− (2(lsat−s))

/√(Rw/m)2 + (Rl/m)2 .

Fig. 5: Multiple coverage

Now, we Transform L into E. Scaning the L and read out the value of L to calculate theillumination, and then deposit into the E. The flow chart of E shown in Fig. 6.

Fig. 6: The flow chart of E

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2.4 The single luminaire illumination array Ai

Each luminaire has illumination lighting zone. In order to calculate Ai, we should count theillumination the luminaire supplied. If the calculated point is not in Zlamp, the illumination affectis 0, otherwise is the calculated values. Fig. 7 Shows the lamps and grids in Zdim.

Fig. 7: The lamps and grids in Zdim

2.4.1 Illuminance calculation

In Fig. 8, the system detects the location of the user Q (x, y), point P(xi,yi) is the lamp’slocation. h is the height of lamp installation. According to the formula A = Iθ/l

2 = Iθ/h2×cos θ,

we first should compute cos θ.

Fig. 8: Integration of ceiling and workplane

s is the horizontal distance from the calculated point to lamp. s =√

(x− xi)2 + (y − yi)2, l =


√s2 + h2, so cos θ = h/l = h

/√(x− xi)2 + (y − yi)2 + h2 . Finally, we can calculate

A = Iθ/h[(x− xi)2 + (y − yi)2 + h2] . (1)

2.4.2 Calculation of Ai

After the lighting node receives H, taking outthe first two elements as Q(x, y), while the locationof Ci as P(xi,yi). First, check whether s is large than Zlamp, if yes, the the Ai will be set asillumination derived using the formula 1, or set 0. The flow chart of Ai shown in Fig. 9.

Fig. 9: The flow chart of Ai

2.5 The factor of lighting d

Through the above process, there has been user-demanded illumination array E and the singleillumination array Ai in the wireless sensor node. Suppose di is the factor of lamp i(i = 1 · · ·k).So, we can know that E.

E =k∑i=1

diAi =

k∑i=1

di{Ai[0], · · · , Ai[lvector]} (2)

Substitute the E and Ai into the Equation 2:

E =

A1[0] A2[0] · · · Ak[0]

· · · · · · · · · · · ·A1[lvector] A2[lvector] · · · Ak[lvector]

d = Ad (3)


The purpose of algorithm is saving energy, while the sum of factor d represents energy_saving.So we can transform into solving the following Linear Equations:

E = Ad

min‖d‖1 = min(|d1|+ · · ·+ |dk|)0 < di < 1

2.6 Adjustment of d

In Fig.10, users A, B, C enter the different grids at the same time. The wireless sensor nodescalculate the factors d and send them to lighting nodes Ci. Some can receive more than onefactors, such as C1(3), C2, C3 and C4(2). So we should adjust the factor d.We take the Maximum received factors, and then to control the lighting nodes.

Fig. 10: Three users in the different grids

Wireless sensor nodes send d to the lighting nodes Ci in Zdim. When Ci received d, it willtransform d into control signals to control dimming circuit.

3 Architecture of the System

3.1 The structure of the system

The system uses the ZigBee to build the wireless sensor network. The system including thelighting nodes deployed in the ceiling, the wireless sensor nodes arranged in the workplane, thecommunication protocol between the two kinds of nodes and the lighting control algorithms.There is a adjustable lamp in the lighting node. In order to adjust the lamp, the system should


chang the dimming signal. The wireless sensor nodes have two sensors. They use to detect thepeople and monitor the optical. They are implemented by infrared sensors and lighting intensitysensors separately.

3.2 Hardware of system

The system’s hardware includes WSN nodes design, sensor design and dimming control circuitdesign. WSN node used to process the information collected by sensors, Receive and send data,and calculate, and then to control the lighting control circuit. The overall system hardware blockdiagram shown in Fig. 11.

Fig. 11: The hardware block diagram

3.2.1 Wireless sensor nodes

Wireless sensor node mainly consists of two parts: the sensor and the CPU section. Because thelighting intensity sensor output is analog, in this node, A/D converter to convert this signal intoa luminance signal. Then compare it to Pre-set luminance.Sensors have the following two functions:(1) people detection: system detected the people through infrared sensors. If someone enter, it

will turn on the lights, or they will automatically turn off lights.(2) luminance detection: The lighting intensity sensors detects the room’s luminace. Compare

the measured values with the pre-set luminace, if they are not epual to each other, systemautomatically adjust the lights, so as to meet the required luminance.


3.2.2 Lighting nodes

The primary function of lighting nodes is transforming the lighting factors into the luminancelevel to adjust the lamps. The node including CPU part and the light intensity control section.In the paper, we use PT4115 chips as LED dimming driver, and choose the way of PWM

dimming. The PWM is a way that control the time LED light through the pulse durationratio to relize the energy_saving. The NE555 is PWM modulation which controled by X9241potentiometer can realize the pulse duration ratio at range of 64 levels in 0% to 100%. The LEDcontrol schematic diagram shown in Fig. 12. In the figure, X9421 is programmed to control theNE555’s pulse duration ratio output. And this signal goes to PT4115’s dim_port to control the1W LED.

Fig. 12: The LED control schematic diagram

3.3 Software of system

The software of system includes the lighting control algorithm and the node’s networking proto-cols. As follows:(1) the lighting control algorithm: since the system consists of two types of nodes, the software

in different type of nodes is not the same. In the second chapter we have described elaborately,it is the core of our system.(2) the communication between the two nodes using ZigBee protocol. It is widely used in low-

power short-distance transmission applications, especially those applications based on wirelesssensor network. In the paper, nodes using TI’s ZigBee protocol stack, which integrates theZigBee implementation from the physical layer to the network layer.


4 Algorithm Verification in the System

4.1 Experiment environment

According to the size of the room and a variety of factors, we distribution the lamps through theDIALux 4.7 lighting calculation software plug-in DIALux 4.7, and make sure the luminance ofthe room meet the requirements of architectural lighting design manual. The layout of the lampsas shown in Fig. 13. In the workplane, arranged 4*4 wireless sensor nodes. In the experiment,we deploy 9 lighting nodes and 16 wireless sensor nodes, also define a dimming zone Zdim, radiuslsat = 0.8m and illumination lighting zone of Zlamp = 0.6m.

Fig. 13: The layout of the lamps

4.2 Analysis of experimental results

More than one users enter the No. 7 and NO. 10 grids at the same time. In the experiment setthe No. 7 and NO. 10 wireless sensor nodes’ P0.1 as 1.In Fig. 14, users in No. 7 and NO. 10 grids at same time, through calculation, lamps D, E, G,

H in the zone Zdim1, and lamps B, C, E, F in the zone Zdim2. The result is shown in Fig. 5. Wealso measure the pulse duration ratio of E as shown in Fig. 16, the pulse duration ratio is 50%.

5 Conclution and Prospect

5.1 Conclution

This paper presents a Wirelessly Sensor Networked lighting system for Energy saving and alighting control algorithm based on it. The factor of light is the index of the algorithm. Thelower the sum of the factors of lights are, the more the amount of power that we save.


Fig. 14: Users in No.7 and NO.10 grids at same time

Fig. 15: Users in No.7 and NO.10 grids at same time


Fig. 16: The pulse duration ratio of E

The algorithm proposed concepts of dimming zone, coverage and so on:1. in the dimming process, it takes user’s location as the center, according to the user’s activities

and then ring out a dimming zone. Only the lamps in the zone need lighting decision. The processis unassisted;2. in the above-mentioned point, when multiple users simultaneously in the neighboring grides,

it will make some grides covered with more dimming zone. So we put forward the concept ofcoverage, which is the extent of a zone covering a gride.In the paper, also designes a LED-dimming modul of PWM modulation signal, use 1W LED

as luminaire.

5.2 Prospect

The system is verified correctness of the algorithm in small scale through experiment. Because ofthe wirelessly communicate, the hardware installation can not be undermine the existing lightingsystem, which will reduce the system’s installation costs. Of course, the limitations of the systemstill exist. As follows:1. in the actual environment, algorithm designing did not consider the various effects, such

as the walls, floors, ceilings will absorb parts of light and the obstacles in the environment mayobstruct the light to penetrate. All these will affect our system implementation.2. because each lamp has different distribution curve of light with and deposit these datas

are cumbersome, it is difficult to read light intensity from the distribution curve of light. In thefutrue, we can considered another way to deal withit.3. there is no back-office software in the system, so it is hard for user to set parameters


arbitrarily.4. the system can predigest the wireless sensor node, make it only have the function of wireless

communication.

References

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[6] Wen Yao-Jung, Granderson, J., Agogino, A. M. Towards Embedded Wireless-Networked IntelligentDaylighting 0Systems for Commercial Buildings [J]. Sensor Networks, Ubiquitous, and TrustworthyComputing 2006 (1): 326 – 331.

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Design of Lighting System for Energy Saving Based on Wsn

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