Communications and Network, 2013, 5, 55-60
doi:10.4236/cn.2013.51B013 Published Online February 2013 (http://www.scirp.org/journal/cn)
Design of Energy Saving Lighting System in University
Classroom Based on Wireless Sensor Network
Yu Liang, Ruihua Zhang*, Wei Wang, Caiqing Xiao
School of Computer Science and Technology, Shandong University, Jinan, china
Received 2012
ABSTRACT
In order to reach the objective of intellig ence and energy saving for university classroom lighting, energy saving light-
ing control system in university classroom based on wireless sensor network is designed, including design of sensor
node and sink, as well as corresponding development of control program and upper-computer software. The system sets
single-chip Ameg16 as control center, realizes communication between nodes via nRF24L01 wireless transceiver mod-
ule, and realizes communication between sink and upper computer via w5100 wireless internet module. It perceives
illumination intensity via photoconductor, detects the human body position via infrared pyroelectric sensor, and places
the sensor node on the lamp, so the light can be controlled according to position of human body and cu rre n t illumination
intensity, which can realize energy saving to a large extent on condition that lighting requirement is satisfied. The sys-
tem has low cost, and there is no need to change the original lighting circuit. The light can be turned off by hand, and
when multi-media are used for the class, light can keep off even it is dim. In addition, this system has the function of
automatic fault report, which is convenient for property maintenance.
Keywords: Wireless Sensor Network; Infrared Pyroelectric Sensor; Energy Saving; Lighting System in University
Classroom
1. Introduction
It is a common phenomenon that electricity is wasted in
traditional lighting system of university classroom. Ac-
cording to regulations of national standard, power den-
sity of classroom lightin g is about 10 W/m2. Suppose the
average area of the classroom is 100 m2, then the lighting
load is about 1 kW. If the normal service time is 15 hours
every day, then power consumption of every classroom
every day is 1 kW×15 h＝15 kWh. There are 270 days
when students are at school, so the annual power con-
sumption is about 4050kWh. If the classroom is counted
as 100 m2, then the school has 200 classrooms, so the
power consumption for lighting is about 810,000.00 kWh.
If energy saving rate is calculated as 30%, then
243,000.00 kWh can be saved every year, that is to say,
150,000.00～200,000.00 Yuan of electricity fee will be
saved, and the above estimate does not include line loss
and damaged part of lamps for long service [1]. In terms
of Shandong University, according to statistics, electric-
ity fee in 2005 is 10,470,000.00 Yuan, and it has been
increasing annually [2]. In which power consumption of
lighting accounts for 40% of total electric quantity [3],
and waste caused by delayed turning off or unnecessary
turning on accounts for 70% of power consumption of
lighting. Directed at such wasting phenomena, many
lighting systems have appeared in the market, in which
switch of the light can be controlled automatically ac-
cording to the lighting requirement, so as to avoid the
above energy waste, save expenditure and at the same
time save labor power. Some systems will identify the
indoor light intensity and number of people to control
number of turn-on lamps [4, 5]; some others control the
light according to the region [3,6]. All of these cannot
reach the optimum effect of energy saving, and they re-
quire the original lighting system to change greatly.
In order to make up for the shortcomings of present
technology, system designed by this paper automatically
controls switch of the single lamp according to human
body position and current illumination intensity, which
saves energy to a large extent on condition that lighting
requirements are satisfied.
2. Working Principles of the System
On condition that the original lighting system of the
classroom is not changed, install the sensor node on
every lamp, and adjust the perception range of the sensor
into the largest lamp distance of 2 (often distances
between lamps are not equal, so the largest distance will
*Corresponding author.

Y. LIANG ET AL.
56
be selected) according to the actual requirements, thus
sensor nodes will be placed in the classroom for redun-
dancy. Every sensor node perceives human signal and
current illumination inten sity, which directly controls the
light. There is communication between sensor node and
sink, so sensor and lamp state in the classroom can be
reflected to sink. There is one sink in every classroom,
which is connected into internet (LAN) via screen wire.
All information gathers into the computer that acts as a
server via internet for information integration, gathering
and disposal as well as providing necessary Web service.
The director can lodge in Web server via any networking
PC or even mobile phone to inquire or control state of all
nodes in the classroom. The system structure is shown in
Figure 1.
The sensor is arranged acco rding to the lamp position.
Height of the classr oom is 3.4 m, perception ang le of in-
frared pyroelectric sensor is 120 degree, and adjust resis-
tance and lens to make radius of sensor coverage range
be the largest lamp distan ce of 2. In general situation,
one person can be detected by 1 or 2 sensors, such as the
white and grey part in Figure 2, and in special situations,
one person can be detected by 3 or 4 sensors, such as the
bend and dark part in Figure 2. Therefore, 4 lamps can
be turned on at most.
Figure 1. System structure diagram.
Figure 2. Human signal detection diagram.
Control of turning on and off the light by automatic
detection in the classroom: under the condition of insuf-
ficient light, when people walk in or past the classroom,
the light will not b e turned on. Only when p eople stay or
sit in a position, will 1 lamp above be turned on, and in
special situations, will 4 lamps be turned on at most.
When people are seated, as long as there is tiny move-
ment within 5 minu tes, the ligh t will keep on . When peo-
ple leave, 5 minutes later, the lamp at corresponding po-
sition will be turned off. Under the co nd ition of sufficien t
light, the light will not be turn ed on. In addition, the sys-
tem can automatically detect damaged lamp node and
sensor node, and report to upper computer, asking for
maintenance.
Control of turning off the light by hand in the class-
room: when multi-media are used for classes in the
classroom, the light may be insufficient, and when there
are people in the classroom, the light will be turned on
automatically, but actually, there is no need to turn on the
light. Therefore, switch of the original lighting system
can be used to turn of f the light by ha nd .
Overall working of the system: firstly, turn on the
original circuit switch to make the circuit unimpeded for
automatic control by the system. When people enter into
the perception range of the sensor, the sensor will detect
current light value. If the light is insufficient, lamp con-
trolled by the sensor node will be turned on, (after order
of turning on the light is given, the light value will be
detected again, and if the light is still insufficient, order
of turning on the light will be given again. If the light is
still insufficient after 3 times, then the node is judged to
be damaged). When people leave the perception range,
there is a delay time for the light to be turned off. In
terms of information that state of the sensor node storage
lamp changes, when sink checks this sensor node, the
current state will be sent to sink (if sink does not receive
the reply, the sensor node will be judged to be damaged).
Sink will make judgment after summarization, then pass
the updated information to the upper computer. Accord-
ingly, the upper computer can also actively issue inquiry
or control orders which will be passed to sensor node via
sink, to get corresponding information or control turning
on and off the light. Under special conditions, such as
multi-media are used, the light can be turned off by hand
via original switch of the circuit.
3. System Hardware Design
This system realizes two kinds of nodes: sensor node and
sink.
3.1. Sensor Node
The sensor node consists of the following components:
infrared pyroelectric sensor, photoresistance, wireless

Y. LIANG ET AL.
57
transceivers, center processing chip, 5v power converter
and relay. The hardware design circuit is shown in Fig-
ure 3.
with the 3.3v power. This module employs 2.4 GHz with
the distance about more than 10 meters. It can be pro-
grammed to set the location, only when receiving the
location of this single-chip, can the data be output (inter-
rupt indication is provided).
U1 is the central processing component unit. Both the
sensor node and sink employs ATMEGA16L-8PU AVR
single-chip. Eight-binary AVR microprocessors using the
same single-chip can avoid the complexities in the coor-
dination to develop various chips, reduce the system cost
and the difficulties in maintenance. And the pro- gram-
mers are familiar with Amega16, which is easy for de-
velopment.
P4 is the infrared pyroelectric sensor module
BISS0001 with three pins, among which the 1st pin con-
nects with the high level, the 2nd pin connects with the
single-chip PA0 as the output of the collected data, and
the 3rd pin connects with the low level. Its operation
principle is that when anyone enters its detection zone,
high level will be outputted, while anyone leaves its de-
tection zone, low level will be outpu tted automatically.
P2 is the wireless module nRF24L01, which employs
SPI serial communication to communicate with mega16.
This module has 8 pins, among which the 2nd pin con-
nects with the single-chip MISO as the SPI output pin,
the 3rd pin connects with single-chip MOSI as the SPI
input pin, the 4th pin connects with the single-chip SCK
as the SPI clock signal pin, the 5th pin connects CSN as
the SPI enable pin, the sixth pin connects with the single-
chip SCK as the mode selection pin, the 7th pin connects
3.2. Sink
Sink consists of the following components: wireless tran-
sceivers, central processing chip mega16 and Ethernet
communication module. The hardware design circuit is
shown in Figure 4.
Figure 3. Hardware co nne ction chart for sensor node.
Figure 4. Hardware connection chart for sink.

Y. LIANG ET AL.
58
P6 is SW5100 module with 10 pins, among which the
1st pin connects with the single-chip MISO as the
SW5100 module SPI output pin, the 2nd pin connects
with the single-chip MOSI as the SW5100 module input
pin, the 3rd pin connects with the single-chip SCS as the
low-efficient chip selecting signal, the 4th pin connects
with the single-chip SCLK as the SPI clock signal pin.
W5100 Ethernet communication module realizes the
connection with the internet and sinks through the cable.
Since there are network ports in the classrooms, this
module can be selected to reduce the changes in the
original lighting system.
4. System Software Design
4.1. Sensor Node
The followings are the functions of the sensor node.
1) The values of the infrared pyroelectric sensor and
photo resistance are collected periodically to maintain the
delay_3s_open_lam and delay_max_5min_close_lamp.
The condition of the switch can be judged through the
two values to turn on or off the light.
2) When the commands for turning on or off the lights
are given, the illumination values would be collected
again to judge if the nodes are damaged.
3) According to the commands from the sink, the
lights will be controlled or messages will be sent to sink.
The control process for the sensor node is shown in
Figure 5.
Figure 5. Control process chart for the sensor node.
Illumination intensity and the positions of the person-
nel are regarded as the basis for the system control. The
sensor nodes in the classroom are coded uniformly. Each
sensor node will detect the values of the infrared py-
roelectric sensor and photo resistance to maintain the two
delay values, namely delay_3s_open_lamp and delay_
max_5min_close_lamp. The sensor node will determine
the status of the switch from the two values to control the
switch. If the sensor node receives the commands from
sink, it will judge the command type, and the control
command will control the switch according to the com-
mand, while the query command will return to the cur-
rent status.
Among which, three problems should be solved when
employing the infrared pyroelectric sensor to detect the
position of human.
1) The perception scop e of the sensor is too large, and
the radius of the sensor which has not been treated is 4 m
(following the above designed height for the classroom).
It cannot be used to confirm the specific location , but the
perception radius can be decreased to the largest lamp
distance of 2 through adjusting the resistance value
of the module and optical lens.
2) According to the perception principle of the infrared
pyroelectric sensor, the testing basis for the human signal
is the relative movement, namely, if the human keeps
motionless, even in the perception scope, the sensor
cannot perceive, which is quite inapplicable in the class-
room. The students in the classroom cannot stay still at
any time. During the control procedure design process,
delay_max_5min_close_lamp is introduced to avoid the
misjudgment because of the stillness. If no signals for
human are detected, it will turn down five minutes later.
If the delay exhausts but there is still ex istence of human,
the delay will be updated. Then when there is a tiny
movement in the five minutes, it can be detected.
3) If nothing has been done and th ere is on e passing by,
a light will turn off after being turned on, which is un-
necessary. The twinkle of lights will be harmful to the
human body. Delay_3s_open_lamp has been introduced,
namely in 3 s continuous test, there are signals for human,
it can be confirmed that someone has stopped at some-
where instead of passing by.
4.2. Sink
The followings are the major functions of th e sink:
1) Take turns to check the sensor node, achieve the
switch status of the sensor node, photo resistance vale,
and infrared pyroelectric sensor value, update the status
information of the sensor for the maintenance on sink.
After a cycle, if there are changes in the status of the
light, it will send messages to the upper-computer. If the
query demand from the upper-computer is received, in-
formation about the status of the light and current sensor

Y. LIANG ET AL. 59
node will be sent to the upper-computer.
2) If the control command has been received from the
upper-computer, it will be sent to th e corresponding sen-
sor.
Sink will take turns to check each sensor node regu-
larly, which will avoid the collision with th e sensor node
for active uploading. There are th ree major objectives for
taking turns to check:
1) Send message to the sensor node to check if there
are any changes in the status of the lights.
2) To see if the sensor node is broken (if there is no
respond, the sensor node has been broken).
3) If commands for controlling the switch are received
from the upper-computer, then turning to check this node,
control command should be sent to the sensor node. Af-
ter receiving the command, the sensor node will send
messages for turning on or off the switch to the sink.
The sink would maintain the information for the sen-
sor node and status of the light through taking turns to
check, and changes will be updated after the check. If
there is any change in the status of the switch of the light
(including whether it’s broken), then messages will be
sent to the upper-computer, which would calculate the
lighting time according to the information. Meanwhile
the upper-machine can also check the state values of each
sensor node through these messages. The control process
chart is shown in Figure 6.
Function design for upper-computer PC serving as the
upper-c o mputer, realize the following ma j or functions:
1) Show the serial number of the sensor nodes and
sinks in the classroom.
2) Check the current status of the lights and sensor
nodes in the classroom.
3) Control the switch of the lights in the classroom.
4) Keep a record for the historical information of the
switch and calculate the electricity consumption.
Realization interface is shown in Figure 7.
Figure 6. Control process chart for the sink.
5. System Testing
System testing follows the following procedure:
1) Firstly design and realize the sensor node and sink,
and achieve success within the stated communication
scope.
2) Allocate the sensor node on each light in an expe-
rimental classroom, transform the circuit to make the
sensor node control the switch, the transmission of the
test data and test for success of the incident.
3) Arrange the sinks in a place in which all the sensor
nodes can be covered within the communication distance
of the wireless module, the sensor nodes and sinks can
work.
4) Test the communications between the sink and the
upper-computer.
5) Test the control over the switch of th e light, and test
if the upper-computer can control the switch of the light
by sending commands.
6) Overall test of the system: a person walks a distance
and sits at somewhere. In the test result, the roadside
lights passed do not turn on, while the one above the
place where the person sits turns on. When he leaves, the
light will turn down automatically. The result of the up-
per-computers is shown in Figure 8.
Suppose that the average acreage of the classroom is
100m2 and there are 15 lights. Accord ing to this calcula-
tion method, in most cases, when one enters the class-
room, he would turn on one or two lights, maybe in spe-
cial conditions he would turn on 4 lights. If several stu-
dents sit closely in the classroom, the number of the
lights would not increase. Under such condition, the
Figure 7. Display Interface for the power consumption in
each classroom.
Figure 8. Real time display of the information of the class-
room.

Y. LIANG ET AL.
60
illumination scope of the two lights is about 15 m2. Ac-
cording to the national standards, the illumination power
density of the classroom is about 10 W/ m2, then the il-
lumination load power about (100 m2-15 m2)×10 W/ m2
= 850W can be saved. If the normal service time is 15
hours every day (it is the worst situation, generally we
can turn off the lights in the daytime), then about 0.85
kW×15 h＝12.75 kWh power consumption can be saved
for each classroom in one day. The students will be at
school for 270 days in each year, and then the annual
saved power is about 3442 kWh. If the school has 200
classrooms, so the predicated annual saved power is
about 690000 kWh.
6. Conclusions
Compared with the tradition al energy saving control sys-
tem for the lights in the classroom, allocating sensor
nodes on the corresponding lights can help get the gen-
eral position of the human body, and then turn on the
corre- sponding lights to save the energy substantially on
the premise of satisfying illumination demand. Besides,
this design based on wireless sensor network can not
only decrease the changes in the original lighting system,
but also get prepared for the expansion of the intelligent
classroom. By adopting B-S structure, the upper-com-
puter can check the current status of the classroom online
freely. It can also know if there are broken lights or sen-
sor node in the classroom at any ti me, which would br ing
convenienc e for the maintenance work. In today’s avoca-
tion of energy saving, such low-cost and convenient en-
ergy saving system would certainly be widely used.
7. Acknowledgements
This work was partially sponsored by the Natural Sci-
ence Foundation of China (NSFC) under grant No.
60903031 and 61070022, the Teaching Reform of Shan-
dong University under grant No. 11480071188178.
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