The document describes a design for an automatic room light detection and control system called the HLCM (Home Light Control Module). Key points: - The HLCM uses PIR sensors to detect human presence, light sensors to measure light intensity, a microprocessor to control lights via solid state relays, and an RF module to enable communication between HLCM units. - The HLCM can turn lights on or off to maintain sufficient light levels based on measurements from the light sensors. It can also activate lights in adjacent areas via RF communication to pre-emptively provide lighting where a person is moving to. - Experimental results showed the HLCM can accurately measure and control light levels, with communication between units. It provides automatic

1. Y.-W. Bai and Y.-T. Ku: Automatic Room Light Intensity Detection and Control Using a Microprocessor and Light Sensors
Contributed Paper
Manuscript received July 7, 2008 0098 3063/08/$20.00 © 2008 IEEE
1173
Automatic Room Light Intensity Detection and Control
Using a Microprocessor and Light Sensors
Ying-Wen Bai and Yi-Te Ku
Abstract — In this paper we propose a design using both a
microprocessor and light sensors for automatic room light
detection and control. Our design, the HLCM (Home Light
Control Module) which will be installed in every light fixture
of a family, is made up of four blocks: the pyroelectric
infrared (PIR) sensor circuit, the light sensor circuit, the
microprocessor and the RF module. By using the PIR sensor
circuit, the HLCM detects if a human body enters the
detection area or not. If there is no human body present, all
controlled lights are turned off. If there is, the HLCM detects
the light intensity under the environment and maintains
sufficient light by controlling the number of lights. We have
also integrated an RF module to transmit and receive the data
from each HLCM so we can control different lights in
different regions. The result of using the HLCM shows that the
total power consumption can be reduced1
.
Index Terms — Light Control, Microcontroller, Pyroelectric
Detectors, Illumination Measurement
I. INTRODUCTION
In recent years the energy crisis has become one problem
which the whole world must confront. Home power
consumption makes up the largest part of energy consumption
in the world. In particular, the power consumption of lamps in
a typical home is a factor which can’t be ignored. The typical
user needs different light intensities in different places.
Sometimes the light intensity from outside is sufficient, and
thus we don’t need to turn on any light. But sometimes the
user leaves but forgets to turn off the light. These factors
cause energy waste. Therefore some power management of
light control in a home is necessary in order to save energy.
Lights are usually controlled by on/off switches. Of course,
the user can switch a light on or off remotely by connecting a
specific device to a PC, but there has to be at least a PC,
consuming a rather large amount of power 24 hours a day, for
the control mechanism [1-4]. Moreover, this inconvenient
practice comes at a high cost for the user. In some designs one
must install specific hardware and software to control the
lights, resulting in unacceptable costs. Furthermore this type
of system cannot detect either the temperature of the human
body or the room light intensity [5-8].
In this paper we propose a design for automatic room light
detection and control. As shown in Fig. 1, we install a low-
1
Ying-Wen Bai is with the Department of Electronic Engineering, Fu-Jen
Catholic University, Taipei, Taiwan, 242, R.O.C. (e-mail: bai@ee.fju.edu.tw)
Yi-Te Ku is a graduate student of Fu-Jen Catholic University, Taipei,
Taiwan, 242, R.O.C. (e-mail: 495506100@mail.fju.edu.tw)
power HLCM in every lamp in a typical home. The design
detects whether someone is passing through the detection area
not only by means of the PIR sensor in the HLCM but also by
detecting the change of light intensity in a room by means of
the light sensor in the HLCM. We also use the RF module to
communicate among the HLCMs to pre-control the lights. For
example, when the room light intensity is insufficient, all
lights controlled by HLCM A are turned on. HLCM A will
then send a signal to the nearby HLCM B to turn on a light
controlled by HLCM B to increase the light intensity.
Moreover, if someone goes from the kitchen to the living
room, the HLCM in the kitchen notifies the HLCM in the
living room to turn on the light in advance. By using our
design one can achieve high efficiency in home power
management.
This paper is organized as follows. Section 2 introduces the
HLCM. Section 3 presents the light control in our design.
Section 4 summarizes the implementation results and Section
5 draws our conclusion.
HLCM HLCM
HLCM
HLCM HLCM
HLCM HLCM
RF
RF
RF
RF
RF
RF
RF
Fig. 1. Room light intensity detection and control architecture.
II. DESIGN OF THE HLCM
The HLCM shown in Fig. 2 is made up of the PIR sensor
circuit, the light sensor circuit, the RF module and the low-
power MCU. We also provide a DC power supply from AC
power to every component.
We use the PIR sensor circuit to detect whether someone is
passing through the detection area or not. If a human body
enters the detection area, the PIR sensor receives the
variations of the temperature made by the infrared energy
emitted to the surroundings, and if necessary produces the
variations of electric changes by means of a pyroelectric effect.
Because the electric charges are very few and not easily
sensed by the sensor, we adopt the high-impedance FET to
pick up the signal. Since the output amplitude of the sensors
we measure, about the level of mV, is not large enough for an
MCU, we have to amplify the output signal from the sensor
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2. IEEE Transactions on Consumer Electronics, Vol. 54, No. 3, AUGUST 2008
1174
with a sufficient quantity of two-stage high-gain amplifiers.
Nevertheless, if the gain is very high, most tiny noises are
amplified simultaneously and interfere seriously with the
output signal. Therefore, in our design we have adjusted the
value of both the resistance and the capacitance so as not only
to amplify the sensed signal and but also to restrain any noise
resulting from the temperature variations.
R VDD
MCLR
AVDD
AVSS
B0
VCC
VSS
A0
A1
MCU
R
VCC
R
R
R
R
R
C
C
R
R
Light sensor circuit
R
Light
sensor
7805
C C
D
D
D D
R R R
T
L
L
Power supply circuit
R
C
VCC
R
R
C
PIR
sensor
R
R
R
R
C
C
C
C
PIR sensor circuit
AC power
OSC1
OSC2
C
C
1M
B1
VCC
VCC
TX
RX
AC power
SSR
RF module
…
…
…
…
TX
RX
VDD
VSS
R
SSR
C
Fig. 2. The circuit diagram of the HLCM.
The RF module is specifically designed to connect to the
MCU, thus allowing communication to be made among the
HLCMs. The modulation of the RF communication is FSK,
and the FM modulator works at 2.4 GHz frequency and 2
MKbps speed. The advantages of RF communication are the
absence of extra connection wires and its low cost.
We have used an SSR to switch each light. SSRs have been
utilized to replace mechanical relays because of their many
advantages, like miniaturized configuration, little or no
contact bounce, low energy consumption, decreased electrical
noise, compatibility with digital circuitry and high-speed
switching performance. These SSR also provide isolation
between a control circuit and a switched circuit.
The MCU in the HLCM has three functions, as shown in
Fig. 3: to support sufficient light intensity by ascertaining in
which room the user is located, detecting the human body, and
switching lights on/off by controlling the solid state relays
(SSR) on/off.
Fig. 3. The control flowchart of the microprocessor.
III. DESIGN OF THE LIGHT CONTROL BY HLCMS
A. Light controlled by an HLCM
As shown in Fig. 4, we install an HLCM at each light. The
HLCM detects if a human body is present or not and it detects
the light intensity; it switches each light on/off by controlling
the SSR on/off to support sufficient light intensity.
Fig. 4. Light controlled by an HLCM.
In our design setting the HLCM measures the average light
intensity supported by a light, which is 170 Lux, and the
power consumption of a light, which is 80 Watts. When a user
turns on all lights, the power consumption increases to 400
Watts. Because there are different levels of sufficient light
intensity in different places, the number of lights switched on
is different. In Table I we give examples from three different
places.
TABLE I
POWER SAVING IN DIFFERENT PLACES
Room Living room Bathroom Study room
Sufficient light
intensity
150 Lux 200 Lux 500 Lux
Number of lights
switched on by
HLCM
1 2 3
Power consumption 80 Watts 160 Watts 240 Watts
Power saving
(Watt, %)
320 Watts,
80%
240 Watts,
60%
160 Watts,
40%
B. The Communication among HLCMs
As shown in Fig. 5, we use the RF module to transmit and
receive the data from each HLCM in order to pre-control the
lights and support sufficient light intensity. If the light
intensity is still insufficient for the user when all the lights
controlled by HLCM A are turned on, HLCM A will ask the
nearest HLCM B to turn on a light controlled by HLCM B to
increase the light intensity. Pre-control means that if someone
goes from the kitchen to the living room, the HLCM in the
kitchen notifies the HLCM in the living room to turn on the
light in advance. The communication format has four parts:
the address of the HLCM (24 bits), the address of the light
devices (5 bits), the status of light (3 bits) and the CRC
(Cyclic Redundancy Check, 8 bits).
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3. Y.-W. Bai and Y.-T. Ku: Automatic Room Light Intensity Detection and Control Using a Microprocessor and Light Sensors 1175
Preamble Address Data CRC
D D D D D S S S
00001 Light_1
00010 Light_2
00011 Light_3
001 Switch on
010 Switch off
D Address of lights
S Status of lights
Fig. 5. The message format for light control.
IV. RESULTS OF THE EXPERIMENT
Fig. 6 shows the implementation of the HLCM. The
hardware prototype circuit of the HLCM is now
implemented on an 8 cm × 6 cm printed circuit board
(excluding the SSR).
The power consumed by the HLCM can be measured
and calculated as shown in Table II.
We compare the change of the value of light intensity
under the same environment between that measured by
our design and that of the traditional design measured by
a digital light meter. We place a digital light meter 200
cm below a light. Because the HLCM is adjacent to the
light, and the light intensity measured by an HLCM is
higher than that measured by a digital meter, we have to
adjust the value measured by the HLCM to make it
similar to that measured by the digital light meter, as
shown in Fig. 7.
RF module
Light
sensor
PIR
sensor
Fig. 6. Picture of an HLCM.
TABLE II
AVERAGE POWER CONSUMPTION OF THE HLCM MODULE
Item
Average
Current (mA)
Operation
Voltage
(V)
Average Power
Consumption
(W)
RF 33 3 0.099
MCU 36 5 0.18
Relay 68 5 0.34
Body
Detection
35 5 0.175
Light
Detection
38 5 0.19
Total 210 5 or 3 0.984
0
500
1000
1500
2000
2500
3000
0 120 240 360 480 600 720
Time(Minutes)
Illumination
(Lux)
Valuemeasured by our design Valuemeasured by digital light meter
Fig. 7. Comparison of the light intensity measured by our design and that
measured by a digital light meter.
As shown in Fig. 8, we measure the variations of light
intensity of three modes for a long time under the same
environment. The three modes are the change of light intensity
in nature, the change of light intensity when we switch the
light on/off by ourselves and the change of light intensity
when we install the HLCM at the light. In our experiment we
observe the light intensity when in user time; we do not
observe the light intensity when in non-user time. Under
natural conditions the room light intensity changes along with
the outside environment. When we do the switching by
ourselves there is one condition: When we switch all lights on
because the environment is too dark or when we do not switch
the lights off when just leaving for a short time, we maintain
enough light intensity. When we switch the lights on/off by
using the HLCM, the light intensity is the same as under
natural conditions and it is maintained at over 500 Lux if there
is a user. When the user leaves the room or the light intensity
is more than 1000 Lux, the light is turned off.
0
500
1000
1500
2000
2500
0 720 1440 2160 2880 3600 4320
Time (Minutes)
Illumination
(Lux)
The change of light intensity in nature
The change of light intensity when we switch the lights on/off by ourselves
The change of light intensity when we install the HLCM at the light
Sunny Cloudy Partly cloudy
User
time
Non-user
time
User
time
User
time
Non-user
time
Non-user
time
Fig. 8 The change of room light intensity under three modes.
In Fig. 9 we have compared the power consumption
between switching the lights on/off by ourselves and using the
HLCM. Our measurement confirms that energy is saved by
using the HLCM.
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4. IEEE Transactions on Consumer Electronics, Vol. 54, No. 3, AUGUST 2008
1176
0
50
100
150
200
250
300
0 720 1440 2160 2880 3600 4320
Time (Minutes)
Power
consumption
(Watts)
Switching the lights on/off by ourselves
Switching the lights on/off by using the HLCM
Sunny Cloudy Partly cloudy
Fig. 9. Comparison of the power consumption of our design with that of
other designs.
V. CONCLUSION
In this paper we have proposed a design for automatic room
light detection and control. We install an HLCM at every light
of a family for home power management. The HLCM detects
if a human body is present or not by using the PIR sensor
circuit. If there is no human body present, all lights are turned
off. If there is, the HLCM then detects the light intensity
under the environment by using the light sensor circuit and the
system maintains sufficient room light by switching lights
on/off. To realize light intensity support and light pre-control,
the RF technology for light power management has been
integrated. Consequently, the potential of the features of low
cost, small size, low power consumption and power saving
has been shown.
Table III, a comparison of designs, shows that our design
consumes less power, and at a low cost. As a result, our
design, which has more integrated functions, is better than
others.
TABLE III
COMPARISON OF OUR DESIGN WITH OTHERS
Light Control Design Design 1 Design 2 Our Design
Home Server Needed Needed Not Needed
Power Consumption 120 Watts 25 Watts ≤ 0.984 Watts
Body Temperature
Detection
No No Yes
Light Control No No Yes
Cost High High Low
Setup Complicated Easy Easy
Pre-control No No Yes
Light Intensity Setting
Support
No No Yes
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Ying-Wen Bai is a professor in the Department of
Electronic Engineering at Fu-Jen Catholic
University. His research focuses on mobile
computing and microcomputer system design. He
obtained his M.S. and Ph.D. degrees in electrical
engineering from Columbia University, New York,
in 1991 and 1993, respectively. Between 1993 and
1995, he worked at the Institute for Information
Industry, Taiwan.
Yi-Te Ku is currently working toward the M.S.
degree in Electronic Engineering at Fu-Jen Catholic
University, Taiwan. He received his B.S. degree in
electronic engineering from Fu-Jen Catholic
University in 2006. His major research is focus on
consumer electronics products and microcomputer
system integration design.
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