WO2013165126A1

WO2013165126A1 - Energy saving lighting system

Info

Publication number: WO2013165126A1
Application number: PCT/KR2013/003606
Authority: WO
Inventors: Min Jun Jang
Original assignee: Min Jun Jang
Priority date: 2012-04-30
Filing date: 2013-04-26
Publication date: 2013-11-07
Also published as: KR101266830B1; TW201401933A

Abstract

A lighting system is capable of synchronizing the flickering timings of light sources, improving the apparent brightness felt by a user and saving energy. The lighting system a plurality of light sources, a synchronizing signal generator configured to generate a synchronizing signal for synchronizing flickering timings of the light sources, and a plurality of controllers installed in a corresponding relationship with the light sources. The controllers are configured to synchronize the flickering timings of the light sources by receiving the synchronizing signal and PWM (Pulse Width Modulation)-controlling the light sources in response to the synchronizing signal.

Description

ENERGY SAVING LIGHTING SYSTEM

The present invention relates to an lighting system and, more particularly, to an lighting system that can synchronize the on-off timings of plurality of light sources, thereby enhancing the apparent brightness felt by a user and consequently saving energy.

A luminaire denotes a device for converting electric energy to light energy. Typically, the amount of light energy generated is increased in proportion to the amount of electric energy inputted. The ratio of the electric energy converted to the light energy is referred to as light conversion efficiency.

An improvement in the light conversion efficiency leads to the saving of electric energy. Many different efforts such as the light conversion efficiency improvement of an element, the power-factor improvement of a power supply device and the light distribution optimization have been made in order to realize high-efficiency illuminator.

In recent years, an attempt to save energy in a pulse-wave-driven lighting device has been made from the viewpoint of psychophysics which is a scientific study on the relationship between a recognition phenomenon and a physical property of stimuli.

A light emitting diode (LED) is controlled by a Direct Current (DC) control method using a DC power supply or a pulse width modulation (PWM) control method using a pulse power supply.

The pulse width modulation control method is a method in which electric power is controlled by adjusting the frequency and duty cycle of pulses. A light source flickering at a frequency higher than a flicker fusion frequency is felt by the human eyes as if it were continuously turned on instead of intermittently flickering. Accordingly, if a light emitting diode is driven by a pulse voltage having a frequency higher than a flicker fusion frequency, the human eyes feel that the light emitting diode is continuously turned on. Most of the human eyes feel a light source flicking at a frequency of 75 Hz or more as if it were continuously turned on.

Results of study on how the human eyes will recognize the brightness of an intermittently flickering light source have been announced since 1900′.

Pursuant to the Talbot-Plateau law, it is said that a human observing an intermittently flickering light source feels as if the light source were continuously turned on at average brightness.

According to the Broca-Sulzer law, it is said that, when exposed to intense light such as camera flash light or the like, the human eyes feel the light several times brighter than the actual brightness.

A recent study¹⁾ conducted at the Ehime University, Japan, reveals that the Broca-Sulzer effect has a stronger influence than the Talbot-Plateau effect in case of using a pulse voltage and further that the human eyes recognize a light source brighter than average brightness.

A study²⁾ conducted at the Tianjin University, China, reveals that, as shown in Fig.1, an LED driven by a PWM control method is felt brighter than an LED driven by a Direct Current (DC) control method, if the average brightness remains the same. It can be seen in Fig. 1 that the difference in apparent brightness between the PWM control method and the Direct Current (DC) control method becomes larger as the duty cycle of a pulse becomes shorter. The term "apparent brightness" means a psychological amount of light and shade corresponding to the brightness as a physical quantity of light. In other words, the apparent brightness does not mean the actual brightness but does mean the brightness felt by a human.

Referring to Fig. 1, it can be noted that, if the duty cycle is 50% when the frequencyis 100 Hz, the LED driven by the PWM control method is felt about 40% brighter than the LED controlled by the Direct Current (DC) control method. If the duty cycle is 80%, the LED driven by the PWM control method is felt about 25% brighter than the LED controlled by the Direct Current (DC) control method. If the duty cycle is 100%, the LED driven by the PWM control method does not differ in brightness from the LED controlled by the Direct Current (DC) control method.

Such a result can also be confirmed in the study conducted at the Ehime University, Japan. The result of study of the Ehime University reveals that, when driven at a duty cycle of 5% by a pulse of 60 Hz, the LED driven by the PWM control method is felt 120% brighter than the LED controlled by the Direct Current (DC) control method.

It can be expected from the results shown in Fig. 1 that, if the average intensity remains the same, an LED driven by a pulse voltage higher in intensity and shorter in duty cycle will be recognized brighter than an LED driven by a pulse voltage lower in intensity and longer in duty cycle.

[Prior Art References]

[Non-Patent Documents]

1): Masafumi JINNO, Keiji MORITA, Yudai TOMITA, Yukinobu TODA, Hideki MOTOMURA(2008), "Effective illuminance improvement of light source by using pwm", J. Light & Vis. Env. Vol. 32, No. 2, 2008.

2): Zhang Yinxin, Zhang Zhen, Huang Zhanhua, Cai Huaiyu, Xia Lin, Zhao Jie(2008), "Apparent Brightness of LEDs under Different dimming Methods" Proc. of SPIE Vol. 6841 684109.

In case where several LED luminaires irradiate light on the same region, even though the LED luminaires are driven by the PWM control method, no meaningful difference exists between the PWM control method and the Direct Current (DC) control method unless the flickering timings of the LED luminaires are synchronized.

Figs. 2A, 2B and 2C are diagrams for explaining the difference in apparent brightness depending on the phase difference of two LED luminaires driven by the PWM control method. Fig. 2A illustrates a case where the flickering timings are synchronized. Fig. 2B illustrates a case where a phase difference of 180 degrees exists between the flickering timings. Fig. 2C illustrates a case where a phase difference of 90 degrees exists between the flickering timings. The intensity of a pulse voltage used in the PWM control is 100 and the duty cycle is 50%.

If the flickering timings of two LED luminaires are synchronized as illustrated in Fig. 2A, the LED luminaires work as if they were driven by a pulse voltage having an intensity of 200 and a duty cycle of 50%. If a phase difference of 180 degrees exists between the flickering timings as shown in Fig.2B, the LED luminaires work as if they were driven by Direct Current (DC) having an intensity of 100 and a duty cycle of 100%. If a phase difference of 90 degrees exists between the flickering timings as shown in Fig. 2C, the LED luminaires work as if they were driven by a pulse voltage having an average intensity of 400/3 and a duty cycle of 75%.

As shown in Fig. 1, the apparent brightness available when an LED is driven by a pulse voltage having a duty cycle of 50% is higher than the apparent brightness available when an LED is driven by a pulse voltage having a duty cycle of 75% or Direct Current (DC). Referring to Fig. 1, the apparent brightness available when an LED is driven by a pulse voltage having a duty cycle of 50% is about 40% higher than the apparent brightness available when an LED is driven by Direct Current (DC).

In a conventional Lighting system including a plurality of luminaires driven by a PWM control method, the luminaires are not synchronized. For that reason, no meaningful difference in apparent brightness exists between the luminaires driven by a PWM control method and the luminaires driven by Direct Current (DC). Another problem lies in that the apparent brightness varies depending on the phase difference of pulse voltages for driving individual luminaire.

In view of the problems noted above, it is an object of the present invention to provide a lighting system capable of saving energy by consuming a reduced amount of electric power. Another object of the present invention is to provide a lighting system capable of keeping constant the apparent brightness felt by a user.

In order to achieve the above objects, the present invention provides an energy saving lighting system, including: a plurality of light sources; a synchronizing signal generator configured to generate a synchronizing signal for synchronizing flickering timings of the light sources; and a plurality of controllers installed in a corresponding relationship with the light sources, the controllers configured to synchronize the flickering timings of the light sources by receiving the synchronizing signal and PWM (Pulse Width Modulation)-controlling the light sources in response to the synchronizing signal.

In the energy saving lighting system, the synchronizing signal generator may be installed between each of the light sources and an AC source for supplying an alternating current to the light sources, the synchronizing signal generator configured to generate the synchronizing signal by sensing a phase change of the alternating current. For example, the synchronizing signal generator may be a zero-cross detector configured to generate the synchronizing signal by detecting a moment at which an instantaneous value of a voltage of the alternating current becomes zero.

The light sources are preferably controlled at a pulse width modulation switching frequency of from 100 Hz to 1 kHz and at a duty cycle of from 10% to 85%.

More preferably, the light sources are controlled at a pulse width modulation switching frequency and at a duty cycle of from 10% to 85%, the pulse width modulation switching frequency being a dual frequency including a first switching frequency of from 100 Hz to 1 kHz and a second switching frequency lower than the first switching frequency.

The energy saving lighting system according to the present invention is capable of maintaining the same level of apparent brightness as available in other conventional lighting systems while consuming a relatively small amount of electric power as compared with other conventional lighting systems. Accordingly, the present lighting system has an advantage in that it can save energy. The present lighting system provides another advantage in that it can keep constant the apparent brightness felt by a user.

Fig. 1 is a graph showing a change in the ratio of apparent brightness and average intensity depending on a duty cycle.

Figs. 2A, 2B and 2C are diagrams for explaining the difference in apparent brightness depending on the phase difference of two LED luminaires driven by a PWM control method.

Fig. 3 is a block diagram showing an energy saving lighting system according to one embodiment of the present invention.

Fig. 4 is a block diagram of an energy saving lighting system according to another embodiment of the present invention.

Fig. 5 is a block diagram showing an energy saving lighting system according to a further embodiment of the present invention.

Fig. 6 is a block diagram showing an energy saving lighting system according to a still further embodiment of the present invention.

Fig. 7 is a diagram for explaining a pulse form in case where a pulse width modulation switching frequency is a dual frequency.

Fig. 8 is a diagram for explaining an improvement in apparent brightness in case where a pulse width modulation switching frequency is a dual frequency.

The present invention will now be described in detail with reference to the accompanying drawings.

The embodiments to be described later are presented by way of example in an effort to sufficiently transfer the concept of the present invention to those skilled in the art. Therefore, the present invention is not limited to the following embodiments but may be embodied in many other forms.

Fig. 3 is a block diagram showing an energy saving lighting system according to one embodiment of the present invention. As shown in Fig. 3, the energy saving lighting system according to one embodiment of the present invention includes a plurality of light sources 10, a plurality of synchronizing signal generators 20, each of which generates a synchronizing signal for synchronizing the flickering timings of the light sources 10 and a plurality of controllers 30 for controlling the light sources 10.

The light sources 10 are spaced apart from one another and are configured to irradiate light on the same region. The light sources 10 could be a plurality of luminaire installed in a living room, a pair of headlights of a vehicle, a plurality of luminaire installed in an underground parking lot, etc. It is an object of the present invention to provide an energy saving lighting system capable of synchronizing the flickering timings of the light sources 10 and capable of keeping constant the apparent brightness felt by a user while consuming a relatively small amount of electric power.

Each of the light sources 10 maybe an LED array formed of a single LED element or a plurality of LED elements. The LED elements can be connected to one another in series or in parallel. The LED array may be formed by parallel-connecting a plurality of strings, each of which includes a plurality of serially-connected LED elements. The respective light sources 10are connected to one and the same AC power source 1. Rectifying circuits 40 for converting an alternating current to a direct current are arranged between the AC power source 1 and the light sources 10. Each of the rectifying circuits 40 may include a voltage transformer for transforming the voltage of the alternating current inputted, a bridge diode circuit for rectifying the alternating current into a semi-sinusoidal wave current, a capacitor for smoothening the semi-sinusoidal wave current and a voltage regulator for regulating a voltage.

Each of the synchronizing signal generators 20 is configured to generate a synchronizing signal for synchronizing the flickering timings of the light sources 10 so that the light sources 10 can flicker at the same time. In the present embodiment, the synchronizing signal generators 20 are installed between the AC power source 1 and the respective controllers 30 and are configured to generate synchronizing signals depending on a change in the phase of the alternating current. The synchronizing signal generators 20may be zero-cross detectors.

The zero-cross detectors are configured to generate synchronizing signals by detecting the moment at which the instantaneous values of the voltage of the alternating current become zero. Since all the light sources 10 are operated by the same AC power source 1, the instantaneous values of the voltage of the alternating current become zero at the same moment. Accordingly, the zero-cross detectors installed at the AC power input ends of the respective light sources 10 can be used as the synchronizing signal generators 20.

The zero-cross detectors can be manufactured through the use of a voltage level comparator, a triac, and so forth.

In case of using the voltage level comparator, an alternating current is received from the primary side or the secondary side of the voltage transformer of each of the rectifying circuits 40 and is then compared with a specified reference signal through the use of the voltage level comparator. A logic signal resulting from the comparison is outputted and differentiated. A pulse signal having a specified period is generated at the timing at which zero cross occurs.

In case of using the triac, a pulse signal can be generated by confirming a change in the polarity of the alternating current at the primary side or the secondary side of the voltage transformer through the use of the triac.

Each of the controllers 30 includes a synchronizing signal processing unit 31, a control unit 32 and a switch 33. The synchronizing signal processing unit 31 is configured to receive and process the synchronizing signal generated by each of the synchronizing signal generators 20. Then the synchronizing signal processing unit 31 transfers the synchronizing signal to the control unit 32. Responsive to the synchronizing signal, the control unit 32 generates a synchronized PWM control signal and transfers the synchronized PWM control signal to the switch 33. The switch 33 is arranged between each of the rectifying circuits 40 and each of the light sources 10. In response to the synchronized PWM control signal, the switch 33 causes each of the light sources 10 to flicker. As the switch 33, it is possible to use a semiconductor switch such as a triac, a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or an IGBT (Insulated-Gate Bipolar Transistor).

The PWM switching frequency is preferably from 100 Hz to 1 kHz. This is because, if the PWM switching frequency is less than 100 Hz, a user may feel a blinking phenomenon. The duty cycle is preferably from 10% to 85%. This is because, if the duty cycle exceeds 85%, the effect of improving the apparent brightness becomes trivial.

The aforementioned frequency range is presented for application to a luminaire for human beings and may vary depending on the application fields. For example, it is reported that, in case of fish-luring lamps, a fish anesthetizing effect is attained only when using a light source flickering at a several-second interval.

Each of the controllers 30 further includes a feedback unit 34. The feedback unit 34 is connected to each of the light sources 10 and is configured to detect the load state of each of the light sources 10 and transfer the detected load state to the control unit 32.

Fig. 4 is a block diagram of an energy saving lighting system according to another embodiment of the present invention. Referring to Fig. 4, the present embodiment differs from the embodiment shown in Fig. 3 in terms of a method of generating a synchronizing signal and transferring the synchronizing signal to a control circuit. Description will be made only on the differing points.

In the present embodiment, a clock pulse generator is used as a synchronizing signal generator 21. The clock pulse generator is configured to generate a signal called a clock pulse at a specified time interval. The clock pulse generator can be formed by combining a crystal oscillator and an unstable multi-vibrator. The clock pulse generated in the clock pulse generator is transferred to the synchronizing signal processing unit 31 of each of the controllers 30 through a plurality of signal lines.

Fig. 5 is a block diagram of an energy saving lighting system according to a further embodiment of the present invention. In the present embodiment, a synchronizing signal generated in a synchronizing signal generator 22 is transferred to a signal synthesizing unit 23. The signal synthesizing unit 23 is configured to load the synchronizing signal onto a power supply line. The synchronizing signal thus loaded is separated from the power supply line by a synchronizing signal extracting unit 24 and is transferred to the synchronizing signal processing unit 31 of each of the controllers 30.

Fig. 6 is a block diagram of an energy saving lighting system according to a still further embodiment of the present invention. In the present embodiment, a synchronizing signal generated in a synchronizing signal generator 25 is transferred to the synchronizing signal processing unit 31 through wireless communication modules respectively installed in the synchronizing signal generator 25 and each of the controllers 30. The synchronizing signal generator 25 is configured to load the synchronizing signal onto a carrier signal and send them to the synchronizing signal processing unit 31. In each of the controllers 30, the synchronizing signal is separated from the carrier signal through the use of a filter. Thereafter, the synchronizing signal is transferred to the synchronizing signal processing unit 31.

Next, description will be made on a case where the pulse width modulation switching frequency is a dual frequency.

By the pulse width modulation switching frequency being a dual frequency, it is meant that each of the light sources is repeatedly turned on and off by a first switching frequency and is repeatedly turned on and off by a second switching frequency which is smaller than the first switching frequency. For example, the first switching frequency may be from 120 Hz to 150 Hz. The second switching frequency may be from 5 Hz to 17 Hz. The second switching frequencyis set to keep the on-duration of the light sources long and the off-duration of the light sources short. Consequently, the pulse wave is transformed into a shape in which the intermediate portion of the pulse wave is partially removed. If the pulse width modulation switching frequency is a dual frequency, there is provided an effect that the apparent brightness gets improved.

Next, brief description will be made on a theoretical basis that the apparent brightness is improved by using the dual frequency as the pulse width modulation switching frequency.

Pursuant to the Mach band effect, the apparent brightness is not a mere intensity function. When observing a border between two regions differing in brightness, a human feels that the region having lower brightness is darker and further that the region having higher brightness is brighter. Use of the Mach band effect makes it possible to increase the apparent brightness felt by a human and to drive the light sources in the frequency region in which a human cannot feel the flickering of the light sources.

Fig. 7 is a diagram for explaining a pulse form in case where the pulse width modulation switching frequency is a dual frequency. Fig. 8 is a diagram for explaining an improvement in apparent brightness in case where the pulse width modulation switching frequency is a dual frequency. The upper image in Fig. 8 is an example in which the light sources are driven by a direct current. The middle image in Fig. 8 is an example in which the light sources are PWM-driven by a single frequency. The lower image in Fig. 8 is an example in which the light sources are PWM-driven by a dual frequency.

As can be seen in Fig.8, the middle image is felt brighter than the upper image. The lower imaged is felt brighter than the middle image.

Since a spatial region and a time region have the same tendency in terms of visual feeling, it can be noted that the apparent brightness is further improved if the pulse width modulation switching frequency is a dual frequency.

It is to be understood that the embodiments described above are illustrative and not limitative in all respects. The scope of the present invention is not defined by the foregoing description but is defined by the appended claims. All changes and modifications derived from the claims and its equivalents shall be construed to fall within the scope of the present invention.

Claims

An energy saving lighting system, comprising:

a plurality of light sources irradiating light on the same region;

a synchronizing signal generator configured to generate a synchronizing signal for synchronizing flickering timings of the light sources; and

a plurality of controllers installed in a corresponding relationship with the light sources, the controllers configured to synchronize the flickering timings of the light sources by receiving the synchronizing signal and PWM (Pulse Width Modulation)-controlling the light sources in response to the synchronizing signal to enhance the apparent brightness of the region irradiated by the a plurality of light sources.
The energy saving lighting system of claim 1, wherein the synchronizing signal generator is installed between each of the light sources and an AC power source for supplying an alternating current to the light sources, the synchronizing signal generator configured to generate the synchronizing signal by sensing a phase change of the alternating current.
The energy saving lighting system of claim 2, wherein the synchronizing signal generator is a zero-cross detector configured to generate the synchronizing signal by detecting a moment at which an instantaneous value of a voltage of the alternating current becomes zero.
The energy saving lighting system of claim 1, wherein the synchronizing signal is transferred to the controllers through wireless modules installed in the synchronizing signal generator and the controllers.
The energy saving lighting system of claim 1, wherein the synchronizing signal is loaded onto and transmitted through power supply lines leading to the light sources and is then extracted from the power supply lines and transferred to the controllers by a power line transmission method.
The energy saving lighting system of claim 1, wherein the synchronizing signal is transferred to the controllers through independent signal lines installed between the synchronizing signal generator and the controllers.
The energy saving lighting system of claim 1, wherein the light sources are controlled at a pulse width modulation switching frequency of from 100 Hz to 1 kHz and at a duty cycle of from 10% to 85%.
The energy saving lighting system of claim 1, wherein the light sources are controlled at a pulse width modulation switching frequency and at a duty cycle of from 10% to 85%, the pulse width modulation switching frequency being a dual frequency including a first switching frequency of from 100 Hz to 1 kHz and a second switching frequency lower than the first switching frequency.
The energy saving lighting system of claim 8, wherein the second switching frequencyis set to keep on-duration of the light sources longer than off-duration of the light sources.
The energy saving lighting system of claim 1, wherein the light sources are a pair of headlights of a vehicle.