Patent Publication Number: US-9423774-B2

Title: Electronic timepiece including light emitting section

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an electronic timepiece including a light emitting section. 
     2. Description of Related Art 
     Conventionally, there have been electronic timepieces which include illumination functions of illuminating display surfaces so that users can surely confirm time and various types of information visually in dark places such as outdoors and bed rooms at night. Such electronic timepieces have configurations for detecting user&#39;s operations and turning on light emitting elements for predetermined periods of time, the user&#39;s operations including pressing of predetermined push button switches and inclination of wristwatches at predetermined angles in dark places where light amounts detected by light amount sensors are predetermined reference values or less. 
     As a technique for improving visibility by such illumination functions, Japanese Patent Laid-Open Publication No. 2004-53381 discloses a technique of efficiently illuminating an entire display surface by providing a frame-like light-permeable member which has fine irregularities on the outer circumference of the display surface, reflecting and diffusing, with the fine irregularities, light emitted from a light emitting element which is provided inside the light-permeable member, and generating circular illumination. 
     However, light emitting elements having higher brightness have been used in recent years, and there has been a problem that user&#39;s visibility is disturbed since the user feels the light dazzling when such light emitting elements are suddenly turned on in dark places. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an electronic timepiece which is gentle to user&#39;s eyes and can ensure good visibility. 
     In order to achieve the above object, according to one aspect of the present invention, there is provided an electronic timepiece, including: a display section which displays time information; a light emitting section which illuminates a display surface of the display section by emitting light; and a light emitting control section which performs control to turn on the light emitting section by gradually increasing a light emitting amount of the light emitting section to a peak value in a predetermined brightening time according to a predetermined light emitting condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will become more fully understood from the detailed description given hereinafter and the appended drawings which are given byway of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein: 
         FIG. 1  is a sectional view of an electronic timepiece in an embodiment; 
         FIG. 2  is a block diagram showing a functional configuration of the electronic timepiece; 
         FIG. 3  is a view for explaining a light emitting pattern of light emitting element of an illumination section; 
         FIG. 4  is a view showing examples of transition in light emitting amount of the light emitting element; 
         FIG. 5  is a view for explaining light emitting control when a hand is rotated; and 
         FIG. 6  is a flow chart showing a control procedure of illumination control processing. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, an embodiment of the present invention will be described on the basis of the drawings. 
       FIG. 1  is a sectional view of an electronic timepiece  1  in the embodiment of the present invention. 
     The sectional view shows a cross section which is through the center of the electronic timepiece  1  and orthogonal to the display surface. 
     The electronic timepiece  1  is an analog electronic timepiece which rotates a plurality of hands  61  to  63  and displays date and time. 
     The electronic timepiece  1  includes an annular frame  6 ; an annular parting plate  9  which contacts the inner wall of the frame  6 ; a face  3 ; a second hand  61 , a minute hand  62  and an hour hand  63  (hereinafter, also referred to as hands  61  to  63  together) which are provided so as to be rotatable on the display surface of the face  3 ; a transparent watch glass  8  which covers the display surface of the face  3  and the hands  61  to  63 ; a substrate  4  and a module  5  which are provided at the opposite side of the display surface of the face  3 ; a back cover  7  which contains therein the substrate  4  and the module  5  together with the frame  6 ; a light emitting element  55   a  (light emitting section); a wiring  55   b  and such like. 
     Various scales and marks for the hands  61  to  63  to indicate time and various types of information are provided on the display surface side of the face  3 . 
     The face  3  is also provided with a solar panel to generate electric power according to the amount of incident light. 
     The face  3  and the hands  61  to  63  form a display section. 
     The substrate  4  is provided with various electronic components and electronic circuits according to operations of the electronic timepiece  1 . 
     The electric power is supplied from the solar panel, a secondary cell and such like to the substrate  4  to control various operations, count time and store setting data and such like. 
     The module  5  includes various configurations according to hand operations, the secondary cell of a power supply section  50  (see  FIG. 2 ) and such like, and the module  5  is disposed at an appropriate position. 
     The module  5  is connected to the substrate  4  via a wiring (not shown in the drawings) to input control signals and input/output the electric power. 
     The light emitting element  55   a  is provided in the concave portion provided on the inner lateral surface of the annular parting plate  9 , and illuminates the hands and face  3  from a lateral side. 
     An LED (Light Emitting Diode) is used as the light emitting element  55   a , for example. 
     The concave portion and the light emitting element  55   a  are provided in the 6 o&#39;clock side of the face  3  though the positions thereof are not especially limited. 
     The light emitting element  55   a  is connected to the substrate  4  via the wiring  55   b , and emits light at the light amount corresponding to the current-carrying state of the wiring  55   b.    
       FIG. 2  is a block diagram showing a functional configuration of the electronic timepiece  1  in the embodiment of the present invention. 
     The electronic timepiece  1  includes a CPU  41  (Central Processing Unit) (light emitting control section), a ROM  42  (Read Only Memory), a RAM  43  (Random Access Memory), an oscillation circuit  44 , a frequency divider  45 , a clock circuit  46 , an external light amount detecting section  47  (external light detecting section), a drive circuit  48  (operation detecting section and drive control section), a power supply section  50 , an illumination section  55 , a driver thereof  56 , a notification section  57 , a driver thereof  58 , an operation section  59 , stepping motors  51  and  52 , gear train mechanisms  53  and  54 , a second hand  61 , a minute hand  62 , an hour hand  63  and such like. 
     The CPU  41  performs various types of arithmetic processing and integrally controls the entire operation of the electronic timepiece  1 . 
     The CPU  41  loads a control program read out from the ROM  42  into the RAM  43  and performs processing according to various operations such as time display and counting and display of stopwatch. 
     The ROM  42  is a mask ROM, a rewritable non-volatile memory or the like and stores control programs and initial setting data which are stored in advance. 
     The control programs include an illumination control program  421  to perform various types of control processing according to on/off of lighting of the illumination section  55 . 
     The RAM  43  is a volatile memory such as a SRAM and a DRAM, stores temporal data by providing a memory space for working to the CPU  41  and stores various types of setting data. 
     The oscillation circuit  44  generates and outputs predetermined frequency signals. 
     A crystal oscillator is used as the oscillation circuit  44 , for example. 
     The frequency divider  45  divides the frequency signals input from the oscillation circuit  44  into frequency signals used by the clock circuit  46  and the CPU  41 , and outputs the signals. 
     The frequency of the output signals may be changeable on the basis of the setting by the CPU  41 . 
     The signals may also be directly output maintaining the frequency thereof in the oscillation circuit  44 . 
     The clock circuit  46  counts the current date and time by counting the number of input signals and adding the number to an initial value. 
     The clock circuit  46  may change the value to be stored in the RAM by software, or may include a dedicated counter circuit. 
     The drive circuit  48  outputs pulses of drive voltage waveform (drive pulses) at an appropriate timing and width to the stepping motors  51  and  52  on the basis of control signals input from the CPU  41  to move the hands  61  to  63 . 
     The drive circuit  48  can change the pulse width of drive pulse according to the state of electronic timepiece  1  and such like. 
     When a control signal to drive a plurality of hands at the same time is input, the drive circuit  48  can slightly shift the respective output timings of drive pulses so as to reduce the load peak. 
     The stepping motor  51  rotates the second hand  61  via the gear train mechanism  53  disposing a plurality of gears. The stepping motor  52  rotates the minute hand  62  and the hour hand  63  in conjunction with each other via the gear train mechanism  54 . 
     The numbers of rotation of the respective hands per step of the stepping motors  51  and  52  are determined by the arrangement of gears in the gear train mechanisms  53  and  54 , respectively. 
     For example, here, the gear train mechanism  53  is configured so that the secondhand  61  is rotated 6 degrees per step of the stepping motor  51 , and the gear train mechanism  54  is configured so that the minute hand  62  is rotated 1 degree per step of the stepping motor  52 . 
     According to the configuration of the gear train mechanism  54 , the hour hand  63  is rotated in conjunction with the minute hand  62  at the rotation angle of 1/12 with respect to the rotation of the minute hand  62 . 
     Accordingly, the minute hand  62  makes one rotation on the display surface of the face  3  in 60 minutes by rotating 1 degree per 10 seconds, while the hour hand  63  rotates 30 degrees on the display surface of the face  3  in 60 minutes. 
     Then, the hour hand  63  makes one rotation on the display surface of the face  3  while the minute hand  62  makes 12 rotations in 12 hours. 
     The power supply section  50  supplies electric power according to the operation of the electronic timepiece  1  to the respective sections at a predetermined voltage. 
     Here, a solar battery and a secondary cell are used as the power supply section  50 . 
     The solar panel of the face  3  generates an electromotive force by the incident light and supply the electric power to the sections such as the CPU  41 . When excess electric power is generated, the electric power is charged in the secondary cell. 
     On the other hand, when the electric power which can be generated from the incident light amount from outside to the solar panel is less than the electric power to be consumed, the electric power is supplied from the secondary cell. 
     The power supply section  50  also supplies electric power directly to the illumination section  55  and the notification section  57  on the basis of the control signal from the CPU  41 . 
     The external light amount detecting section  47  measures the amount of incident light to the solar panel. 
     The external light amount detecting section  47  obtains the incident light amount from the amount of electromotive force by the solar panel, for example, and outputs the measurement value as the detected light amount to the CPU  41  at a predetermined sampling rate. 
     Alternatively, the external light amount detecting section  47  may be configured to include one or a plurality of comparators to compare each reference voltage with the electromotive force by the comparator and output the voltage signal indicating the magnitude relation therebetween to the CPU  41 . 
     The operation section  59  receives the input operation from user and outputs an electric signal corresponding to the input operation as an input signal to the CPU  41 . 
     The operation section  59  includes push button switches and a crown switch, for example. 
     The notification section  57  performs a predetermined notification operation to the user such as generation of buzzer sound and vibration. 
     For example, the notification section  57  includes a piezoelectric element and a vibration plate, and can generate a beep sound by applying a voltage of a desired audible field frequency to the piezoelectric element via the driver  58  to vibrate the piezoelectric element. 
     Alternatively, the notification section  57  includes a weighted motor, for example, and can generate vibration by rotating the motor at a predetermined frequency. 
     As the driver  58 , a driver corresponding to the configuration of notification section  57  which performs the above notification operation is provided and outputs a drive signal of a predetermined voltage or electric current to the notification section  57 . 
     The illumination section  55  includes the light emitting element  55   a , and illuminates the display surface of face  3  and the hands  61  to  63  by light emitting of the light emitting element  55   a.    
     The driver  56  controls the output of electric power supplied from the power supply section  50  to the light emitting element  55   a  on the basis of the control signal from the CPU  41 . 
     The driver  56  can vary the light emitting amount of light emitting element  55   a  in multiple levels by PWM (Pulse Width Modulation). 
     The maximum light emitting amount of the light emitting element  55   a  is determined by a resistance value of resistance element provided serially to the light emitting element  55   a  in the illumination section  55 . 
     The control of illumination operation by the light emitting element  55   a  will be described in detail below. 
     The CPU  41 , ROM  42 , RAM  43 , oscillation circuit  44 , frequency divider  45 , clock circuit  46 , external light amount detecting section  47 , drive circuit  48  and such like are provided as a one chip to the substrate  4 , and the stepping motors  51  and  52 , gear train mechanisms  53  and  54  and secondary cell of power supply section  50  are provided inside the module  5 , for example. 
     The notification section  57  and the operation section  59  may be appropriately provided to positions appropriate for notification operation to the user and reception of user&#39;s operation, respectively. 
     Next, the illumination operation by the illumination section  55  will be described. 
     In the illumination section  55  of the embodiment, the power supply from the power supply section  50  is turned on and off by the control of the CPU  41 , and thereby the on/off of lighting of the light emitting element  55   a  is controlled. 
     The illumination section  55  includes a switching element such as an FET in the power supply circuit from the power supply section  50  to the light emitting element  55   a , for example. 
     The CPU  41  outputs a control signal for applying a predetermined on-voltage Von (for example, on-voltage Von&gt;0 in a case of n-type FET) to the gate electrode of FET, thereby the electric current flows through the light emitting element  55   a , and the light emitting element  55   a  emits light. 
     On the other hand, the electric current does not flow through the light emitting element  55   a  by the off-voltage Voff (off-voltage Voff=0 in a case of n-type FET) being output to the gate electrode of FET, and the light emitting element  55   a  is turned off. 
       FIG. 3  is a view for explaining a light emitting pattern of the light emitting element  55   a  of the illumination section  55  in the electronic timepiece  1  of the embodiment. 
     The CPU  41  adjusts the light emitting amount per unit time by pulse width modulation (PWM) by varying the period of time for turning on the power supply, that is, the period of time for which the electric current flows through the light emitting element  55   a  (duty ratio) in 16 stages per 16 cycles 1/1024 seconds (unit time) on the basis of a clock signal input from the frequency divider  45 , here, a 16.384 kHz signal, for example. 
     Accordingly, the unit time is appropriately determined in a range shorter than the time for which a person can perceive the blinking of ordinary light. 
     When the instruction to turn on the light emitting element  55   a  is obtained from the user&#39;s input operation to the operation section  59 , the CPU  41  of the electronic timepiece  1  performs PWM control to gradually increase the light emitting amount of the light emitting element  55   a  to a predetermined maximum light emitting amount in a predetermined period of time. 
     After the light is emitted at the maximum light emitting amount over a preset duration time, the CPU  41  gradually decreases the light emitting amount of the light emitting element  55   a  to turn off the light in a predetermined period of time. 
     At this time, the predetermined period of time (brightening time) according to gradual increase in the light emitting amount when the light is turned on may be the same as or different from the predetermined period of time (darkening time) according to the gradual decrease of the light emitting amount when the light is turned off. 
     The pattern of gradual increase (gradual decrease) of the light emitting amount in the predetermined period of time may be appropriately set. 
     That is, the change rate of the duty ratio may be constant or may be varied at a predetermined pattern in the predetermined period of time. 
       FIG. 4  is a view showing transition examples of light emitting amount of the light emitting element  55   a.    
     In one of the examples, the light emitting amount is gradually increased to the maximum light emitting amount L 1  (peak value) in time T 1  (brightening time) from the start of lighting operation by the CPU  41 , the light is emitted at the maximum light emitting amount L 1  over a duration time D 1 , and thereafter, the light emitting amount is gradually decreased to turn off the light in the time T 1  (darkening time). In the other of the examples, the light emitting amount is gradually increased to the maximum light emitting amount L 2  (&gt;L 1 ) in time T 2  (&lt;T 1 ), the light is emitted at the maximum light emitting amount L 2  (&gt;L 1 ) over duration time D 2  (&lt;D 1 ), and thereafter the light emitting amount is gradually decreased to turn off the light in the time T 2 . 
     Such a plurality of patterns of light on/off controls may be automatically selected according to the condition (light emitting condition) and such like when light is turned on instead of being selected by user&#39;s setting in advance. 
     Here, either one is selected according to the incident light amount (detected light amount) detected by the external light amount detecting section  47 . 
     For example, the setting can be such that, when a lighting instruction is obtained by the input operation to the operation section  59  by the user, if the light amount detected by the external light amount detecting section  47  at the present timing is a predetermined reference value or more, the maximum light emitting amount is set to be L 2  and the duration time is set to be D 2 , and if the detected light amount is less than the reference value, the maximum light emitting amount is set to be L 1  and the duration time is set to be D 1 . 
     Alternatively, as another example of selecting method (light emitting condition) for a plurality of patterns of light on/off controls, the setting can be such that, when a lighting instruction is obtained from the input operation to the operation section  59  by the user, the lighting pattern of maximum light emitting amount L 1 , duration time D 1  and time T 1  according to gradual increase/decrease is selected, and when the lighting instruction is obtained from an internal operation such as an alarm notification operation and a timer notification operation, a lighting pattern of the maximum light emitting amount L 2 , duration time D 2  and time T 2  according to gradual increase/decrease is selected. 
     The adjustment of light amount by PWM control may be temporarily interrupted. 
       FIG. 5  is a view for explaining light emitting control during hand rotation operation. 
     Here, the output of voltage pulse according to PWM control is stopped during a drive pulse output period Dm (voltage Vm) to output drive pulses to the stepping motors  51  and  52  and a predetermined waiting period Dd after the end of the drive pulse output period Dm. 
     The drive pulse output period Dm and the waiting period Dd are collectively called an operation period of stepping motors  51  and  52  (that is, hands  61  to  63 ). 
     In the PWM control, electromagnetic noise is generated due to the frequent change in voltage and electric current of circuit according to on/off of the power supply. 
     Since the stepping motors  51  and  52  control rotor&#39;s rotation by using magnetic field, it is preferable to reduce electromagnetic noise generated at close range. 
     In a case where rotation of the stepping motors  51  and  52  is detected in the electronic timepiece  1 , there is a detection method using a back electromotive force (inductive current) generated at a stator-side coil when the motion of rotor for each of the stepping motors  51  and  52  is stopped. 
     At this time, when electromagnetic noise is superposed on minute back electromotive force, the detection accuracy of the back electromotive force is lowered. 
     Accordingly, the detection accuracy can be improved by interrupting the PWM control from tm 1  to td 2  including the waiting period Dd as a detection period of back electromotive force, the tm 1  being the start timing to output drive pulses to the stepping motors  51  and  52 , and the td 2  being the end of detection of back electromotive force after the output of drive pulse is ended. 
     In the electronic timepiece  1  of the embodiment, the rotor&#39;s rotation is detected by the drive circuit  48  measuring the back electromotive force. 
     When the rotor&#39;s rotation cannot be detected within a predetermined period of time, the drive circuit  48  may be configured to drive the stepping motors  51  and  52  again by outputting drive pulses again at a predetermined interval. 
     Alternatively, the measurement of back electromotive force may be performed by a separately-provided detection section to output the measurement result to the CPU  41  and the drive circuit  48 . 
     Generally, the interruption period is approximately several milliseconds to several tens of milliseconds for one hand. 
     Here, when a control signal for simultaneously rotating a plurality of hands is output from the CPU  41 , in the electronic timepiece  1  of the embodiment, the drive circuit  48  outputs drive pulses by shifting the timings to output the drive pulses to stepping motors corresponding to the respective hands so as not to overlap each other. 
     The waiting period Dd according to the rotation of each of the plurality of hands is set to be continuous with the drive pulse output period Dm of the following hand which is to be continuously rotated. 
     Accordingly, when a plurality of hands are simultaneously rotated, the interrupting period of light emitting by the PWM control becomes long according to the number of hands to be rotated. 
       FIG. 6  is a flow chart showing a control procedure of illumination control processing executed by the CPU  41  in the electronic timepiece  1  of the embodiment. 
     The illumination control processing is activated when a lighting instruction is obtained from the user via the operation section  59  and when a light emitting instruction is generated by an internal operation. 
     When the illumination control processing is started, the CPU  41  obtains the incident light amount which is input from the external light amount detecting section  47  (step S 101 ). 
     The CPU  41  sets the brightening time when turning on light, the darkening time when turning off light, the maximum light emitting amount and the duration time at the maximum light emitting amount on the basis of the obtained incident light amount (step S 102 ). 
     The CPU  41  determines whether or not the present time is in the drive pulse output period Dm for outputting drive pulses to a stepping motor according to the hand rotation or the waiting period Dd according to the operation detection of the stepping motor after the drive pulse output period Dm (step S 103 ). 
     If it is determined that the present time is in the drive pulse output period Dm or the waiting period Dd (step S 103 : YES), the CPU  41  interrupts the output of control signal according to the lighting control of the light emitting element  55   a  to the illumination section  55  (step S 104 ). 
     Then, the processing of CPU  41  shifts to step S 106 . 
     If it is not determined that the present time is in the drive pulse output period Dm or the waiting period Dd (step S 103  NO), the CPU  41  outputs the control signal according to the PWM control for lighting the light emitting element  55   a  at the light emitting amount corresponding to the elapsed time from the start of lighting to the illumination section  55  on the basis of the conditions which were set in step S 102  (step S 105 ). 
     Then, the processing of CPU  41  shifts to step S 106 . 
     When the processing shifts to step S 106 , the CPU  41  determines whether the lighting time of light emitting element  55   a , that is, a total of the above mentioned brightening time, duration time and the darkening time has elapsed (step S 106 ). 
     If it is not determined that the lighting time has elapsed (step S 106 : NO), the processing of CPU  41  returns to step S 103 . If it is determined that the lighting time has elapsed (step S 106 : YES), the CPU  41  ends the illumination control processing. 
     As described above, the electronic timepiece  1  of the embodiment formed of the face  3  and the hands  61  to  63  includes the display section which displays time information and the light emitting element  55   a  which illuminates the display surface of the display section by emitting light. In the electronic timepiece  1 , the CPU  41  controls to perform lighting by gradually increasing the light emitting mount of the light emitting element  55   a  to the maximum light emitting amount in a predetermined brightening time according to a predetermined light emitting condition. 
     Thus, in the electronic timepiece  1 , since the light emitting element  55   a  does not suddenly emit light at the maximum light emitting amount in a dark place, it is possible to reduce the dazzle to be felt by the user, and the electronic timepiece  1  can be gentle to user&#39;s eyes and ensure good visibility. 
     Especially, even if the maximum light emitting amount of the light emitting element  55   a  is more than conventional maximum light emitting amounts to improve visibility, the user does not feel the light dazzling more than necessary. 
     Since the CPU  41  makes the driver  56  vary the light emitting amount of the light emitting element  55   a  by PWM control, it is not necessary to add a hardware configuration for changing light amount, and the light amount can be changed easily and flexibly. 
     It is also possible to suppress the cost increase according to the manufacturing of the electronic timepiece  1 . 
     The CPU  41  varies at least one of the maximum light emitting amount and the brightening time according to various light emitting conditions including the surrounding environment such as the incident light amount from outside when the light is turned on and the type of instruction such as lighting instruction according to user&#39;s operation or lighting instruction according to an internal operation such as alarm notification. Thus, it is possible to effectively use the light of light emitting element  55   a  by lighting the light emitting element  55   a  by an appropriate lighting method or light amount according to the situation. 
     The electronic timepiece  1  includes the external light amount detecting section  47 , and can detect the incident light amount from outside by detecting the electromotive force of solar panel and such like. The CPU  41  can set the maximum light emitting amount to be larger and the brightening time to be shorter as the detected light amount is larger. 
     By the setting, it is possible to shorten the brightening time and set a sufficient light amount to enable the user perceive the lighting state compared to the incident light amount at an environment where the user does not feel the light dazzling. 
     Furthermore, it is possible to suppress a part or all of the increase in power consumption due to the increase in maximum light emitting amount by shortening the brightening time. 
     The electronic timepiece  1  includes the operation section  59  which receives the user&#39;s operation. In a case where the instruction to light the light emitting element  55   a  is obtained from the operation section  59 , the CPU  41  can set the brightening time longer than that of the case where the light emitting element  55   a  is lighted according to the internal operation in the electronic timepiece  1  such as alarm notification and timer time elapse notification. 
     Thus, it is possible to change the brightening time between the case of operation, that is, the case where the user has been seeing the display screen when the light emitting element  55   a  is lighted and the case where the user is not seeing the display screen when the lighting of the light emitting element  55   a  is started according to the internal operation. 
     In a case where the notification operation itself is significant rather than the display content, it is possible to notify the user more effectively by increasing the light emitting amount rapidly. 
     The electronic timepiece  1  is an analog electronic timepiece which includes a display section including a plurality of hands  61  to  63  and stepping motors  51  and  52  for rotating the hands  61  to  63 , and the CPU  41  interrupts the PWM control during the operation period for rotating any one of the plurality of hands  61  to  63  by any one of the stepping motors  51  and  52 . 
     Thus, since it is possible to suppress the generation of the electromagnetic noise due to the change in electric current following the on/off of switch according to PWM control, it is possible to surely operate the stepping motors  51  and  52  and surely confirm the operations of stepping motors  51  and  52 . 
     Since the CPU  41  turns off the light emitting element  55   a  during the interruption of PWM control, it is possible to suppress the power consumption compared to the case where the light emitting element  55   a  is lighted, and suppress the uncomfortable feeling compared to the case of increasing the light emitting amount even in a case where the interruption of PWM control is long and the user can visually confirm the blinking. 
     The drive circuit  48  measures the back electromotive force after output of the drive pulse to each of the stepping motors  51  and  52  and detects the rotation operation of rotor. 
     Since the detection period of rotation operation of rotor is included in the above-mentioned operation period for each of the stepping motors  51  and  52 , it is possible to prevent the superposition of electromagnetic noise onto the weak back electromotive force and surely confirm the rotation operation of rotor. 
     The drive circuit  48  controls timings to drive the stepping motors  51  and  52  on the basis of control signals from the CPU  41 . 
     The stepping motor  51  rotates the second hand  61  and the stepping motor  52  rotates the minute hand  62  and the hour hand  63  independently from the second hand  61 . 
     In a case where the timings to rotate at least two hands overlap each other every hour on the hour, for example, the drive circuit  48  shifts the timings so that the operation periods of stepping motors  51  and  52  for rotating the at least two hands, that is, the output periods of drive pulse do not overlap each other, and drives the stepping motors  51  and  52  in order. Accordingly, it is possible to prevent the great load from being placed at one time. 
     In such case, the PWM control is interrupted over the respective operation periods. 
     As described above, the operation periods of stepping motors for rotating at least two hands are set to be continuous with each other in a case where the rotation timings of the at least two of the hands  61  to  63  overlap each other. Thus, the interruption periods of the PWM control are set together into a whole. 
     Accordingly, the hand operation is not unnaturally delayed and the setting of the interruption period of PWM control is not complicated. 
     The CPU  41  gradually decreases the light emitting amount in the predetermined darkening time to turn off the light after making the light emitting element  55   a  emit the light at maximum light emitting amount over the predetermined duration time. 
     Accordingly, it is possible to not only reduce the dazzle when increasing the light amount, but also adjust light naturally when increasing or decreasing light. 
     The present invention is not limited to the above embodiment and various changes can be made. 
     For example, the PWM control needs not be interrupted during the drive pulse output periods to the stepping motors  51  and  52  in a case where the operations of stepping motors  51  and  52  are not detected, in a case where the influence of electromagnetic noise can be reduced or avoided by performing the detection with a method other than the back electromotive force such as encoder or in a case where the influence of the electromagnetic noise needs not be considered due to the location of the components in the module  5  or an electromagnetic noise shield member. 
     On the other hand, instead of or in addition to when the stepping motors  51  and  52  are operated, the PWM control can be temporarily interrupted also in a case of performing various operations which possibly generates bad influence of electromagnetic noise such as reception of standard waves according to acquisition of date and time information from outside and radio wave reception from positioning satellites. 
     During the interruption period of PWM control, the light emitting element  55   a  may be maintained to be turned on instead of being maintained to be turned off. 
     In such case, either one of turned-off state or turned-on state may be further selected according to the light amount immediately before the interruption. 
     The above embodiment has been described by illustrating a case where the hands and the face  3  are illuminated from a lateral side by LED illumination; however the light emitting element  55   a  is not limited to the LED and may be others such as an organic light emitting diode (OLED), for example. 
     The present invention can also be applied to a backlight which illuminates the face  3  not by emitting light from a lateral side but by making an organic EL emit light on the display surface of face  3  or from the opposite side of the display surface of the light permeable face  3 . 
     The above embodiment has been described for an analog electronic timepiece using a plurality of hands; however, the present invention may be applied to a digital electronic timepiece which performs digital display using an LCD or the like. 
     The above embodiment has been described for the electronic timepiece  1 , as an analog electronic timepiece, which is provided with the second hand  61 , and the minute hand  62  and hour hand  63  rotated in conjunction with each other; however, all the hands  61  to  63  may be rotated independently, or all the hands  61  to  63  may be rotated in conjunction with each other. 
     The number of hands is not limited to three, and may be another number. 
     Similarly, the number of stepping motors is determined according to the number of hands which are independently rotated. 
     The present invention may also be applied to an electronic timepiece which rotates hands by a means other than stepping motors. 
     In the embodiment, the light emitting amount is adjusted by PWM control; however, the adjustment can be performed by changing the electric current and voltage input from the power supply section  50  to the light emitting element  55   a.    
     For example, the resistance value of resistance element provided in series to the light emitting element  55   a  may be changeable or a plurality of resistance elements having different resistance values may be provided in parallel to each other so that any one of the resistance elements is selectively connected to the light emitting element  55   a  by a switching element to change the partial pressure to be applied to the light emitting element  55   a.    
     In the embodiment, the light emitting amount is larger as the detected light amount of external light amount detecting section  47  is larger; however, the light emitting amount can be smaller as the detected light amount is larger, or the light emitting amount may not be changed by the detected light amount. 
     The light emitting amount can be set not only in two steps but also in arbitrary steps or may be set to be continuous. In a case where the light emitting amount is set continuous, for example, it is possible to perform calculation every time by storing a conversion equation to calculate a setting value of maximum light emitting amount or the like by using, as a variable, the incident light amount or the electromotive force of solar panel. 
     In the embodiment, the maximum light emitting amount, the brightening time and such like are set according to the detected light amount by the external light amount detecting section  47  and the input operation to the operation section  59 ; however, the setting may be performed by using other light emitting conditions as a variable such as the inclination angle of display surface detected by an inclination sensor and the movement status of electronic timepiece  1  detected by an acceleration sensor. 
     Alternatively, the setting may be different between a case of time display and a case of other functional display such as a stopwatch display even for a same operation input by a user. 
     In the embodiment, the electronic timepiece  1  is operated by power supply from solar electric generation and a secondary cell; however, a primary cell such as a general button type cell may be used. 
     In this case, for example, an external light amount detecting section  47  which is independent by using a photodiode or the like may be provided unrelated to solar electric generation. 
     The embodiment has been described for a case where only one light emitting element  55   a  is provided; however, a plurality of light emitting elements  55   a  may be provided. 
     In this case, the light emitting amounts of the light emitting elements  55   a  may be controlled together by a single control signal or switching element, or separate control signals may be output to the individual switching elements from the CPU  41 . 
     In the embodiment, the light emitting amount is gradually increased when the light is turned on and the light emitting amount is gradually decreased when the light is turned off; however, since the change in light amount when the light is turned off is not related to the reduction of dazzle for a user, the light may be turned off by immediately break down the power supply. 
     The embodiment has been described by taking, as an example, a light emitting pattern with a large maximum light emitting amount and a short brightening time, and a light emitting pattern with a small maximum light emitting amount and a long brightening time; however, the light emitting pattern is not limited to them. 
     Only one of the maximum light emitting amount and the brightening time may be changed, or the combination of maximum light emitting amount and brightening time in a pattern may be opposite, that is, the brightening time may be short when the maximum light emitting amount is small, for example. 
     The other detailed specifics such as specific configurations, shapes, locations, operations and procedures shown in the embodiment can be appropriately changed within the scope of the present invention. 
     Though several embodiments of the present invention have been described above, the scope of the present invention is not limited to the above embodiments, and includes the scope of inventions, which is described in the scope of claims, and the scope equivalent thereof. 
     The entire disclosure of Japanese Patent Application No. 2014-132495 filed on Jun. 27, 2014 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety.