Electric discharge lamp device

Abstract

An electric discharge lamp device has a lighting start voltage storage circuit for storing a lamp voltage immediately after the start of lighting of a lamp, and a change detection circuit for detecting a change in the lamp voltage by subtracting the lamp voltage immediately after the start of lighting of the lamp from the lamp voltage detected currently. The electric power supplied to the lamp is controlled based upon the change in the lamp voltage.

1. An electric discharge lamp device comprising:
 lamp voltage detection means for detecting a lamp voltage and producing a lamp voltage signal:  
 storage means for storing the lamp voltage signal produced from a lamp voltage detected immediately after a start of lighting a lamp; and  
 change detection means for detecting a change in the lamp voltage by subtracting the lamp voltage signal stored in the storage means from the lamp voltage signal produced from a lamp voltage detected after the lamp voltage signal is stored in the storage means; and,  
 control means for controlling electric power supplied to the lamp based upon the change detected by the change detection means.  
 
     
     
       2. An electric discharge lamp device as in  claim 1 , wherein the storage means stores the lamp voltage signal after an elapse of a predetermined period of time from the start of lighting the lamp as the lamp voltage detected immediately after the start of lighting the lamp. 
     
     
       3. An electric discharge lamp device as in  claim 2 , wherein the predetermined period of time is not longer than 6 seconds. 
     
     
       4. An electric discharge lamp device as in  claim 3 , wherein the lamp voltage signal stored in the storage means is a minimum voltage value in the predetermined period of time. 
     
     
       5. An electric discharge lamp device as in  claim 1 , further comprising:
 a timer circuit for controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting,  
 wherein the timer circuit gradually decreases the electric power supplied to the lamp depending upon the elapse of time from when the change detected by the change detection means has exceeded a predetermined value to be shifted to the electric power that is supplied to the lamp in a stable state.  
 
     
     
       6. An electric discharge lamp device as in  claim 5 , wherein the timer circuit gradually decreases the electric power supplied to the lamp irrespective of the change of the lamp voltage signal after elapse of a predetermined period of time from the start of lighting. 
     
     
       7. An electric discharge lamp device as in  claim 6 , wherein the predetermined period of time is set depending upon a lamp turn-off time in which the lamp is maintained turned off. 
     
     
       8. An electric discharge lamp device as in  claim 1 , further comprising:
 a timer circuit for controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting,  
 wherein the timer circuit gradually decreases the electric power supplied to the lamp depending upon the elapse of time from when the change detected by the change detection means has exceeded a predetermined value or from when a lamp voltage has exceeded the predetermined value, whichever is earlier, so as to be shifted to the electric power that is supplied to the lamp in a stable state.  
 
     
     
       9. An electric discharge lamp device as in  claim 1 , wherein the electric discharge lamp device is a mercury-free lamp device. 
     
     
       10. An electric discharge lamp device as in  claim 9 , wherein the mercury-free lamp device is mounted on a vehicle. 
     
     
       11. An electric discharge lamp device comprising:
 a lamp voltage detection circuit for detecting a lamp voltage and producing a lamp voltage signal;  
 a storage circuit for storing the lamp voltage signal produced from a lamp voltage detected immediately after each start of lighting a lamp; and  
 a change detection circuit for detecting a change in the lamp voltage by subtracting the lamp voltage signal stored in the storage circuit from a lamp voltage signal produced from a lamp voltage detected after the lamp voltage signal is stored in the storage circuit; and  
 a controller for controlling electric power supplied to the lamp based upon the change detected by the change detection circuit.  
 
     
     
       12. An electric discharge lamp device comprising:
 a storage circuit for storing a lamp voltage signal corresponding to a lamp voltage which is detected immediately after a start of lighting a lamp; and  
 a change detection circuit for detecting a change in the lamp voltage by subtracting the lamp voltage signal stored in the storage circuit immediately after the lighting from the lamp voltage signal corresponding to the lamp voltage being detected currently,  
 wherein electric power supplied to the lamp is controlled based upon the change detected by the change detection circuit;  
 wherein the storage circuit stores the lamp voltage signal after an elapse of a predetermined period of time from the start of lighting the lamp as the lamp voltage detected immediately after the start of lighting the lamp, the predetermined period of time not being longer than 6 seconds.  
 
     
     
       13. An electric discharge lamp device as in  claim 12 , wherein the lamp voltage signal stored in the storage circuit is a minimum voltage value in the predetermined period of time. 
     
     
       14. An electric discharge lamp device comprising:
 a storage circuit for storing a lamp voltage signal corresponding to a lamp voltage which is detected immediately after a start of lighting a lamp;  
 a change detection circuit for detecting a change in the lamp voltage by subtracting the lamp voltage signal stored in the storage circuit immediately after the lighting from the lamp voltage signal corresponding to the lamp voltage being detected currently, electric power supplied to the lamp being controlled based upon the change detected by the change detection circuit; and  
 a timer circuit for controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting;  
 wherein the timer circuit gradually decreases the electric power supplied to the lamp depending upon the elapse of time from when the change detected by the change detection circuit has exceeded a predetermined value to be shifted to the electric power that is supplied to the lamp in a stable state;  
 wherein the timer circuit gradually decreases the electric power supplied to the lamp irrespective of the change of the lamp voltage signal after elapse of a predetermined period of time from the start of lighting.  
 
     
     
       15. An electric discharge lamp device as in  claim 14 , wherein the predetermined period of time is set depending upon a lamp turn-off time in which the lamp is maintained turned off. 
     
     
       16. An electric discharge lamp device comprising:
 a storage circuit for storing a lamp voltage signal corresponding to a lamp voltage which is detected immediately after a start of lighting a lamp;  
 a change detection circuit for detecting a change in the lamp voltage by subtracting the lamp voltage signal stored in the storage circuit immediately after the lighting from the lamp voltage signal detected currently, electric power supplied to the lamp being controlled based upon the change detected by the change detection circuit; and  
 a timer circuit for controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting,  
 wherein the timer circuit gradually decreases the electric power supplied to the lamp depending upon the elapse of time from when the change detected by the change detection circuit has exceeded a predetermined value or from when a lamp voltage has exceeded the predetermined value, whichever is earlier, so as to be shifted to the electric power that is supplied to the lamp in a stable state.  
 
     
     
       17. A method of operating an electric discharge lamp device, the method comprising:
 detecting a lamp voltage and producing a lamp voltage signal corresponding to the detected lamp voltage;  
 storing the lamp voltage signal corresponding to the lamp voltage detected immediately after a start of lighting a lamp; and  
 detecting a change in the lamp voltage by subtracting the stored lamp voltage signal from the lamp voltage signal corresponding to the lamp voltage detected after the lamp voltage is stored; and  
 controlling electric power supplied to the lamp based upon the detected change.  
 
     
     
       18. A method as in  claim 17 , wherein the stored lamp voltage signal is stored after an elapse of a predetermined period of time from the start of lighting the lamp as the lamp voltage detected immediately after the start of lighting the lamp. 
     
     
       19. A method as in  claim 18 , wherein the predetermined period of time is not longer than 6 seconds. 
     
     
       20. A method as in  claim 19 , wherein the stored lamp voltage signal is a minimum voltage value in the predetermined period of time. 
     
     
       21. A method as in  claim 17 , further comprising controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting, and gradually decreasing the electric power supplied to the lamp depending upon the elapse of time from when the detected change has exceeded a predetermined value to be shifted to the electric power that is supplied to the lamp in a stable state. 
     
     
       22. A method as in  claim 21 , wherein the electric power supplied to the lamp is gradually decreased irrespective of the change of the lamp voltage signal after elapse of a predetermined period of time from the start of lighting. 
     
     
       23. A method as in  claim 22 , wherein the predetermined period of time is set depending upon a lamp turn-off time in which the lamp is maintained turned off. 
     
     
       24. A method as in  claim 17 , further comprising:
 controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting, and gradually decreasing the electric power supplied to the lamp depending upon the elapse of time from when the detected change has exceeded a predetermined value or from when a lamp voltage has exceeded the predetermined value, whichever is earlier, so as to be shifted to the electric power that is supplied to the lamp in a stable state.  
 
     
     
       25. A method as in  claim 17 , wherein the electric discharge lamp device is a mercury-free lamp device. 
     
     
       26. A method as in  claim 25 , wherein the mercury-tree lamp device is mounted on a vehicle. 
     
     
       27. An electric discharge lamp control device for a vehicle comprising:
   present voltage detection means for detecting a present lamp voltage;        storage means for storing a lamp voltage signal indicating the lamp voltage detected immediately after a start of lighting a lamp; and        control means for controlling electric power supplied to the lamp based upon a change varying in dependence on the lamp voltage signal stored in the storage means and the lamp voltage detected by the present voltage detection means.     
     
     
       28. An electric discharge lamp control device as in  claim 27 , wherein the storage means is adapted to store the lamp voltage signal after an elapse of a predetermined period of time from the start of lighting the lamp as the lamp voltage detected immediately after the start of lighting the lamp. 
     
     
       29. An electric discharge lamp control device as in  claim 28 , wherein the predetermined period of time is not longer than  6  seconds. 
     
     
       30. An electric discharge lamp control device as in  claim 29 , wherein the lamp voltage signal stored in the storage means is a minimum voltage value in the predetermined period of time. 
     
     
       31. An electric discharge lamp control device as in  claim 27 , further comprising:
   a timer circuit for controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting,        wherein the timer circuit is adapted to gradually decrease the electric power supplied to the lamp depending upon the elapse of time from when the change exceeds a predetermined value to be shifted to the electric power that is supplied to the lamp in a stable state.     
     
     
       32. An electric discharge lamp control device as in  claim 31 , wherein the timer circuit is adapted to gradually decrease the electric power supplied to the lamp irrespective of the change of the lamp voltage signal after elapse of a predetermined period of time from the start of lighting. 
     
     
       33. An electric discharge lamp control device as in  claim 32 , wherein the predetermined period of time is set depending upon a lamp turn- off time in which the lamp is maintained turned off.   
     
     
       34. An electric discharge lamp control device as in  claim 27 , further comprising:
   a timer circuit for controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting,        wherein the timer circuit is adapted to gradually decrease the electric power supplied to the lamp depending upon the elapse of time from when the change exceeds a predetermined value or from when a lamp voltage has exceeded the predetermined value, whichever is earlier, so as to be shifted to the electric power that is supplied to the lamp in a stable state.     
     
     
       35. An electric discharge lamp control device as in  claim 27 , wherein the electric discharge control lamp device is a mercury- free lamp control device.   
     
     
       36. An electric discharge lamp control device as in  claim 27 , wherein the electric discharge lamp control device is a device for controlling a mercury- free lamp mounted on a vehicle.   
     
     
       37. An electric discharge lamp control device as in  claim 35 , wherein the mercury- free lamp control device controls a mercury - free lamp which is mounted on a vehicle.   
     
     
       38. An electric discharge lamp control device for a vehicle as in  claim 37 , wherein the storage means is adapted to store the lamp voltage signal in an initial stage of lighting. 
     
     
       39. An electric discharge lamp control device as in  claim 37 , further comprising:
   a DC power source for supplying the electric power to a lamp inverter circuit for driving the lamp with alternating current based on the electric power by the DC power source,        wherein the control means is adapted to control the electric power by controlling the DC power source supplied to the lamp inverter circuit.     
     
     
       40. An electric discharge lamp control device for a vehicle as in  claim 37 , wherein the control means is adapted to decrease the electric power supplied to the lamp in response to an increase of the change. 
     
     
       41. An electric discharge lamp control device as in  claim 37 , wherein the control means is adapted to start decreasing the electric power supplied to the lamp in response to a larger decreasing rate at a time that the change has reached a predetermined fixed value, the larger decreasing rate being larger than a decreasing rate until the change reaches the predetermined fixed value. 
     
     
       42. An electric discharge lamp control device as in  claim 40 , further comprising:
   judging means for judging whether it is a hot start or cold start when lighting the lamp is started,        wherein the control means is adapted to decrease the electric power supplied to the lamp, before the change reaches the predetermined fixed value based on the judgment as the cold start.     
     
     
       43. An electric discharge lamp control device as in  claim 42 , wherein the judging means is adapted to judge as the hot start in the case that the lamp voltage detected by the present voltage detection means becomes larger than a predetermined value, before the change reaches the predetermined fixed value. 
     
     
       44. An electric discharge lamp control device as in  claim 42 , wherein the judging means is adapted to judge as the hot start when an elapsed time from the lamp lighting becomes longer than a predetermined threshold, before the change becomes larger than the predetermined fixed value. 
     
     
       45. An electric discharge lamp control device as in  claim 44 , wherein the predetermined threshold corresponds to a length of a turn- off period before lighting.   
     
     
       46. An electric discharge lamp control device for a vehicle comprising:
   a lamp voltage detection circuit for detecting a lamp voltage and producing a lamp voltage signal;        a storage circuit for storing the lamp voltage signal produced from a lamp voltage detected immediately after each start of lighting a lamp; and        a controller for controlling electric power supplied to the lamp based upon a change varying in dependence on the lamp voltage signal stored by the storage circuit and a lamp voltage signal detected by the lamp voltage detection circuit after the lamp voltage signal is stored by the storage circuit.     
     
     
       47. An electric discharge lamp control device for a vehicle comprising:
   a storage circuit for storing a lamp voltage signal corresponding to a lamp voltage which is detected immediately after a start of lighting a lamp; and        a change detection circuit for detecting a change in the lamp voltage based on the lamp voltage signal stored in the storage circuit immediately after the lighting and the lamp voltage signal corresponding to the lamp voltage being detected currently,        wherein electric power supplied to the lamp is controlled based upon the change detected by the change detection circuit;        wherein the storage circuit stores the lamp voltage signal after an elapse of a predetermined period of time from the start of lighting the lamp as the lamp voltage detected immediately after the start of lighting the lamp, the predetermined period of time not being longer than  6  seconds.     
     
     
       48. An electric discharge lamp control device as in  claim 47 , wherein the lamp voltage signal stored in the storage circuit is a minimum voltage value in the predetermined period of time. 
     
     
       49. An electric discharge lamp control device for a vehicle comprising:
   a storage circuit for storing a lamp voltage signal corresponding to a lamp voltage which is detected immediately after a start of lighting a lamp;        a change detection circuit for detecting a change in the lamp voltage between the lamp voltage signal stored in the storage circuit immediately after the lighting and the lamp voltage signal corresponding to the lamp voltage being detected currently, electric power supplied to the lamp being controlled based upon the change detected by the change detection circuit; and        a timer circuit for controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting;        wherein the timer circuit gradually decreases the electric power supplied to the lamp depending upon the elapse of time from when the change detected by the change detection circuit exceeds a predetermined value to be shifted to the electric power that is supplied to the lamp in a stable state;        wherein the timer circuit gradually decreases the electric power supplied to the lamp irrespective of the change of the lamp voltage signal after elapse of a predetermined period of time from the start of lighting.     
     
     
       50. An electric discharge lamp control device as in  claim 49 , wherein the predetermined period of time is set depending upon a lamp turn- off time in which the lamp is maintained turned off.   
     
     
       51. An electric discharge lamp control device for a vehicle comprising:
   a storage circuit for storing a lamp voltage signal corresponding to a lamp voltage which is detected immediately after a start of lighting a lamp;        a change detection circuit for detecting a change in the lamp voltage varying with the lamp voltage signal stored in the storage circuit immediately after the lighting and the lamp voltage signal detected currently, electric power supplied to the lamp being controlled based upon the change detected by the change detection circuit; and        a timer circuit for controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting,        wherein the timer circuit gradually decreases the electric power supplied to the lamp depending upon the elapse of time from when the change detected by the change detection circuit has exceeded a predetermined value or from when a lamp voltage has exceeded the predetermined value, whichever is earlier, so as to be shifted to the electric power that is supplied to the lamp in a stable state.     
     
     
       52. A method of operating an electric discharge lamp device, the method comprising:
   detecting a lamp voltage and producing a lamp voltage signal corresponding to the detected lamp voltage;        storing the lamp voltage signal corresponding to the lamp voltage detected immediately after a start of lighting a lamp; and        controlling electric power supplied to the lamp based upon a change varying in dependence on the lamp voltage signal stored and the lamp voltage signal detected after the storing.     
     
     
       53. A method as in  claim 52 , wherein the stored lamp voltage signal is stored after an elapse of a predetermined period of time from the start of lighting the lamp as the lamp voltage detected immediately after the start of lighting the lamp. 
     
     
       54. A method as in  claim 53 , wherein the predetermined period of time is not longer than  6  seconds. 
     
     
       55. A method as in  claim 54 , wherein the stored lamp voltage signal is a minimum voltage value in the predetermined period of time. 
     
     
       56. A method as in  claim 52 , wherein the controlling controls the electric power supplied to the lamp further based upon an elapse of time after the start of lighting, and gradually decreases the electric power supplied to the lamp depending upon the elapse of time from when the change has exceeded a predetermined value to be shifted to the electric power that is supplied to the lamp in a stable state. 
     
     
       57. A method as in  claim 56 , wherein the electric power supplied to the lamp is gradually decreased irrespective of the change of the lamp voltage signal after elapse of a predetermined period of time from the start of lighting. 
     
     
       58. A method as in  claim 57 , wherein the predetermined period of time is set depending upon a lamp turn- off time in which the lamp is maintained turned off.   
     
     
       59. A method as in  claim 52 , further comprising:
   controlling the electric power supplied to the lamp depending upon an elapse of time after the start of lighting, and gradually decreasing the electric power supplied to the lamp depending upon the elapse of time from when the change has exceeded a predetermined value or from when a lamp voltage has exceeded the predetermined value, whichever is earlier, so as to be shifted to the electric power that is supplied to the lamp in a stable state.     
     
     
       60. A method as in  claim 52 , wherein the electric discharge lamp device is a mercury- free lamp device mounted on a vehicle.   
     
     
       61. A mercury- free electric discharge lamp control device for a vehicle comprising:      present voltage detection means for detecting a present lamp voltage supplied to a mercury - free electric discharge lamp;        storage means for storing a lamp voltage at a time of a start of an initial stage of lighting the lamp; and        control means for decreasing electric power supplied to the lamp in accordance with time when a change between the stored lamp voltage and the present lamp voltage reaches a first predetermined fixed value.     
     
     
       62. A mercury- free electric discharge lamp control device according to    claim 61   , wherein the stored lamp voltage represents a lamp voltage held after elapse of a predetermined period of time during the initial stage of lighting the lamp as the lamp voltage at the time of the start of the initial stage of lighting the lamp.   
     
     
       63. The mercury- free electric discharge lamp control device according to    claim 61   , wherein the stored lamp voltage represents a lowest lamp voltage held during the initial stage of lighting the lamp.   
     
     
       64. The mercury- free electric discharge lamp control device according to    claim 61   , wherein the control means is adapted to decrease the electric power supplied to the lamp when the change between the stored lamp voltage and the present lamp voltage reaches the first predetermined fixed value, if a predetermined time elapses after the change has reached the first predetermined fixed value.   
     
     
       65. The mercury- free electric discharge lamp control device according to    claim 61   , wherein the control means is adapted to decrease the electric power supplied to the lamp, if a predetermined time elapses before the change has reached the first predetermined fixed value.   
     
     
       66. The mercury- free electric discharge lamp control device according to    claim 61   , wherein the control means is adapted to decrease the electric power supplied to the lamp when the change between the stored lamp voltage and the present lamp voltage reaches a first predetermined fixed value, if the present voltage reaches a second predetermined fixed value after the change has reached the first predetermined fixed value.   
     
     
       67. The mercury- free electric discharge lamp control device according to    claim 61   , wherein the control means is adapted to decrease the electric power supplied to the lamp, if the present voltage reaches a second predetermined fixed value before the change has reached the first predetermined fixed value.   
     
     
       68. A mercury- free electric discharge lamp control device for a vehicle comprising:      judging means for judging whether a light flux of a lamp reaches a value in relation to substantially  80   %  or more of the maximum light flux; and        control means for controlling electric power supplied to the lamp in accordance with time, when the judging means affirms the value having reached in relation to substantially  80   %  or more of the maximum light flux.     
     
     
       69. The mercury- free electric discharge lamp control device according to    claim 68   , further comprising:      determination means for determining the light flux by relating a stored lamp voltage stored in an initial stage of lighting the lamp with a present lamp voltage.     
     
     
       70. The mercury- free electric discharge lamp control device according to    claim 69   , wherein the stored lamp voltage represents a lamp voltage sample - held after elapse of a predetermined period of time during the initial stage of lighting the lamp.   
     
     
       71. The mercury- free electric discharge lamp control device according to    claim 69   , wherein the stored lamp voltage represents a lowest lamp voltage sample - held during the initial stage of lighting the lamp.   
     
     
       72. A mercury- free electric discharge lamp control device for a vehicle comprising:      a control circuit for decreasing electric power supplied to the lamp in accordance with time in relation to a level of light flux of the lamp;        wherein the level of the light flux is identified by a change of the lamp voltage becoming a fixed value substantially, the change being a difference between a lamp voltage stored immediately after a start of an initial stage of lighting the lamp and a present lamp voltage.     
     
     
       73. The mercury- free electric discharge lamp control device according to    claim 72   , wherein the stored lamp voltage represents a lamp voltage sample - held after elapse of a predetermined period of time during the initial stage of lighting the lamp.   
     
     
       74. The mercury- free electric discharge lamp control device according to    claim 72   , wherein the stored lamp voltage represents a lowest lamp voltage sample - held during the initial stage of lighting the lamp.   
     
     
       75. A mercury- free electric discharge lamp control device for a vehicle comprising:      means for providing a first threshold value and a second threshold value, which is larger than the first threshold value;        control means for controlling electric power supplied to a lamp based on a change between a lamp voltage stored immediately after a start of an initial stage of lighting the lamp and a present lamp voltage, wherein        the control means is adapted to compare the first threshold value with the change so as to suppress overshoot of the light flux, and to compare the second threshold value with the change so as to suppress undershoot of the light flux, such that the electric power supplied to the lamp is controlled in accordance with a comparison result of the comparison to the first threshold value and the comparison to the second threshold value.     
     
     
       76. The mercury- free electric discharge lamp control device according to    claim 75   , wherein the stored lamp voltage represents a lamp voltage sample - held after elapse of a predetermined period of time during the initial stage of lighting the lamp as the lamp voltage stored immediately after the start of the initial stage of lighting the lamp.   
     
     
       77. The mercury- free electric discharge lamp control device according to    claim 75   , wherein the stored lamp voltage represents a lowest lamp voltage sample - held during the initial stage of lighting the lamp.   
     
     
       78. The mercury- free electric discharge lamp control device according to    claim 75   ,      wherein, if the comparison result indicates that the change is smaller than the first threshold value,        the control means supplies a first constant power to the lamp,        if the comparison result indicates that the change is greater than the first threshold value but smaller than the second threshold value,        the control means decreases the power supplied to the lamp in accordance with the change, and        if the comparison result indicates that the change is greater than the second threshold value,        the control means supplies a constant second power smaller than the first power to the lamp.     
     
     
       79. A mercury- free electric discharge lamp control device for a vehicle comprising:      means for providing a threshold value;        control means for controlling electric power supplied to a lamp based on a change between a lamp voltage stored immediately after a start of an initial stage of lighting the lamp and a present lamp voltage, wherein        the control means is adapted to compare the threshold value with the change so as to suppress undershoot of light flux of the lamp, such that the electric power supplied to the lamp is controlled in accordance with the comparison result.     
     
     
       80. The mercury- free electric discharge lamp control device according to    claim 79   , wherein the stored lamp voltage represents a lamp voltage sample - held after elapse of a predetermined period of time during the initial stage of lighting the lamp as the lamp voltage stored immediately after the start of the initial stage of the lighting the lamp.   
     
     
       81. The mercury- free electric discharge lamp control device according to    claim 79   , wherein the stored lamp voltage represents a lowest lamp voltage sample - held during the initial stage of lighting the lamp.   
     
     
       82. The mercury- free electric discharge lamp control device according to    claim 79   ,      if the comparison result indicates that the change is smaller than the threshold value,        the control means decreases the power supplied to the lamp in accordance with the change, and        if the comparison result indicates that the change is greater than the threshold value,        the control means supplies a constant power to the lamp.     
     
     
       83. An electric discharge lamp control device as in  claim 46 , wherein the electric discharge control lamp device is a mercury- free lamp control device.   
     
     
       84. An electric discharge lamp control device as in  claim 46 , wherein the electric discharge lamp control device is a device for controlling a mercury- free lamp mounted on a vehicle.   
     
     
       85. An electric discharge lamp control device as in  claim 83 , wherein the mercury- free lamp control device controls a mercury - free lamp which is mounted on a vehicle.   
     
     
       86. An electric discharge lamp control device as in  claim 47 , wherein the electric discharge control lamp device is a mercury- free lamp control device.   
     
     
       87. An electric discharge lamp control device as in  claim 47 , wherein the electric discharge lamp control device is a device for controlling a mercury- free lamp mounted on a vehicle.   
     
     
       88. An electric discharge lamp control device as in  claim 86 , wherein the mercury- free lamp control device controls a mercury - free lamp which is mounted on a vehicle.   
     
     
       89. An electric discharge lamp control device as in  claim 49 , wherein the electric discharge control lamp device is a mercury- free lamp control device.   
     
     
       90. An electric discharge lamp control device as in  claim 49 , wherein the electric discharge lamp control device is a device for controlling a mercury- free lamp mounted on a vehicle.   
     
     
       91. An electric discharge lamp control device as in  claim 89 , wherein the mercury- free lamp control device controls a mercury - free lamp which is mounted on a vehicle.   
     
     
       92. An electric discharge lamp control device as in  claim 51 , wherein the electric discharge control lamp device is a mercury- free lamp control device.   
     
     
       93. An electric discharge lamp control device as in  claim 51 , wherein the electric discharge lamp control device is a device for controlling a mercury- free lamp mounted on a vehicle.   
     
     
       94. An electric discharge lamp control device as in  claim 92 , wherein the mercury- free lamp control device controls a mercury - free lamp which is mounted on a vehicle.   
     
     
       95. An electronic discharge lamp device as in  claim 1 , wherein the lamp voltage signal stored in the storage means as the lamp voltage detected immediately after a start of lighting a lamp is a minimum value of the lamp voltage detected by the lamp voltage detection means in a predetermined period of time from the start of lighting a lamp. 
     
     
       96. An electronic discharge lamp device as in  claim 27 , wherein the control means is configured to continue to use the lamp voltage signal stored in the storage means in determining the change during control of the electric power. 
     
     
       97. An electric discharge lamp control device as in  claim 96 , wherein the storage means is adapted to store the lamp voltage signal after an elapse of a predetermined period of time from the start of lighting the lamp as the lamp voltage detected immediately after the start of lighting the lamp. 
     
     
       98. An electric discharge lamp control device as in  claim 97 , wherein the predetermined period of time is not longer than  6  seconds. 
     
     
       99. An electric discharge lamp control device for a vehicle comprising:
   present voltage detection means for detecting a present lamp voltage;        storage means for storing a lamp voltage signal indicating the lamp voltage detected immediately after a start of lighting a lamp; and        control means for controlling electric power supplied to the lamp based upon a change varying in dependence on the lamp voltage signal stored in the storage means and the lamp voltage detected by the present voltage detection means;        wherein the lamp voltage signal stored in the storage means is substantially minimum voltage value in a predetermined period of time from the start of lighting the lamp.     
     
     
       100. A method of operating an electric discharge lamp device, the method comprising:
   detecting a lamp voltage and producing a lamp voltage signal corresponding to the detected lamp voltage;        storing the lamp voltage signal corresponding to the lamp voltage detected immediately after a start of lighting a lamp; and        controlling electric power supplied to the lamp based upon a change varying in dependence on the lamp voltage signal stored and the lamp voltage signal detected after the storing;        wherein the stored lamp voltage signal is substantially a minimum voltage value in a predetermined period of time from the start of lighting the lamp.     
     
     
       101. A mercury- free electric discharge lamp control device according to    claim 72   , wherein the change is continuously calculated as the difference of the present lamp voltage from the stored lamp voltage.   
     
     
       102. A mercury- free electric discharge lamp control device for a vehicle comprising:      a control circuit for controlling a decreased amount of electric power supplied to a mercury - free lamp in accordance with time in relation to a level of light flux of the lamp,        wherein the level of the light flux is identified by a change of the lamp voltage becoming a fixed value substantially, the change being a difference between an initial lamp voltage of the mercury - free lamp detected and stored after a start of an initial stage of lighting the lamp and a present lamp voltage of the mercury - free lamp detected after detection of the initial lamp voltage.     
     
     
       103. A mercury- free electric discharge lamp control device according to    claim 102   , wherein the initial lamp voltage corresponds to a lowest lamp voltage sample - held during the initial stage of lighting the mercury - free lamp.   
     
     
       104. A mercury- free electric discharge lamp control device for a vehicle comprising:      means for providing a first threshold value and a second threshold value, which is larger than the first threshold value;        control means for controlling electric power supplied to a lamp based on a change between a lamp voltage stored at time of a start of an initial stage of lighting the lamp and a present lamp voltage, wherein        the control means is adapted to compare the first threshold value with the change so as to suppress overshoot of the light flux, and to compare the second threshold value with the change so as to suppress undershoot of the light flux, such that the electric power supplied to the lamp is controlled in accordance with a comparison result of the comparison to the first threshold value and the comparison to the second threshold value.     
     
     
       105. A mercury- free electric discharge lamp control device according to    claim 79   , wherein the change is continuously calculated as the difference of the present lamp voltage from the stored lamp voltage.   
     
     
       106. An electric discharge lamp control device for a vehicle comprising:
   a present voltage detection part configured to detect a present voltage of a mercury - free lamp;        a storage part configured to store an initial voltage of the mercury - free lamp in an initial stage of lighting the mercury - free lamp; and        a control part configured to control electric power supplied to the mercury - free lamp based on a change of the present voltage relative to the initial voltage stored in the storage part.     
     
     
       107. An electric discharge lamp control device according to  claim 106 , wherein the change is increased as the present voltage increases after the initial stage of lighting. 
     
     
       108. An electric discharge lamp control device according to  claim 106 , wherein the storage part is configured to store, as the initial voltage, a substantially minimum voltage of the present voltage detected in the initial stage of lighting the mercury- free lamp by the present voltage detection part.   
     
     
       109. An electric discharge lamp control device according to  claim 106 , wherein the control part is configured to perform electric power decrease control for the mercury- free lamp based on the change.   
     
     
       110. An electric discharge lamp control device for a vehicle comprising:
   a present voltage detection part configured to detect a present voltage of a mercury - free lamp;        a storage part configured to store an initial voltage of the mercury - free lamp at an initial stage of lighting the mercury - free lamp;        a change calculating part configured to calculate a change of the present voltage relative to the initial voltage stored in the storage part; and        a control part configured to control electric power supplied to the mercury - free lamp in accordance with time at which the change reaches a predetermined value.     
     
     
       111. An electric discharge lamp control device according to  claim 110 , wherein the change is increased as the present voltage increases after the initial stage of lighting. 
     
     
       112. An electric discharge lamp control device according to  claim 110 , wherein the storage part is configured to store, as the initial voltage, a substantially minimum voltage of the present voltage detected in the initial stage of lighting the mercury- free lamp by the present voltage detection part.   
     
     
       113. An electric discharge lamp control device according to  claim 110 , wherein the control part is configured to perform electric power decrease control for the mercury- free lamp based on the change.   
     
     
       114. An electric discharge lamp control device according to  claim 110 , wherein:
   the control part is configured to control the electric power to suppress overshoot of the electric power based on the predetermined value; and        the control part is further configured to control the electric power to suppress undershoot of the electric power based on another predetermined value different from the predetermined value provided for overshoot suppression.     
     
     
       115. An electric discharge lamp control device for a vehicle comprising:
   a present voltage detection part configured to detect a present voltage of a mercury - free lamp;        a storage part configured to store a substantially minimum voltage value detected by the present voltage detection part in an initial stage of lighting the mercury - free lamp; and        a control part configured to control electric power supplied to the mercury - free lamp based on a change of the present voltage relative to the substantially minimum voltage value stored in the storage part.     
     
     
       116. An electric discharge lamp control device according to  claim 115 , wherein the change is increased as the present voltage increases after the initial stage of lighting. 
     
     
       117. An electric discharge lamp control device according to  claim 115 , wherein the control part is configured to perform electric power decrease control for the mercury- free lamp based on the change.   
     
     
       118. An electric discharge lamp control device for a vehicle comprising:
   a present voltage detection part configured to detect a present voltage of a mercury - free lamp;        a storage part configured to store a substantially minimum voltage value detected by the present voltage detection part in an initial stage of lighting the mercury - free lamp; and        a control part configured to control electric power supplied to the mercury - free lamp based on the substantially minimum voltage value and the present voltage value thereby to suppress overshoot of light flux of the mercury - free lamp.