| 摘要 |
PURPOSE:To improve the brightness detection accuracy by detecting the brightness of disturbing light when a light emitting element is turned off and finding the difference in brightness between the brightness when a light emitting element is turned on and the brightness of the disturbing light. CONSTITUTION:The fluorescent lamp 2 is turned on/off with the lamp driving oscillation signal of an oscillation circuit 4, and a light receiving element 5 detects the light of the fluorescent lamp 2 and the disturbing light when the fluorescent lamp 2 is turned on and only the disturbing light when off. An arithmetic circuit 8 inputs the 1st output value of the light receiving element 5 when the fluorescent lamp 2 is on through a 1st switch 6 which turns on when the fluorescent lamp 2 is on and the 2nd output value of the light receiving element 5 when the fluorescent lamp 2 is off through a 2nd switch 7 which turns on when the fluorescent lamp is off, and calculates the difference between the 1st and 2nd output values to find the brightness of the fluorescent lamp 2. Therefore, the brightness of the fluorescent lamp 2 can be detected with high accuracy without being affected by the disturbing light. |
