Patent ID: 9623791
Date: 2017-04-18
CPC Classifications: B60Q,F21S,F21Y,H05B

Claim:
1. A lighting device comprising: a lighting circuit configured to supply a current to a light source device; and a control circuit configured to perform dimming control of the lighting circuit according to a desired dimming level to thereby dim the light source device, the dimming control including amplitude control and pulse width modulation control, the amplitude control being control of adjusting a current value of the current to a desired current value, the pulse width modulation control being control of adjusting a duty cycle to a desired duty cycle, the duty cycle being defined as a ratio of an on-period to a cycle being a sum of the on-period and an off-period, the on-period being a period in which the current flows through the light source device, the off-period being a period in which the current does not flow through the light source device, a total dimming range of the light source device including multiple different dimming subranges which are different ranges of dimming levels and associated with different predetermined values each of which is defined as the duty cycle which allows luminance of the light source device to be equal to preliminarily determined upper limit luminance of an associated one of the multiple different dimming subranges under a condition where the current value of the current is a maximum value, and, the control circuit being configured to, in the dimming control, set the desired current value to a value corresponding to the desired dimming level, and further set the desired duty cycle to one of the different predetermined values associated with one of the multiple dimming subranges which contains the desired dimming level.