Headlamp device and luminance control method therefor

1. A headlamp device for a vehicle that has LEDs as light sources, comprising:

a situation detection portion detecting that a situation is a headlamp lighting situation in which headlamps should be on;

a headlamps control portion turning on the headlamps when the situation detection means detects that the situation is the headlamp lighting situation;

a luminance reduction portion reducing luminance of the headlamps by a prescribed amount;

an image acquiring portion that acquires image data on an area illuminated by the headlamps; and

a dimming control portion that

observes a rate of decrease in brightness of the image data on the area illuminated by the headlamps when the luminance of the headlamps is reduced by the prescribed amount by the luminance reduction portion,

compares the rate of decrease in brightness with a threshold value,

reduces the luminance of the headlamps to a prescribed value that is greater than zero based on a determination that the rate of decrease in brightness is smaller than the threshold value, and

maintains the luminance of the headlamps based on a determination that the rate of decrease in brightness is equal to or larger than the threshold value.

2. The headlamp device according to claim 1 , further comprising:

a camera as the image acquiring portion, the camera having an optical axis, the optical axis being ahead of the vehicle, the dimming control determining whether a rate of decrease in illuminance of the area illuminated by the headlamps is smaller than a threshold value by comparing pixel value information in image data acquired by the camera before the luminance of the headlamps is reduced by the prescribed amount by the luminance reduction portion and pixel value information in image data acquired by the camera after the luminance of the headlamps is reduced by the prescribed amount.

3. The headlamp device according to claim 2 , wherein

the dimming control portion monitors the pixel value information acquired when the luminance of the headlamps is gradually reduced by the luminance reduction portion, and the dimming control portion determines the luminance at a time when the pixel value information is changed by a prescribed percentage from the pixel value information before the luminance is reduced as the luminance of the headlamps.

4. The headlamp device according to claim 2 , wherein

the dimming control portion determines whether the rate of decrease in the illuminance of the area illuminated by the headlamps is smaller than the threshold value based on the pixel value information in a predetermined area in the image data, the predetermined area being more likely to be affected by the illuminance of the area illuminated by the headlamps than by a change of the surrounding scenery.

5. The headlamp device according to claim 1 , wherein the dimming control portion reduces the luminance of the headlamps by reducing the duty of a PWM signal, the PWM signal driving a plurality of LEDs.

6. The headlamp device according to claim 1 , wherein the dimming control portion reduces the luminance of the headlamps by turning off some of the plurality of LEDs.

7. The headlamp device according to claim 1 , further comprising a situation detection portion, wherein the situation detection portion detects a situation in which the vehicle turns left, as the headlamp lighting situation and the dimming control portion turns off only the headlamp on a right side.

8. The headlamp device according to claim 1 , further comprising a situation detection portion, wherein

the situation detection portion detects a situation in which the vehicle is being driven on a highway with the headlamps forming a driving beam distribution, as the headlamp lighting situation, and the dimming control portion reduces the luminance of the headlamps forming a dipped beam distribution.

9. The headlamp device according to claim 1 , further comprising a situation detection portion, wherein

the situation detection portion detects a situation in which the vehicle is being driven in a fog with fog lamps on, as the headlamp lighting situation, and the dimming control portion reduces the luminance of the headlamps.

10. The headlamp device according to claim 9 , further comprising a situation detection portion, wherein

the situation detection portion detects that the vehicle is being driven in a fog from the fact that a calculation value obtained by performing a filtering process on image data on the outside of the vehicle is equal to or greater than a threshold value, the image data being acquired by the camera, the fact that a degree of coincidence as compared to image data of a foggy scene is equal to or greater than a threshold value, the image data being preliminarily provided, or the fact that weather information acquired from outside indicates that it is foggy in the area where the vehicle is being driven.

11. A luminance control method for a headlamp device for a vehicle having LEDs as light sources, comprising:

detecting that a situation is a headlamp lighting situation in which the headlamps should be on by a situation detection portion;

turning on the headlamps when the headlamp lighting situation has been detected by a headlamp control portion;

reducing the luminance of the headlamps to a prescribed amount by a luminance reduction portion,

acquiring image data on an area illuminated by the headlamps by an image acquiring portion,

observing a rate of decrease in brightness of the image data on the area illuminated by the headlamps when the luminance of the headlamps is reduced by the prescribed amount by the luminance reduction portion,

comparing the rate of decrease in brightness with a threshold value,

reducing the luminance of the headlamps to a prescribed value that is greater than zero based on a determination that the rate of decrease in brightness is smaller than the threshold value, and

maintaining the luminance of the headlamps based on a determination that the rate of decrease in brightness is equal to or larger than the threshold value.