OPTICAL AXIS ALIGNING METHOD FOR HEADLIGHT

PURPOSE:To enable accurately aligning the optical axis of a headlight on the basis of the actual position of a light source as a reference even when the position of the light source of the headlight is shifted. CONSTITUTION:A grating body provided with a plurality of longitudinally-long grating holes arranged in the shape of a matrix is disposed in front of a headlight and the irradiation area and illuminance of a light transmitted through each grating hole in each irradiation region corresponding to each grating hole are measured. The irradiation areas of the irradiation regions (X1, Y2) and (X5, Y2) corresponding to the grating holes being opposed right to virtual light sources on the opposite right and left sides on a reflector of the headlight and of the irradiation regions between them are large and the center (X3, Y2) of distribution of the regions of which the area is large is the position of a real light source. When the direction of an optical axis is regular, an illuminance distribution being symmetric longitudinally and laterally with respect to the regions being present in a prescribed positional relationship with the position of the light source as shown in Fig. (a) (coinciding with the position of the light source in the Figure) as the center, is obtained. By adjusting the direction of the headlight so that this illuminance distribution be obtained, accurate adjustment of the optical axis can be executed.