As shown in FIG. 1K, in the present embodiment, the thickness of the conductor 430a is also significantly larger than the thickness of the LED chip 442. Besides, compared with the thickness of the LED chip 442, the thickness of the conductor 430a is closer to the thickness of the top layer 420a corresponding to the conductive section 430. In the width direction of the LED filament, the top layer 420a has a width W1, and the LED chip 442 has a width W2, and the width W2 of the LED chip 442 is close to the width W1 of the top layer 420a, wherein the width direction is perpendicular to both the axial direction and the aforementioned thickness direction. That is, the top layer 420a is slightly larger than the LED chip 442 in the width direction and slightly larger than the conductor 430a in the thickness direction. In other embodiments, the ratio of the width W1 of the top layer 420a to the width W2 of the LED chip 442 is around 2 to 5, i.e., W1:W2=2?5:1. In the present embodiment, the base layer 420b has the same width W1 as the top layer 420a, but is not limited thereto. In addition, as shown in FIG. 1K, in the present embodiment, the conductive section 430 further includes a wavy concave structure 432a disposed on one side surface of the conductive section 430. In the present embodiment, the wavy concave structure 432a is recessed by the upper side surface of the top layer 420a of the conductive section 430. The plurality of wavy concave structures 432a are spaced apart in the axial direction and are parallel to each other to present a continuous wave shape. In some embodiments, the plurality of wavy concave structures 432a are continuously closely aligned along the axial direction. In some embodiments, the wavy concave structure 432a may also be disposed around the entire circumferential surface of the conductive section 430 centering on the axial direction of the LED filament. In some embodiments, the wavy concave structure 432a may also be replaced by a wavy convex structure. In some embodiments, the wavy concave structure and the wavy convex structure may be staggered together to form a wavy concave-convex structure.
