As shown in FIG. 7D, a length of the first portion 100p1 of the LED filament 100 in the first quadrant in the side view is substantially equal to a length of the second portion 100p2 of the LED filament 100 in the second quadrant in the side view. In the embodiment, the length is defined along an elongated direction of the LED filament 100 in a plane view (e.g., a side view, a front view, or a top view). For example, the first portion 100p1 elongates in the first quadrant in the side view shown in FIG. 7D to form a reversed “V” shape with two ends respectively contacting the X-axis and the Y-axis, and the length of the first portion 100p1 is defined along the reversed “V” shape between the X-axis and the Y-axis.
In addition, a length of the third portion 100p3 of the LED filament 100 in the third quadrant in the side view is substantially equal to a length of fourth portion 100p4 of the LED filament 100 in the fourth quadrant in the side view. Since the third portion 100p3 and the fourth portion 100p4 are symmetric with respect to the Y-axis with a tolerance in structure, there may be a slightly difference between the length of the third portion 100p3 and the length of fourth portion 100p4. The difference may be 20%-50% or less.
