Based upon symmetry characteristic of LED filament 100, the structures of the two symmetric portions of the LED filament 100 in the top view (the first portion 100p1 and the second portion 100p2 or the third portion 100p3 and the fourth portion 100p4) may be exactly symmetric or be symmetric with a tolerance in structure. The tolerance (or a permissible error) between the structures of the two symmetric portions of the LED filament 100 in the top view may be 20%-50% or less.
For example, as shown in FIG. 7E, a designated point (x1, y1) on the first portion 100p1 of the LED filament 100 in the first quadrant is defined as a first position, and a symmetric point (x2, y2) on the second portion 100p2 of the LED filament 100 in the second quadrant is defined as a second position. The second position of the symmetric point (x2, y2) is symmetric to the first position of the designated point (x1, y1) with respect to the Y-axis. The first position and the second position may be exactly symmetric or be symmetric with 20%-50% difference. In the embodiment, the first portion 100p1 and the second portion 100p2 are exactly symmetric in structure. In other words, x2 of the symmetric point (x2, y2) is equal to negative x1 of the designated point (x1, y1), and y2 of the symmetric point (x2, y2) is equal to y1 of the designated point (x1, y1).
