(a) Luminance–voltage characteristics of the stretchable ACEL fiber at different bending states (1 kHz AC). The inset photographs are the stretchable ACEL fiber at different bending states. (b) Dependence of luminance on viewing angle of a stretchable ACEL fiber at 20% strain (1 kHz AC, 400 Vp). Inset shows the stretchable ACEL fiber at 20% strain. (c) Stability test of the stretchable ACEL fiber when mechanically cycled to 50% strain (1 kHz AC, 300 Vp). L0 and L correspond to luminance measured at the first cycle and the current cycle, respectively. The inset SEM image is the cross-section of the stretchable ACEL fiber after 10,000 stretching-releasing cycles. (d) The luminance statistics at 20% strain (1 kHz AC, 400 Vp) of eleven as-fabricated ACEL fibers.