The photosensitive Belousov-Zhabotinsky (BZ) reaction was investigated at an asymmetrically illuminated gap, which was drawn using computer software and then projected on a filter paper soaked with BZ solution using a liquid-crystal projector. The probability of the chemical wave passing through the gap with asymmetric illumination was different from that through its mirror image. The location at which the wave disappeared and the time delay of the chemical wave passing through the gap changed depending on the velocity of chemical wave propagation. The experimental results were qualitatively reproduced by a theoretical calculation based on the three-variable Oregonator model that included photosensitivity. These results suggest that the photosensitive BZ reaction may be useful for studying spatiotemporal development that depends on the geometry of excitable fields.