We report a new turning film structure for widening the viewing angle of a vertical-field-switching blue-phase liquid crystal display, which employs a directional backlight. The turning film consists of periodic prismatic structures: each period has three prisms with different base angles so that the output light can be spread to a larger angle. Simulation results show that a full width at half-maximum of ±80° in the horizontal direction and ±45° in the vertical direction can be achieved.