A light source apparatus (8) includes a rear plate (80), a front plate formed with an anode layer (82), and a cathode (81) interposed therebetween. The cathode includes a plurality of electrically conductive carriers (812) and a plurality of field emitters (816) formed thereon. The field emitters are uniformly distributed on anode-facing surfaces of the conductive carriers. Preferably, the field emitters extend radially outwardly from the corresponding conductive carriers. The conductive carriers are parallel with each other, and are located substantially on a common plane. Each of the conductive carriers can be connected with a pulling device arranged at least one end thereof, and an example of the pulling device is a spring. The conductive carriers may be cylindrical, prism-shaped or polyhedral.