Carbon arc lamps are one among the many forms of arc lamps, which is quite popular. So, these lamps have electrodes of hard carbon which is placed at one end and connected to a d.c. Source. So, when the current flows through them, the ends of carbon rods become incandescent due to high resistance. However, if this formation is pulled slightly apart about 2-3 cm distance, then an arc will be formed. It will be between two carbon rods which produce white light. Moreover, the luminous efficiency of this lamp is about 9 lumens per watt. And in cinema projectors and searchlights these lamps are used.