In this type of lamp the filament is made of carbon. The melting point of carbon is 3500℃ but its working temperature should not exceed 1800℃ because at high temperature it starts disintegrating and blackens the inside of the bulb. Its temperature Co-efficient is negative. So the resistance decreases at high temperature and taken more CURRENT resulting high power consumption. The efficiency of this lamp is low of about 4 lumens per watt. It gives yellowish LIGHT. It is GENERALLY used for heating purposes and to create a voltage drop for example in battery charging but not for lighting purpose. The approximate life of this lamp is about 800-900 HOURS.

In this type of lamp the filament is made of carbon. The melting point of carbon is 3500℃ but its working temperature should not exceed 1800℃ because at high temperature it starts disintegrating and blackens the inside of the bulb. Its temperature Co-efficient is negative. So the resistance decreases at high temperature and taken more current resulting high power consumption. The efficiency of this lamp is low of about 4 lumens per watt. It gives yellowish light. It is generally used for heating purposes and to create a voltage drop for example in battery charging but not for lighting purpose. The approximate life of this lamp is about 800-900 hours.