LED bulb is a resistive bulb that uses LEDs as a light source. Because the light output of LEDs is small compared to incandescent lamps, LEDs are used in several simultaneously. LED bulbs can be used instead of incandescent bulbs. Most LED bulbs must also include the external circuits to be able to operate with standard AC power. Compared with incandescent lamps and compact fluorescent lamps offer greater durability and efficiency, but installation costs are higher. LED bulbs designed to replace conventional light bulbs are manufactured in standard sizes, with Edison thread and other threads. They are made to low voltage (eg 12 V) and the standard voltage AC (120 or 240 V).