An LED light bulb is a solid state light that uses light emitting diodes as their source of light. These LEDs can be a conventional semiconductor light emitting diodes to organic LEDs (OLED), or (PLEDs) which are polymer light emitting diodes, although these are not yet commercially available. Because the light output of these diodes is small, compared to normal bulbs, multiple diodes are often used together. The developments in recent years have improved greatly, the power of these LEDs namely the lumen output has meant that standard bulbs are being replaced with these new type lamps. For example, one LED chip used in some forms of commercial lighting can emit 7527 lumens, while still only using 100 watts. They can also be used in other types of lamps. These diodes use a direct current so they must incorporate transforming circuitry to operate on an alternating current. LEDs are damaged by high temperatures and so they must also use a heat management system to cool them, usually in the form of heatsinks or cooling fans. They are very reliable and give a good long service; however their initial cost is higher than the normal fluorescent or incandescent bulbs.