Light emitting diodes LED light bulbs have become require in recent years.but do they make financial sense suppose a typical 60-watt incandescent light bulb cost $ 46 and last a 1000 hour. A 15-watt .Led which provides the same light cost 3.45 and lasts for 12000 hours A kilowatt hour is 1000 watt for 1 hour suppose you have a residence with a lot of candescent bulb that are used an average 500 hours a year.the average will be about half way through its life so it will have 500 hour remaining and you can't tell which bulbs are older or newer if you require a 11 percent at what cost per kilowatt hour make sense to replace your incandescent light bulb.