Conventional light bulbs use a filament, something to run current through that will heat up and produce light. These are very inefficient however, as more energy is put towards producing heat than light. This is why the idea for CFL light bulbs came about, which use a current running through gas to produce it's light. This method is more efficient, but still isn't perfect. This is where LED's come in, as they are small, very efficient, and require little power to produce a good amount of light. The reason why all lights haven't been replaced with LED lights is because of their cost, which while it's ever decreasing is still more than that of regular filament bulbs. This cost discrepancy is made more dramatic by the fact that LED's don't produce as much light per dollar spent, so for bright bulbs such as flood lights, it gets very expensive. In order to make a bright bulb, a large amount of LEDs are required, and this effect increases the brighter the bulb gets. This is exaggerated by the fact that if companies wanted to replace all of their bulbs at once, it would be expensive to install all of them, since many large buildings use a large amount of lights. I have an LED bulb in my room, and it is noticeably not as bright as a conventional bulb, but it will last a lot longer than any filament based bulb. Also, due to the fact that LED bulbs use circuitry, it isn't complicated to implement other things into the bulb. My bulb has a bluetooth speaker in it, which works very well considering it's inside of a light bulb. I think that in the future when LED technology becomes cheaper and better at producing light, all light bulbs will eventually become LED, unless they are specifically another type for one reason or another.