You’ve noticed them popping up in flash lights, Christmas lights, car lights and even the occasional light bulb but what are LED lights and why are the so expensive?
LED is short for Light Emitting Diode, and has been around for decades. That red 
computer light on your PC or the lights on the knobs of your stereo are probably one. The were originally made in red, green and yellow. As more manufacturers used them cost began to come down. So they started appearing in more electronics and more colors.
Spring forward to the last decade where energy has become a focal point of many governments and reducing dependence on foreign oil and you have laws that are being made to promote energy savings. An example of this is the the end to most incandescent light bulb sales here in the US in 2014.
LED Light Bulb Advantages
The big advantage of LED Lighting is the dramatic reduction in energy consumption. LEDs on average consume 10%of the energy than standard light bulbs. That is a dramatic 
savings in energy consumption and $$$. The current issue with LEDs are the cost to install them. You have to think long term to justify buying a $40-$150 light bulb. I found a nifty LED cost calculator here that gives tells you how much you save switching. Plugging in a standard home owners light bulb I would save on average $12 a year per bulb in energy cost. That would mean it would take about 3.5 years to recoup my cost on these bulbs. Not bad, but I think manufacturers can do better. When CFLs hit the market a decade ago they cost $10 a piece or more, now you can get a 3 pack for $7. Clearly economies of scale have to kick in before homeowners switch. But I expect that to happen quickly over the next few years as incandescent are no longer available and LEDs quickly become mainstream.
For now I would expect manufacturing, offices and other commercial spaces that run lights non stop to make the switch first. I would recommend changing any lights in your home that are constantly on be switched over now, such as a porch light.