I found this article on designing lights for cars out of LED’s to be interesting. As you may know, LED’s are far more durable, last longer and take less energy than incandescent lamps. The problem is in the past they have not been bright enough.

No doubt you have seen an increase in the number of brake and turn signal light on the street today made from LEDs. You can normally recognize them by the brake light being a large number of small dots instead of one large light source. These are frequently used on the trailers of shipping trucks, but you can also find them on passenger cars and trucks.

As technology develops they will become more common also in the headlights. This article from Photonics.com gives you an interesting overview on what it takes to design a LED based headlights.
LED Headlights