Transform 8~13V to 12V
DO NOT USE A VOLTAGE REGULATOR

You should never voltage regulate a LED. As an LED is a constant voltage device, voltage regulation is meaningless. The Power to Voltage graph (PV graph) is non-linear (or even polynomial) and very sensitive. A tiny over-voltage would produce a huge increase in power (destroying your LED).

EDIT: 

As Temlib says. Another reason that you should never drive an LED with a constant voltage source is that LEDs are made of semiconductors. Semiconductors when heated will reduce in resistance.

Given that 



As the Resistance decreases, the power (Ohmic heating) output increases, this leads to further reduction in resistance, which leads to more power ....

This process is called Thermal Runaway, and is a very common cause of LED failure.

Use a Constant Current Source

The correct way to drive an LED is to use a CURRENT regulator, as the the Power to Current relationship is near linear, and you can much more accurately control the power being delivered to your LED (and prevent it from releasing the magic smoke).