Do you always need a buckpuck for high powered LEDs? Answered

For a high powered LED (or series of LEDs) you're going to want a constant-current regulator of some kind.  The reason this regulator is needed is because without a current regulator, the LED will tend to draw too much current, and thus too much power (the product of voltage and current), and thus burn itself out.

The quote below is from here:
http://en.wikipedia.org/wiki/Light-emitting_diode#Power_sources
The parts in bold are words I think deserve emphasis.

The current/voltage characteristic of an LED is similar to other diodes, in that the current is dependent exponentially on the voltage (see Shockley diode equation). This means that a small change in voltage can lead to a large change in current. If the maximum voltage rating is exceeded by a small amount the current rating may be exceeded by a large amount, potentially damaging or destroying the LED.The typical solution is therefore to use constant current power supplies, or driving the LED at a voltage much below the maximum rating. Since most household power sources (batteries, mains) are not constant current sources, most LED fixtures must include a power converter.

Its never a great idea to rely on that. Steve