Hi,
Usually it is hard to match the voltage to the LED(s) for good efficiency. If you can that's great, but you need to analyze the circuit very carefully. If you cant then you need a switcher. Not just any switcher however, you want a switcher that uses a controller IC and external MOSFET. This is so that you can choose the MOSFET to be overrated for the application (very low Rds). Most ready made switcher packages have a switch transistor that ends up being a tradeoff in cost for efficiency. Using an external MOSFET eliminates this contradiction and gets the efficiency up near the max theoretical. Of course low loss inductor too, low drop Schottky or go with a dual MOSFET synchronous design. This also gives you a lot more flexibility with the choice of LED voltage ratings and power supply tolerance.