24V is just fine for a string of up to 6 LEDs. Your comment leads me to think you haven't designed many switching regulators. You can drive up to six LEDs from

24V is just fine for a string of up to 6 LEDs. Your comment leads me to think you haven't designed many switching regulators. You can drive up to six LEDs from 24V at 92% efficiency with 6 components (I have a device I've designed in front of me that proves it): one IC, an inductor, a resistor, a diode and two tiny capacitors.