Drives LEDs with a regulated output voltage or current (up to 120mA) from an unregulated input supply (2.7V to 5.3V). These are complete DC-DC converters requiring only four small ceramic capacitors and no inductors. 200mV Current-Sense Threshold Reduces Power Loss.
The MAX1561 and MAX1599 include an internal, high-voltage, low-RDS(ON) N-channel MOSFET switch for high efficiency and maximum battery life. A single DualMode input provides a simple means of brightness adjustment and on/off control. MAX1561 - 26V Step-Up Converters - Maxim IC
"High-Efficiency, 26V Step-Up Converters for Two to Six White LEDs"
Fast 1MHz (500kHz for the MAX1599) current-mode, pulse-width modulated (PWM) operation allows for small input and output capacitors and a small inductor while minimizing ripple on the input supply/battery. Programmable soft-start eliminates inrush current during startup.
Some Features -
Accurate Current Regulation for Uniform Illumination
High Efficiency Up to 87%
2.6V to 5.5V Input Range
0.3µA Shutdown Current
26V (max) Output with Overvoltage Protection
Up to 900mW Output Power with Internal 30V MOSFET Switch
Here you can understand how to drive white LED' s for flashlight or Internal lamp. I have tried substituting for tubelights and bulbs. These LED's are amazing. The amount of light at even 100mW is phenomenal. The future is indeed LED Lights. But more Amber component is required in LED to give the warm feeling of an Edison Lamp.