There are currently two ways to make white light with LEDs
Multiple wavelengths of different LEDs are mixed to produce the desired color light. This allows the light to be tuned into any color, including white.
The method is referred to as RGB, and is widely used in advertising and color displays.
The second method uses a blue LED. A special phosphor coating on the LED chip turns part of the blue light into other colors, the resulting light mix is white.
This is the common method used in ¡°white LEDs¡±.
The efficiency depends heavily on the coating method and materials.