The evaluation board can drive one or multiple LEDs on the output, limited by the minimum input voltage that you have. Since this is a buck regulator, the output voltage cannot exceed the input voltage. If you have only 6 volts on the input, you can only reliably drive one LED on the output. However, if you have 24 volts on the input, you can drive multiple LEDs up to the point of about 22 volts on the output. The board has been designed to support the maximum current from an AC input and the components have been sized for that application. The application note that describes the board includes the bill of materials for different configurations.