Most efficient way to drive an LED from 9v source?
A voltage divider will waste power, as it will have current flowing through the lower resistor, as well as through the LED.

The 430 Ohm resistor will allow about 12 mA through the LED.  A higher value series resistor will reduce the LED current, and decrease the brightness.  You may find that a 1K or higher resistor will still allow the LED to produce sufficient light.