Not only can one select a target current to put through an LED, but by providing a target voltage, the system will automatically calculate the necessary series resistor.

Passing an electric current through an LED causes it to emit light. When it comes to powering an LED, the simplest circuit that can be used is a voltage source with a resistor and an LED in series.

Resistors (Ω) oppose current, are color-coded, and connect in series (Rt = ΣR) or parallel. Current-limiting resistors protect LEDs.

A Simple Over-Voltage Protection Circuit for LED Drivers This boost circuit implements current mode control and senses the LED current via resistor R14. The output voltage is boosted to just over 30V ...

Holes were drilled at those marked locations, the LEDs inserted and hot glued into place. Each LED has its own current limiting resistor soldered in a series configuration.