Resistor for LED?

I purchased a Dialight 657-2503-103F dome top LED. I am using 12 V DC to power it and it appears to have a 12V forward voltage. Does this mean I don’t need a resistor to limit the current to it? If I need a resistor, what size should it be?


You should definitely be taking steps to limit the current. If the LED really does have a 12V forward voltage drop, then you likely should be powering it with more than 12 V, and you should select a resistor such that (VIN - 12 V)/R equals your desired current (I’m not sure what the appropriate current is for your particular LED).

By the way, if your voltage source will change over time (e.g. you are using a battery that will be discharging), you probably want a voltage much higher than you LED drop. Otherwise, the current (and brightness) will change significantly as voltage changes.

- Ben

Hi, a quick glance at the data sheets shows it already has a limiting resistor built in. So you are good to go on 12v.