How can a power a single led with a power supply?

I want to power a single led with a power supply from the wall. I use just a single blue led for a nightlight for my aquarium. Anyway, how it runs now is the led is a 3.8v and it is connected to a resistor, then to some lamp cord like copper wire, and then to a 4 %26quot;AAA%26quot; battery holder with on/off switch that i got from radioshack. I dont want to keep using batteries to power the led since it will cost a lot to keep changing batteries when i want to run it on average 6 hours a night. It is just my little diy project i am trying. I just want to know how to wire the led to a power supply to the wall. I know nothing about electric as far as that. Like can use a cell phone charger or some other type of plug? I don't know. Just tell me what parts i need and how to do it. I have a soldering iron at home, so i guess thats a plus.How can a power a single led with a power supply?
You'll need a transformer with the correct output voltage. Radio Shack should be able to help.

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