What resistor should I use after changing this LED from using 220v to using 5v arduino?

Question

I bought these LED things without realizing they require 220v (I assume that's for European mains wiring, right?). Anyway, I took them apart, and inside is a disk type LED, with a resistor, and a capacitor. The resistors were all 1000 ohm resistors, but the capacitors all had slightly different writing on them. 400v 470k, CARLI MTF 104K 450V 4E30 A02, CARLI MEH 104K 400V 5B27 A02.

I took the capacitor and resistor off of one of them, and it runs fine on 5v, I tried it with no resistor, 10ohms, 100ohms, 220ohms, and 330ohms. All worked fine, obviously each was a little less bright, but my concern is ruining the LED if I don't use the correct resistor/capacitor with the new voltage.

I'm quite new to this kind of thing. Usually I use regular 5mm LEDs, and I put either a 220ohm or a 330ohm resistor with them (no capacitor).

My question is, what resistor should I use with these LEDs to make them as bright as possible, but still safe from destroying them? Do I need a capacitor?

Thanks

Answer 1

Typical capacitive dropper setup. They use the resistor and capacitor to drop the 220V down to the led needs.

Cut the existing resistor and cap off. Replace the resistor with r = (V source - Typical Forward Voltage) / typical forward current for your color led.

Assume 5V Vs, 20mA If.