# What resistor?

I've got some lovely LEDs, they're 2.5-3.5V with a forward current of 25mA. I've bought them because they're bright.

An LED resistor calculator advised I need a 1/8W 82 ohm resistor.

These are a bit tricky to find locally.

Q. Would a 1/4W 100 ohm resistor cut the mustard instead? i.e. It doesn't matter that it's rated for a 1/4W instead of a 1/8W? This won't make any difference, right?

as I would need to buy this resistor,

Q. I have these resistors: 560 Ohm, 2.2k Ohm, 10k Ohm.

If I use the 560 ohm resistor, the LED won't be nearly as bright as when the new resistors arrive, right?

Dane: I've got some lovely LEDs, they're 2.5-3.5V with a forward current of 25mA. I've bought them because they're bright.

An LED resistor calculator advised I need a 1/8W 82 ohm resistor.

These are a bit tricky to find locally.

Q. Would a 1/4W 100 ohm resistor cut the mustard instead? i.e. It doesn't matter that it's rated for a 1/4W instead of a 1/8W? This won't make any difference, right?

Not much, I would suspect you would hardly be able to tell a brightness difference between 20ma Vs 25ma. Wattage difference is not a factor other then taking up a little more space.

as I would need to buy this resistor,

Q. I have these resistors: 560 Ohm, 2.2k Ohm, 10k Ohm.

If I use the 560 ohm resistor, the LED won't be nearly as bright as when the new resistors arrive, right?

Correct, it would light up, but at very reduced brightness. Lefty

OK - the resistor is in the circuit to limit current. A larger value will allow a lower current to flow. As long as it isn't too big the LED will light. With a larger value resistor the LED won't be as bright, because less current is flowing. the 1/8W, 1/4W is how much heat the resistor can get rid of. A larger value there won't hurt you in any way. A smaller value than recommended will get HOT and possibly fail.

The LED wants 2.5 V at 25mA - Ohms Law - Voltage = Current * Resistance - E = I * R - 2.5V - 0.025A * R or to re-arrange - R = E / I or R = 2.5V / 0.025A or R = 100 Ohm.

The 82 Ohm resistor will have slightly less voltage drop and slightly higher current and the LED will be brighter..