If the battery provides 4.5 volts and the led I want to use takes

if battery voltage is higher than led forward voltage a resistor is required.
the resistor value will set the power the led will use. try a value that is bright enough, not too bright.

>>948775

this is something that you shouldn't worry about

for a standard jellybean LED just throw in 1k unless you are working with unusually high power. otherwise just get a 10k pot, and test it.

Use a resistor to drop the extra 1.5V (and limit current).
Resistor_Value = 1.5Volts / LEDamps

So an LED rated 20mA would need a R of:
R = 1.5/0.02 = 75ohms

>>948814

it's hard to get a 75 ohm resistor

just throw in a 500 ohm

or hell, even 1k would probably work

>>948822
500 ohm would reduce the current to 3mA.
68 & 82 are both common values.
Even 100 would be fine. (15mA)