The math formula is Vsource - VLED / ILED = R. A typical 5mm red LED may be 1.8v and 20mA so running them on 5v circuit: 5 - 1.8 / 0.02 = 3.8/0.02 = 190 ohms. (probably 200 as the nearest common value resistor) But that only works if one wanted to have LED at max rated spec or to drive LED at speci…

Computing resistor value for LED

MarkT September 29, 2017, 10:42am 6

wilykat:
Any idea or am I stuck guessing value using variable resistor then measuring them?

Subjective brightness is, er, subjective. How to calculate that??

Topic		Replies	Views
Correct calculation of resistor value when connecting LED? General Electronics	8	4481	May 6, 2021
Resistor General Electronics	11	1840	May 6, 2021
Simple question about resistor for LED General Electronics	19	7175	May 6, 2021
Another learning question about resistors General Electronics	7	2316	May 6, 2021
What voltage do I use for calculations? Interfacing	4	1314	May 6, 2021