Electronic – Similar LED, higher voltage drop, less bright


I was measuring voltages in my circuit, and noticed something strange.
I have an array of 8 LEDs. Each of them is in series with a 220 Ohms resistor. The circuit has a 5v source.


simulate this circuit – Schematic created using CircuitLab

The LEDs are all the same model. They all have ~1.90v across them. All but one, which has ~2.1v. At the same time, that LED has an inferior brightness. I can interchange this LED with another anywhere in the circuit, and it still behaves the same.

Is it normal / usual ? Does it mean I burnt it somehow or made a mistake in my circuit ? What's with the inferior brightness when it drops a higher voltage ?

Best Answer

If there is a higher voltage across that LED, than it is drawing less current because the voltage across the 220 ohm resistor is less (5- 2.1 or 2.9 volts compared to 5 - 1.9 or 3.1 volts across the other 220 ohm resistors. Thus it is drawing 2.9/220 or 13.2 ma while the others are drawing 3.1/220 or 14.1 ma. Generally, LED brightness varies in step with the current through it. That being said, the difference between 14.1 and 13.2 is not much so that the brightness difference shouldn't be that much. Do you have the specs on the LED? It may be perfectly normal for that particular LED to have that variation of voltage drop. I don't believe you damaged the LED nor have any circuit errors.