One of first things that you might learn as electronic hobbyist is that you should have 20 mA running through your indicator LEDs. For example, if you have 5 V power supply and your LED has voltage drop of 2V at 20 mA just give it 150 ohm resistor and you are golden.
And that is wrong. This recipe was valid 20 years ago but it is not something you should follow these days. If you have 20 mA coursing through LED, that is BRIGHT as hell. When you work in dark, every look at such device blinds you for minutes.
Don't misunderstand me, I like to see some indication that device is alive but 1 mA or less should do the trick. These new LEDs are extremely efficient with their output and, while they still specify their current at 20 mA (or even higher), they will be bright enough at lower currents also.
PS: This rant is only about indicator LEDs; if your device needs to light-up the room, so be it.
Oh yes, that brings me back to the days I was tinkering with LEDs and power supply…..Resistors? well that’s for girls I thought and connected red LED directly to 5V (later I found it was 7V not that it matters). Talking about bright as HELL – first I saw a bright flash then came the BANG! It was the only time I made red LED shine WHITE :)
:)