I have a collection of various LED units I have no specs on. What is a 'safe/typical' resistor to use with them? Power supply could be anywhere from 3 to 9v...
I keep a 1.5V AA wired with a 1k resistor handy for 100% sure-fire safe polarity testing. Even on a 3.6Vf/3W LED bead there is a faint glow good enough for indicating go/no-go testing.