Modern electronics industry has developed very efficient LEDs with nice and fancy colors (“true green” , “cyan”, and “blue”) based in InGaN technology, or similar. Some of these LEDs are specified as having forward voltages of 3.2 to 4.2 V. Here are examples of such LEDs, Kingbright WP7104PR51C/A, or surface-mount APT3216VBC.
But the usual MCUs are powered from 3.3 V supply, and the GPIO output is usually at 3.1-3.2 V, which seems to be barely enough to drive these LEDs . How can I use these LEDs as indicators of some signal statuses, or power rail status? Do I need a series resistor R1 here?
If yes, how do I choose its value?
DISCLAIMER: This "question-answer" comes as elaboration of the original question "Is there a point in adding a 1 Ohm resistor to this LED circuit?", to address the particular use case of LEDs as logic state indicators.