“There’s many a time when you want to connect a white LED to a microcontroller operating from a 3 V supply voltage. Unfortunately, this doesn’t work and your nice white LED only lights up feebly or not at all.
Why does it work perfectly with red and green LEDs, but not with white? A bit of data sheet research reveals the reason: white LEDs have a forward voltage of 3.2 V, so a 3 V supply is simply not enough to let them light up properly. The advice you often see in online forums is to use a boost converter to generate a higher voltage, along with a transistor switch to control the LED. For just a single LED, this seems like a lot of overhead.
The good news is that there’s an easier way. And it only needs one inexpensive component: an inductor, which costs next to nothing. If you wire it up right and drive it the right way, your white LED will light up nicely — and this even works with a microcontroller supply voltage as low as 2.5 V. Magic? Not at all.”