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RE: 12V LED polarity? - geek2me - 04-24-2017

(04-20-2017, 08:04 PM)woodmats Wrote: a basic LED's lights up when current flows in the forward direction and no current flows with the opposite polarity.

Current still flows in the reverse biased direction, but the current is much smaller.  Typical LED may have a 16 mA current when forward biased and 100 uA when reverse biased.

RE: 12V LED polarity? - geek2me - 04-24-2017

(04-20-2017, 08:43 PM)Robert Adams Wrote: Also to add the actual leds typically run at 5v they are not 12v units.

Voltage drop across a diode is nominally 0.7 V, can range up to a volt or two for some LEDs.  The purpose of the series resistor is to limit current through the diode.

If you connect an LED across a 5V supply with no resistor, the magic smoke will come out.

You may be thinking of diodes that have the resistor in the same package or contain more than one diode element in the package.

RE: 12V LED polarity? - Foggy - 04-24-2017

I finally got a reply from the manufacturer. On the lights in question the black is negative. Other lights that I will be installing the white is negative. [marked or in the sales description] So I will draw up a wiring diagram to follow.
Yes

RE: 12V LED polarity? - EricU - 04-24-2017

(04-24-2017, 01:34 PM)geek2me Wrote: Voltage drop across a diode is nominally 0.7 V, can range up to a volt or two for some LEDs.  The purpose of the series resistor is to limit current through the diode.

If you connect an LED across a 5V supply with no resistor, the magic smoke will come out.
a typical power LED has a Vf that is somewhere in the 3 to 4 volt range.  Many of them will survive 5 volts, but life will be shortened.  The red power leds seem to be more fragile.  Of course, a tail light may have the older style leds with lower Vf. If you look at the 12v white led tape that you can get, there are not that many devices running across the 12v supply lines, 3 or 4, depending on the tape.  The tape may or may not have current limiting resistors, it's not strictly needed in that case.