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I've been researching this and cannot find any comprehensive guides. I'm looking to replace some incandescent bulbs soldered to pcb's inside my cars console. I've found some through-hole clear LEDs that have built-in resistors and they work but does that make them actually 12v? When I put a volt meter across the connections it reads the same output voltage as input voltage so I don't see the resistance happening. I've also looked for SMD leds with built-in resistors or 12v version but I don't think they exist. I don't really have room for resistors and looking for options.

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  • \$\begingroup\$ Take the voltage across LED and GND.... Not across two LED pin... \$\endgroup\$ – 12Lappie Mar 23 '17 at 19:20
  • \$\begingroup\$ The LED voltage drop depends on their colour (1.8 - 4.0V), to make them 12V compatible they need a series resistor which is built into '12V LEDS'. \$\endgroup\$ – JIm Dearden Mar 23 '17 at 19:20
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    \$\begingroup\$ There's not really such thing as a "12V LED". Anything labeled and/or sold as such is really a 'normal' LED with a series resistor 'built-in'. Unless you can access the connection between the LED and the resistor you won't measure anything other than the supply voltage with your meter. \$\endgroup\$ – brhans Mar 23 '17 at 19:24
  • \$\begingroup\$ @brhans Thank you! This helps clear up some issues. When purchasing leds it's difficult with all the marketing terms they use. Is there any compact way to use a resistor and led in a surface mount configuration? \$\endgroup\$ – user3953989 Mar 23 '17 at 19:30
  • \$\begingroup\$ I've never seen a SMD "12V LED" or a combination LED+resistor in a single SMD package. If you're good with a soldering iron & tweezers you could try balancing an 0805 SMD LED on one of these mounted on edge to make a T shape ... \$\endgroup\$ – brhans Mar 23 '17 at 20:09
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AFAIK there is no, or at least no common, led diode that is typically 12V forward voltage by it self. 12V led are modules that consist of some combination of diodes and resistors to make them suitable for 12V power applications without needing extra current limiting. This may be a single led with resistor, or multiple LEDs with resistor, or maybe a constant current IC. Some may have extra features like reverse protection or any direction input.

But they are not bare diodes.

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