Problem understanding led's behavior

[Tipsy]

audioguru That is an excellent reply, thank you very much! I learnt something new.

I (wrongly) tend to class LED's by the button battery voltage that lights them up, in this case a 1.5v would not but the 3.2v did.

I created an array of 12 white LED's, making three rows of four leds in series - each row being in parallel, if that makes sense? (I was wrong, the battery is in fact a 12v 17Ah, found in those cheap booster power packs). The original bulb had blown so thought LED's a better alternative. I must have got lucky (so far) as they work well. If they do eventually burn out, I now know how to rectify it. Thanks again, you're a good tutor IMHO.

Apologies to OP for hijacking this thread.

 

[audioguru]

A button battery is so small that its internal resistance limits the current to an LED.

 

[Sceadwian]

A lead acid batterys voltage will drop bellow the nominal 12 volts relatively quickly, you may just be working in a safe voltage area. Also diodes do actually have some bulk resistance, in series it does add up, although I'm not sure how much resistance you'll actually end up getting it's gonna be pretty low.

 

[QuietMan]

As a general rule never run an LED without a resistor or some other current limiting in series with it. LEDs, like all solid state devices, burn out quick. Fortunately, for the most part (and some major exceptions) they are cheap.

 

[birdman0_o]

**broken link removed**


As you can see, there will be a very small current if the voltage of the supply is not enough to get it into its forward conductive region. (The green area)