3x57xx Bulbs Demystified

While the 3157 family of bulbs is pretty ubiquitous these days, it can be difficult to sort out what the differences actually are. Here’s a quick legend:

3057	32 candlepower at 2 feet
3157	32 candlepower at 3 feet
3357	40 candlepower at 3 feet
3457	40 candlepower at 3 feet, High-Heat Base
4157	32 candlepower at 3 feet, Extra Long Life
4114	32 candlepower at 3 feet, Ultra Long Life

K	Krypton Filled (Long Life)
LL	Long Life
NA	Naturally Amber (the glass of the bulb is actually amber)
A	Amber (clear glass that has been dipped or painted amber)

Of course, this is all nearly useless information these days considering LEDs have advanced to the point that they’re substantially brighter than incandescent bulbs, last much longer than incandescent bulbs, and don’t actually have a bulb to worry about how it was colored. Long story short, you probably want to get yourself some 3157 LEDs and never worry about replacing bulbs again.

If you do choose to go with LEDs, make sure you know whether your vehicle has CK sockets or not. Incandescent bulbs don’t care if you have CK sockets as polarity doesn’t matter. LEDs, however, very much do care. The difference between the two is how the pins are laid out in the socket. If you’re looking at the bottom of the T25 wedge with the plastic piece horizontal, here’s the arrangement:

3157		3157CK
Ground	Low	High	Low
Ground	High	Ground	Ground