I did some experimenting with some LED pucks that I have. In the background of the videos you can see the power supply where I range the input voltage to the pucks from about 6.5Vdc to 15Vdc. This is done in a constant voltage mode (green numbers) allowing it to pull the amps that it wanted (the red numbers)
What you will see is how some pucks are designed for automotive use and some are not. If the light output / brightness changes with the voltage like the 3rd one, its not going to survive long in service when used in an automotive environment since its not controlling the current going across the LED. It was actually one of the lowest lumen parts but since it had no controls it pulled just as many amps as the other LED samples.
Even though the 3rd one was sold by an RV dealer (Foretravel parts), its the wrong type for the job. So make sure its intended for use across a wide range of voltage, like 9Vdc-36Vdc (at least for the puck lights).
First up is an advertised 1W cree with a buck driver. Actually the ad does not say what the driver is but claimed a wide voltage range. You can see that the output light does not change with voltage and has a distinct shut off level.
Next is an advertised 3w cree with a buck driver. Again the light output does not vary with voltage and has a shutoff point as well. These are what I'm currently using as they fit in our small dome ceiling lights with the reflectors still in place.
Here is one from a RV dealer (Foretravel parts), no buck driver so you can see its light output swing widely as the voltage changes. This one is a cool color where the previous two are in a warm white. It was also the most expensive one of the bunch.
This on is one we had in the coach for the last 4 years, its buck driver is now shot. The light levels jump around almost randomly, smooth ramp in some areas, constant in others, jumpy in others. This was a "warm-ish" white, probably 3 or 3.3k, which a few years ago was as good as you could do.