As a flashlight nerd and reviewer, I know a number of ways to control the brightness of an LED, and linear regulators are a fairly common one. It's important to

As a flashlight nerd and reviewer, I know a number of ways to control the brightness of an LED, and linear regulators are a fairly common one. It's important to note that a linear regulator can be designed to target a specific voltage, or a specific current. LEDs should be regulated with current for the reason you mentioned. One that I think would work well in cars is a fixed-current linear regulator like the AMC7135. There's no need to do anything fancy to control it; put a 7135 in the circuit and the LED gets 350mA. Two in parallel and it gets 700mA, and so on. More fancy is a linear regulator with variable current output. Linear regulators are a low-end option for flashlights, with switched-mode power supplies being preferred for their superior efficiency. A car has a lot more energy to work with and more mass with which to sink and radiate heat.