The attached is about the cheapest linear regulator that you can get for a rear/brake LED light.
Its for an executive car.
Those BJTs need to be SOT89's.
The PCB will either need to be bigger than an smps one so as to be able to pass out the heat, or the pcb will need to be mcpcb. So already we have extra expense due to it being a linear regulator.
Another point is that to save on components, only one actual string of leds gets its current regulated..the other strings are "regulated by proxy", and as such one assumes excellent thermal coupling between the BJTs and the LEDs, and also assumes that the BJTs all happen to be matched, -something that no manufacturer of BJTs guarantees for any given batch of BJTs.
Note that despite having a Car battery to power it, the most we can have is three in series, since in cold ambients, the red leds may have voltages near 3.3V, and with the supply cable volt drop, the supply at the lamp may well not manage that, and especially if a reverse polarity diode is used...So we end up burning off the excess power....If the driver is in a downhill traffic jam, then he/she may keep their foot on the brake pedal for a long time, and it'll be on full power.
Regarding incandescent rear/brake lights, they are a different story, incandescants don't suffer from heat the way that LEDs do. Incandescants chuck out a lot of their energy by means of infra-red, whereas LEDs almost totally rely on heat being convected away from them, or conducted into their footprint copper....Another point is that incandescent lights come as bulbs, which are easily popped out and replaced, the attached led linear regulator comes on a pcb/heatsink assembly, and needs the car to go into the garage for a good day at least for dismantlement, and replacement....all the more reason to use a cool running smps driver which will keep cool the internal ambient and make the leds last longer.