imo a spot light is the wrong tool. you light cars with big lightformers (been into photography years ago and had the chance to follow some car photographer guys around). but this is what creates these streaks and strips that give the car character and shape.
in threejs there are no rect lights that are feasible runtime, so make your own inside an environment map. few people seem to know about it, but this is the cheapest, easiest key to good looking scenes. here’s an example, this is how a car looks with point and spotlights:
and this happens when you add an environment map with light formers:
no light in threejs will give you that kind of look. only environments. the process is explained here: Live envmaps and getting realistic studio lighting almost for free it is super easy.
as for spot lights, they’re not like in blender, volumetric. so if that’s what you want you need to figure out shading. here’s an example for that:
the article which explains how to do that is here: john-chapman-graphics: "Good Enough" Volumetrics for Spotlights