ThreeJS position light at angle and distance from center

Question

I'm trying to learn the ThreeJS positioning functions, but I'm not quite getting there.

I have a light and an animation loop. I want this light to be at a fixed angle relative to the camera pointing towards 0,0,0.

I can make the light come from the camera angle itself like so (in animation loop):

rectLight.position.copy(camera.position); 
rectLight.lookAt(0,0,0);

But I don't want it to come from the viewer's perspective, I want it to come from somewhere else relative to it, and at a set distance from center.

So I think it's camera angle +/- some degrees/radians, and then a fixed distance.

I've tried adjusting the coordinates relative to the camera position, like y += 25, y *= 3, and such. Everything I try gives me some whacky light placement motion I don't understand. I'm sorry, 8th grade geometry teacher, I should have paid attention.