PointLight = object
  position*: Point           ## a `Point` object holding the position of
                             ## the point light in 3D space
  color*: Color              ## the color of the point light
  linearRadius*: float ## a floating-point number. If non-zero, this «linear radius» `r`
                       ## 
                       ## is used to compute the solid angle subtended by the light at a
                       ## 
                       ## given distance `d` through the formula `(r / d)²`.
  

proc newPointLight(position: Point; color: Color; linearRadius: float = 0.0): PointLight {.
    ...raises: [], tags: [].}