   Lighting effects, light rays and glow of light source
  How do I actually go about making the light source glow? For example the car headlights.If I place the spotlight source at the position of the car headlights, it lights the road ahead as expected, but the headlamps of the car is not lit up or glowing as in real life. How should make the lightsource actually lights up an glow?How is realtime light rays achieved? isn't raycasting/marching slow?   
  search for HDR, or if you want something simpler then its glow post-processing effect. for light rays its called volumetric lights.   ;  If HDR is too expensive, you can also fake it with in LDR with a simple bloom, but you have to be careful not to add too much, or else the scene looks like one of those cheap x-movies from the 1980s.Taking the square of the original pixel value as input to the blur function is a relatively inexpensive way of reducing the contribution of the darker regions, so only really bright areas are blurred out, which is what one wants.If that is too expensive too, you can still fake the light glow using a halo/corona sprite (using additive blending, possibly modulating by the light source's visibility). It is nowhere as good of course, but extremely simple and runs on 10 year old hardware.   