I was looking at some pics from a recent trip and some of the lights reminded me of the good old Cokin star filters.  Instead of a halo or glow there was a distinct star effect.  Looking closely at the filter I keep on the lens I noticed that there were a load of micro scratches.
Essentially a star filter is a bit of glass with geometric scratches on it, and that is what the filter had become over time - about three years or so. If the lens was filterless I'd be looking at a very compromised camera or lens.  Either way very expensive to fix.
Pic below shows the issue (squished down to fit here) - there is a distinct star effect on the right hand light hitting the lens as opposed to the indirect light on the left. It is generally confined to incident light.
Anyway don't put cheap filters on your lens.  They'll reduce light transmission, add flare, chromatic aberration and ghosting. Stick to proper brands from proper outlets. I've just ordered a Hoya Ultra Pro as a replacement.
As ever comments welcome as to filter or not has various views.
Edit: Exif data says f2.0 at 1/60th if that's of interest.