spec-tral  / 'spek-truhl/  Spelled Pronunciation[spek-truhl]­adjective

1. of or pertaining to a specter; ghostly; phantom.

2. resembling or suggesting a specter.

3. of, pertaining to, or produced by a spectrum or spectra.

4. resembling or suggesting a spectrum or spectra.

For the purpose of this article I will talk about a spectral highlight as being a reflection of a light source, because that's what I learned from hanging around other photographers, they claimed to have made the phrase up.

The big deal about this for me is finding the angle of incidence. What that means is where do I put my light to create a cool reflection in my subject?  Now we're talking, cool reflection of a light source. I'm not so sure I would go so far as to say "ghostly phantom" reflection of a light source but why not if you want to and can?

Anyway, the first thing that gets into my head when I'm looking to create a cool highlight is I get a visual of an aerial view of a pool table.  That's how I visualize the angle of incidence. That is probably a result of being dropped as a child, but it helps me visualize and guess where I might go to place the light. If you were not dropped as a child or perhaps dropped on a different surface, the easy way to find a cool highlight is this. Frame your subject, place your camera on a tripod, put an undiffused light source in front of the camera lens. Walk around your subject until you see a tasty highlight pop. That's where you place your light, right about where your eyeball is. Spotlight, softlight, floodlight? You decide, how does your subject respond?