Both, actually. The problem is that you are thinking of light just like regular species, when it isn't. When discussing the mechanisms of sight and species, the philosopher always considers light and species separately, although they are related concepts. Species cannot transmit through darkness, therefore you need light to see species. However, you can see a light through darkness (that campfire on the hillside, or the moon), so when you see a light in the dark you cannot be seeing its species. There must be a qualitative difference here between light-producing objects and light-dependent species.
The Aristotlean view was that light came in two* varieties. The terminology wasn't used consistently by everyone, but most authors (and I'm using Avicenna here) distinguished lux from lumen. Lux is the brightness that one observes in fire or the sun; the luminous quality of fiery objects by which they are themselves percieved (when a transparant medium intervenes). So when you are seeing a campfire in the dark from several miles away, you are seeing its lux, not species.
However, luminous bodies produce lumen, which shines out from them and falls upon non-luminous objects and causes them to become visible (i.e. emit species). So lumen is the effect of lux on the adjacent medium and objects. It is lumen that allows species to be transmitted. Some authors viewed lumen as a non-material 'fog' that filled illuminated areas and permitted the transmission of species, and this is from whence the statement in HoH:S came; it just didn't make the elaboration that the 'light' referred to was lumen. Averroes made it clear that It is important that lumen is non-material, else species would become intermingled when they crossed. Pure forms have no matter, so don't interact.
*well, three really. There was also radiositas which is a glow emanating from non-luminous objects, but let's ignore that just now!
The most likely manifestation of Hermetic magic (in my opinion) is that CrIg creates magical lux, or magical objects that have lux like a fire. The lumen that radiates from these luminous objects is non-magical. This is by analogy with other Forms; CrAn creates a magical wolf which then radiates non-magical species. A magus with Magic Resistance is therefore still illuminated by a magical light source; and a light source created in a Ring still radiates non-magical lumen beyond the bounds of the Ring.
(Sorry for the long-winded post!)
Mark