The difference between Light and Dark magic is one oft explored, but rarely set to paper. It is now time for that to change.
The simplest explanation is that Light magic is that of healing. This is not incorrect, but it is wildly incomplete. Light magic is indeed for healing, but mages who practice Light-magic are also adept at shielding, protections, and often are more capable at dealing in raw magic from Leylines and nodes than their Darker counterparts.
In addition, the natural magics are almost exclusively the realm of Light-Path mages. That is to say, thread magic, forge magic, green magic, and the like. The art of creating is widely, correctly, considered to be the realm of Light-Path mages.
This Path does have a number of notable exclusions. Most importantly, it is very rare for a Light-Path mage to be adept at combat spells. While some Light-Path spells can be altered for combat purposes, they remain distinctly different from true battle magic and are significantly weaker, per the magical energy spent to cast it.
(Personal note: there are several Light Mages in history who have made a talent of turning their power to both combat and healing, but they are rare. Usually, this feat is managed by spending significantly more power- overcasting if you will- in order to raise the power of their spells to damaging levels. Even so, they remain significantly more capable in the truest forms of their magic.)
The one exception to this is when they battle creatures born of Darkness, such as ghouls, demons, vampires, and their ilk. These creatures are inherently weak to spells that lend themselves to a Light Mage’s particular skills.
Healing can be hit-or-miss for most Light-mages. While it is a frequent specialty, it is not a universal one, and not all Light-mages are in fact even capable of healing. As I mentioned above, it is not uncommon to find Light Mages crafting in the forge, the stillroom, or the gardens.
There is, of course, the standing difficulty for all healers is that they cannot heal themselves unless it is truly life-or-death. There seems to be an instinctual block that saves their healing magic for others, and not for themselves. Healers in particular are largely unable to use their magic on living beings, although there have been rare exceptions.
(Personal note: The White Witch is the most famous of these, but as a Sun Elf, it is difficult to tell how much of her ability is inherent to her race, and how much is magical expertise. Regardless, she is possibly the most accomplished Light-Path mage currently living.)
Dark-Path mages are not, as many would assume, Dark in personality. Indeed, I would suggest that the name itself is highly misleading. As with Light-Path magic, Dark-Path magic is no more Light or Dark than the use in itself.
That said, the most common, and indeed most applicable, use of Dark-Path magic is in battle. It lends itself to combat extremely well, and is most commonly seen in mages who employ their skills as such.
While they are not as powerful as Light-Path mages, on the whole, Dark Mages tend to have more options open to them than their counterparts. No Path is closed to them, excepting only healing.
Battle magic is more powerful per energy spent on it. Attack spells come easily to Dark Mages, even though they are frequently less able to access the natural power. Where a Light Mage might be handling leyline power just out of apprenticeship, a Dark Mage would mostly be into their Mastery before being able to survive the flood of raw power associated with Leylines and nodes.
(Side note: there is a significant leaning between races. Elves, most especially Sun Elves, have a significantly higher instance of Light magic than humans. Orcs and goblins have a significantly higher instance of Dark magic than humans. Within humans themselves, there is some variance dependent upon the leyline activity near their place of birth, but it is unreliable, and largely unstudied.)
Dark magic does have the notable downfall of being uniquely vulnerable to true Dark magic. That is, to say, blood magic. Light-Path mages are entirely unable to use blood magic as it is direct anathema to their power. There have been no recorded instances of a Light-Path mage using blood magic, throughout our long-written history.
Young, powerful, Dark-Path mages are very often targeted by more powerful mages who are able to use the magic in their blood to fuel spells they could not cast alone.
(Personal note: The Mage of Black Fire is known to be one of the few who escaped such a situation, and has provided a rare treatise on the things he survived while under his Mistress’s control. After reading it, I admit to some amazement that he survived with his mind intact.)
As such, there is some distrust among Dark-Path mages. They are all aware of how slippery that slope can be, and police their own cautiously.
That said, even with the power difference between them, Dark-Path mages are most highly in demand. A mage with a healthy spellbook of combat magic will rarely go hungry and Master mages in battle magic will find their way to fame and fortune with relative ease, provided they are willing to go to war for their ruler.
In conclusion, I believe that there is a great deal more to explore within the magics of our world. We have only scratched the surface of the knowledge yet to discover.