If you cast Magelight at a living target, they will have a glowing light floating around them, similar to that created by the Candlelight spell. This is not an assault, but it will alert hostile targets to your presence. It can be useful to "tag" enemies, or keep track of your follower.
You can only have up to two Magelights active at a time, one cast on a living target and one cast normally. Having a second one of either type strike its target before the first has expired will negate it.
This may be better for stealth than Candlelight, because you can remain in the shadows while your target is well-lit and easy to see, though your location may still be revealed if you are seen or heard casting it.
You can cast this spell at a wall while sneaking, and hostiles will investigate. You can then sneak past them or move in for a backstab (it can also be used to get an enemy into a better position for a sneak bow attack). It is advised that you have acquired the Quiet Casting perk.
Occasionally the game may freeze when cast upon an NPC or creature. ?
The game can freeze if you cast Magelight at a surface a long distance from yourself, such as the ceiling of Eldergleam Sanctuary. The game will freeze when the ball of light is almost to its destination, or just as it sticks to the surface. ?
This spell can grant extremely large amounts of Alteration XP when cast from certain locations, such as just outside Solitude at a nearby mountaintop. See the page on Alteration for more info.