Moonbrighten, A System-Agnostic Spell

Moonbrighten

Description:  A simple incantation that can only be spoken in the light of the moon.  Alternately, it can be cast upon a single silver coin or disc, no more than two inches across.  Most experienced casters can master the spell, although it's beyond mere apprentices.

Effects: Moonbrighten has two possible effects, depending on which casting option is chosen.  If cast on a suitable piece of silver, that object shines with the light of a full moon as seen on a clear night.  This illuminates as well as a mundane lantern without generating heat and cannot be extinguished (although it can be covered up, hiding the glow).  The light has the same effects as the actual full moon would for all purposes, including were creatures, certain fey, and magical writings that can only be read under moonlight.

If cast without using a silver focus under the light of the moon, that light will be multiplied threefold everywhere within one hundred paces of the caster.  Depending on the phase of the moon and intervening cloud cover the effect varies somewhat, but even the very smallest crescent will be as bright as a full moon under similar weather conditions, while a half moon is nearly as bright as day.  A full moon will be so bright its dazzlingly painful to look upon, and weres and similar creatures will not only be forced into their animal or hybrid forms, they receive a 25% bonus to any damage inflicted by them while taking 25% less damage from all sources except silver.  Other creatures with lunar associations may be driven into bouts of manic activity or seem to be drunken while under this augmented moonlight.  Depending on the nature and inclinations of such creatures they may either flee the zone of the spell or seek to remain in it, perhaps even abducting the caster to ensure they stay in the light as long as possible.

Both effects last until moonset or sunrise, whichever comes first.  The death of the caster has no effect unless their body is utterly destroyed.

Possible Origins: This magic almost certainly began as a prayer to one of the lunar deities, although which one varies from culture to culture.  It can be used by almost anyone capable of employing magic, either arcane or divine, the exceptions being those who've somehow earned the disfavor of such a deity and, surprisingly, any were creature.  The latter can learn the charm but attempting to speak it sears their tongue like licking silver and spoils the spell.

Complications:  Triggering were-creature transformations or attracting some fey creatures are the main risks, but flooding an area with brilliant moonlight may annoy people who are trying to sleep.  The enhanced light doesn't scatter or reflect beyond the bounds of the spell, so people beyond that area most likely won't notice it was cast.  The center of the spell effect isn't obvious, so people or creatures trying to locate the caster may have some hunting to do, especially if moving rapidly.