Night Faire occurs in late summer early fall upon the full moon (or blue moon). The Early Fall is the best as the sun is going down earlier so the festivities can start earlier. And if the weather, generally, will permit, the night of the Blue Moon would be perfect (especially since it is a large blue moon.
It a tradition in the southern and western parts of the region where the fall weather is "better". It comes from an "older culture" has been long displaced by the current culture. (To use an Earth analogy, it was a celtic holiday, rather than a christian one for example). The holiday is sometimes followed in other parts of the world, as it has been transplanted there by travelers and transplanted people.
The holiday is a time of merriment and fun, with an association of shadows and illusions. It is a time of gaity and fun. It is made all more exiciting by the flickering lights and shadows to hide in while cuddling a partner. The Faires is mostly a night time market faire. Apple based foods and fried food stuff seems to be a dominant theme (though some places have common feasts). Every game and race that can be held at night is held. Mazes are set up made of straw bundles and temporary fences. The entertainments tend towards music and shadow plays (puppet shows that are back lit against a screen. In more properous places, dancer/actors are used). (It is the busy season for Chrisia’s ShadowShop and similar places).
Decorations and events having to deal with light and fire are everywhere. If sparklers are available (or tiny light magics) they will be prevolent. Bon Fires are very common events in a faire. People like to carry lights with them. Traditionally ball candles round candles (with the wicks in a carved in area) that burn down and "glow" as balls are carried by people. Lanterns made of turniops or squashes (like pumpkins) are oftens used instead. Miner lights are the common light in some areas.
(SO are the barrels full of water with buckets attached to them. Sometimes people put apples in those buckets, but you can’t have one.. unless take it out without touching it with your hands.
Long ago there was a tradition of magical spirits, feys, and ghosts. It was a night festival, a time for mortals and the mythics/ spirits would mingle. The stories go that ancient pacts made it the one night that people did not have to fear the mythics as they could not harm (physically) harm anyone. However the trade off was they were allowed to waunder the world. However the various stories related to the Night Faire vary from region to region. The Night Faire is the descendent of this. Sometimes these motifs are included in modern faires. So you will see pictures of mythics and such, crafts focusing on them, ghost shaped cookies, and so on.
Jacks of the Lanters and Glowing Balls are traditional images for ghosts and spirits, thus continuing the old motiff as well as providing light.
In fact, the tradition of lighting candles on the graves of departed family members and leaving cookies for them was part of the ancient tradition as well.
One tradition from the ancient faire that continues to this day is the wearing of masks. People like to wear mask (wigs are also an option). Most people wear domino or tiny masks. It is not like nobody does not know who is who in a small town, but the mask lets you "pretend to be someone else", especially if you wear other garb. The sumptuary laws are ignored, you can wear anything you can get your hands on. (thus older noble dresses find their way to servants). A few silly folks will wear costumes, pretending to be a wolf or a ghost or even a priest.
People travel in groups mostly (as they are not stupid). They stay along the brighly lit paths. Luminaries (candles in small sacks with sand in the bottom line paths. Did we mention the commpon stone walls and roofs in these parts, just to avoid fire. However the water barrels are always around.
It is also a time for romance and other activities frowned upon in church. The shadows are convinient. It is seen as the last chance for romance and a great time for just having a fling.
One traditional from the older times also continues. The entire faire area is surrounded by blessed salt (or an area defined by salt pots) to ensure that no untold magic or wyldness comes near.