As a game matures over time certain aspects change. Character classes expand and contract. Spell lists grow and shrink. Dice come and go... and like Becky Conner, some things change so much that you might not even recognize their earlier casting. Dancing Lights is one such example. A spell that fell into the Alteration school of magic as a first level spell has now become a cantrip belonging to the Evocation school.
In first edition Advanced Dungeons and Dragons this first level Alteration spell required vocal, somatic and material components. It had a range of 4" + 1" per level of the caster (40 feet plus 10 feet per level in 5E terms) with a duration of two melee (minute) rounds per level of the caster. The caster would be able to use this spell to create one to four lights that would appear to be torches or lanterns when viewed from afar. This spell did not see a lot of use by new players but it was very effective in the hands of a skilled NPC or player to lay traps or otherwise trick opponents.
In the long years since this spell graced the pages of the Player's Handbook in the late 70's it has fallen from level one to level zero, becoming a cantrip. It didn't happen right away, but it did happen.
Dancing Lights in Second Edition of Advanced Dungeons and Dragons remained essentially the same as its First Edition parent. Third Edition is when the spell changed from Alteration to Evocation along with its demotion from a first level spell to a cantrip. Since Dungeons and Dragons went straight from 3.5 to Fifth Edition I will relate the basics of how the spell operates now.
Dancing Lights is an Evocation cantrip that requires somatic, vocal and material components. It has a duration of one minute and a casting time of one action. It has a range of 120 feet and can create one to four lights or the lights can be combined into a vaguely humanoid form of medium size. As a bonus action the lights can be moved up to 60 feet (within range) but no individual light can be more than 20 feet away from another light in the group.
To me, this spell should have always been part of the school of Illusions. It was available to the Illusionist class but it was never categorized as being part of their school.
You might be wondering why anyone would waste a first level spell slot on this one, a fair question to ask. Forty years ago no self respecting player would waste a spell slot on this, mostly because forty years ago everyone played a character that was not much more than a murder hobo. We were all devotees of the Ash Ketchum school of adventuring. Every now and then though, an enterprising DM would surprise their players with this spell and use it to lure them into a trap.
DM: The corridor ahead of you branches in a Y formation. You see what appears to be the shadows cast by torches or lanterns further down the left corridor.
Players: That's probably where the bandits are hiding out. We creep down the passage, arrows knocked and ready to let loose.
DM: You get about thirty feet down the corridor when the lights suddenly go out, as does your footing. A pit opens up beneath you! You hear laughter from behind as the bandits suddenly appear from the other corridor, accompanied by a robed figure.
Dancing Lights used to distract a group of PCs
Dancing Lights is very useful when cast as a tactical spell. While it can not directly damage it can be used to trick the unwary. When coupled with the old school Audible Glamour spell even a party of experienced PCs can be tricked.