Chandeliers were first introduced by the wealthy in the medieval period, often carried on posts and with eclesiastical relevance, they were used to carry candles. During the 15/16th centuries more complex designs were introduced and became a form of status, often carried thro the streets to a party or gathering of wealthy merchants.
By the 18th C ormolu was introduced and chandeliers began to take on more elaborated forms, Murano chandeliers were the result of the glass blowing excellence of the artisans in Venice and these were often used to light the insides of theatres. We cannot conceive of how dark it must have been and how magnificent candle chandeliers in groups must have looked.
By the mid 19th C gas was introduced and gasoliers were common, these can be seen today and identified by their wide central tubing and hollow arms, which later became useful for passing through wiring.
Today antique chandeliers unless they are very expensive indeed (and then often re-blown) date from the mid 19th to early 20th C, after that they may be termed reproduction which is easily indentified by poor moulded glass without much lead content and rather clunky metal work. Some lighting made during the Deco period is fine and beautiful.
Styles are numerous.
Tent and Waterfall - mostly early 20th C and composed of a tent type top and several tiers of waterfalls below sometimes with arms and sometimes not ( usually later if lit internally )
Tent and Bag - again in tent format at the top and as a 'bag' of crystal octagons or pear drops below
Glass armed chandeliers - Baccarat with solid arms and needing to be wired over, English glass armed the best by makers Perry and Co and costing more than a ransome ( may also be old gasoliers ) and many variations of the same from Ireland, Spain, Belgium and Italy. All have candle carrying capacity arms which point upwards.
Electroliers - generally made for electricity often in the Edwardian period and often with lights pointing downwards.
Later lighting - short drop lights which were made 'in an earlier style' for lower ceilings, usually post 1950 this inclides hotel lighting, a great deal of which is on the open market today after refurbishements, some of it extremely good quality, some of it not.
A good chandelier in whatever style is always beautiful and will fill a ceiling space elegantly.