If we look at modern dictionaries *chandelle* and *bougie* are indeed sometimes given as synonyms and used as such by lots of people.

But strictly  speaking *bougies* and *chandelles* are different objects, even if their purpose is the same.

*Chandelles* (candles) used to be made of tallow (*suif* in French) and sometimes (rarely) from wax. Tallow doesn't burn well and smells bad when hot. Candles made of wax became more widespread in France from the 14th century onwards because they started to import great quantities of wax from the town of **Bougie** (nowadays [Béjaïa][1]) in Algeria. And that's when the word *bougie* began to be used for wax candles in France.

In Britain wax also gradually replaced tallow in [candle making][2] but English didn't change the name as French did. 

So strictly speaking *chandelle* is a tallow candle, and *bougie* is a candle. 

Note that *candle* and *chandelle* both originate in the Latin *candela*. 

  [1]: https://en.wikipedia.org/wiki/B%C3%A9ja%C3%AFa
  [2]: https://en.wikipedia.org/wiki/Candle#History