How candles use cumbustion
Candles make light by making heat ,so they’re crude examples of what we call incandescent lamps (old-fashioned, electric filament lamps pioneered in the late 19th century by Thomas Edison, are a much more sophisticated version of the same idea). All the light a candle makes comes from a chemical reaction known as combustion in which the wax (made from carbon-based chemicals typically derived from petroleum) reacts with oxygen in the air to make a colorless gas called carbon dioxide.
Water is also produced in the form of steam. Since the wax never burns perfectly cleanly, there’s also a little smoke produced. The smoke is an aerosol (tiny particles of solid, unburned carbon from the wax mixed in with the steam) and it often leaves a black, carbon deposit on nearby walls or the ceiling above where the candle’s burning.
The steam is made in the blue part of a candle flame, where the wax burns cleanly with lots of oxygen; the smoke is made in the bright, yellow part of the flame, where there isn’t enough oxygen for perfect combustion to take place.