Question

What makes the middle zone of a candle flame luminous (or light-giving)?

Answer 1

A candle flame is formed because wax vaporizes on burning. ... The innermost zone, directly above the wick, contain wax that has been vaporized but that is unburnt. It is the darkest zone. The middle zone is yellow and luminous because As it is an oxygen-depleted zone, insufficient oxygen exists to burn all of the wax vapor. As such, partial combustion of wax takes place. The zone also contains unburnt carbon vapor. The temperature in this region is hotter than the innermost zone but cooler than the outer zone. The outer zone is the area where the flame is the hottest and complete combustion of wax takes place. It is light blue in color and not normally visible.