A candle looks simple and even mundane but look closer and you will see that it’s a classic example of ingenious technology. Set fire to the wick and heat rapidly travels down into the wax body of the candle. Because the wax has a very low melting point it turns into a hot liquid and vaporizes, funneling straight up around the wick as though it is rushing into an invisible smokestack (chimney). The hot wax catches light and burns, creating the flame you see. Most of the light energy is given off as radiant heat, but some of it also gives off heat by chemiluminescence (light emitted from chemical reactions).
The hottest part of the flame is actually the dull blue area to one side of the flaming tip. This is because it is undergoing combustion and releasing three quarters of its energy as heat and only a quarter of its energy as light.
The rest of the flame is a yellow/white luminous zone that rises up from the dark zone. It is the brightest portion of the flame and it also contains unburned carbon particles which emit soot. This is where the flame sputters and flickers. This is usually a sign that the combustion process has not yet stabilized and can be caused by a poorly trimmed wick. Once the combustion process is stable the flame will burn more consistently.