What is dark zone, luminous zone and non - luminous zone?

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Solution

Dark zone:

This zone is the outermost layer of the flame. It is the part of flame occurring around the wick of the candle. It mostly contains all the unburnt wax. So when the candle is lit up the unburnt vapours move away upward from the wick. These vapours are combined to form the Dark zone of the flame. So the movement of molten wax up away from the wick is due to phenomenon called capillary action. This molten wax around the wick forms the dark zone. This dark zone is supposed to be the hottest due to the decomposed carbon particles formed during vaporization. Hence the name Dark zone. The flame in this zone appears dark yellowish reddish colour.

Luminous zone:

The zone occurring after the non-luminous zone is the luminous zone. It is a region where incomplete combustion takes place. And a large amount of heat is generated. All the unvapourised gases and the molten wax will be burnt in this zone. There will be vigorous burning action taking place. So the molten wax further vaporises in the existence of vapor particles and wax. The flame is yellowish in colour.
Non-luminous zone:

In the non-luminous zone of candle there will be complete combustion of vaporised gases and the molten wax as there is ample presence of oxygen which aids in combustion. In this region we can observe that there will be a kind of ‘aura’ formed around the candle. As there is complete combustion this region will have lot of heat released.

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