If you enjoyed a holiday dinner lit by candles then you might be interested to know that the majority of the light from the candle does not come from the combustion of the candle wax in the flame, but from the unburnt soot glowing in the intense heat of the flame. The combustion process generates the heat and the blue colour in the centre of the flame. However, due to the lack of sufficient oxygen, the combustion of the candle wax is incomplete and this produces particles of unburnt carbon. The unburnt carbon forms soot or graphite, but also more exotic structures of carbon atoms, such as nano-diamonds. The average candle has been estimated to produce about 1.5 million nano-diamonds per seconds, or maybe 10 billion nano-diamonds per Christmas dinner! Unfortunately, they are too small to see otherwise they would add a lot of sparkles to festive occasions.
The picture is an infrared image of a 1cm diameter candle. About 2cm of the candle height extends from the bottom of the picture and the visible flame is about 2cm high.
Helen Czerski, Storm in a Teacup: The Physics of Everyday Life, London: Penguin Random House, 2016.