What Color Is the Hottest Flame?

A blue flame is a result of complete combustion, where the fuel is burned efficiently with a sufficient supply of oxygen. This type of flame is hotter than a flame that is yellow or orange, which indicates incomplete combustion. A Bunsen burner, for example, produces a pale blue flame when its air and gas mixture is optimal, reaching temperatures of about 1,500 °C (2,700 °F). This blue flame, just above the tip of the primary flame, is the hottest part of the Bunsen flame.

The color of a flame corresponds to its temperature. As the temperature of a flame increases, we perceive its color changing from red to orange, yellow, and then blue (or bluish-white). This sequence of colors is known as the blackbody radiation sequence, which describes how an object’s peak of radiation energy moves into the visible spectrum as its temperature rises.