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Name: Brent
Status: student
Grade: 9-12
Location: TN
Country: N/A
Date: September 2006

Why does a luminous flame appear yellow and a nonluminous flame appear blue?

The yellow color in a luminous flame is basically the black-body emission from hot particles of soot in the flame. they are hot, and they glow like the filament of a light bulb.

In a blue flame, there are no particles of soot to give that incandescent radiation. Instead, the main color you see is blue emission from the high-energy C2 molecule.

Richard Barrans


The frequency or wavelength of light released by atoms or molecules depend on the energy being released by those substances. The Planck Equation describes exactly that, that there is a specific energy to a specific wavelength or frequency.

The difference between a yellow and blue flame depend on the amount of oxygen that is mixed in with the fuel. More oxygen means that the combustion reaction is more efficient and more energy is released. Remember that the more blue the visible light appears, the more energy that light will have.

Thus, it should make sense now that when more oxygen is fed into the system, the combustion is more efficient, more energy is released, and the light will be on the more energetic end of the spectrum, blue.

Greg (Roberto Gregorius)

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