Why don’t flames have shadows? It may seem freaky, but it has to do with what a hydrocarbon flame is. When you look at a candle flame, the part you can see is not a gas or a plasma, but a solid. A flame is a chemical salad full of wax and oxygen molecules that are burning, as well as carbon dioxide, water vapor, hot air, and unburnt solid fuel particles that are so hot they are glowing incandescently, which is where the light comes from. However, all of this stuff is not very crowded; in fact, a flame is about only a quarter as dense as the surrounding air, so light can pass right through. Whatever shadow is created can be easily filled in by the glow of the flame itself. What the flame mainly does to light can be revealed by using a light that is brighter than the flame. Light travels at different speeds through media that have different densities, so passing from the hot flame to the cooler air causes ghostly distortions of intensity, which is the only evidence that anything is there.