A related hypothesis involves the natural chemiluminescence of phosphine. In 2008, the Italian chemists Luigi Garlaschelli and Paolo Boschetti attempted to recreate Mills' experiments. They successfully created a faint cool light by mixing phosphine with air and nitrogen. Though the glow was still greenish in color, Garlaschelli and Boschetti noted that under low-light conditions, the human eye cannot easily distinguish between colors. Furthermore, by adjusting the concentrations of the gases and the environmental conditions (temperature, humidity, etc.), it was possible to eliminate the smoke and smell, or at least render it to undetectable levels. Garlaschelli and Boschetti also agreed with Mills that cold flames may also be a plausible explanation for other instances of ignis fatuus.