Various qualifiers have been added to the term “naphtha” by various sources in an effort to make it more specific:

One source[6] differentiates by boiling point: Light naphtha is the fraction boiling between 30 °C and 90 °C and consists of molecules with 5—6 carbon atoms. Heavy naphtha boils between 90 °C and 200 °C and consists of molecules with 6-12 carbons.

Another source[7] differentiates light and heavy based on hydrocarbon structure: “Light[is] a mixture consisting mainly of straight-chained and cyclic aliphatic hydrocarbons having from five to nine carbon atoms per molecule. Heavy [is] a mixture consisting mainly of straight-chained and cyclic aliphatic hydrocarbons having from seven to nine carbons per molecule.”