The atomic emission spectrum of an element is the set of frequencies of the electromagnetic waves emitted by atoms of that element. Each atom's atomic emission spectrum is unique and can be used to determine if that element is part of an unknown compound.
The emission spectrum characteristics of some elements are plainly visible to the naked eye when these elements are heated. For example, when platinum wire is dipped into a strontium nitrate solution and then inserted into a flame, the strontium atoms emit a red color. Similarly, when copper is inserted into a flame, the flame becomes light blue. These definite characteristics allow elements to be identified by their atomic emission spectrum. Not all lights emitted by the spectrum are viewable to the naked eye, it also includes ultra violet rays and infra red lighting