TR Mahalingam can sustain a high pitch for a long time. In Carnatic music, the vocalist can run the show without even any accompaniments. This may not be possible in light music, which has to be supported by the necessary instruments which go well with the tune. The Carnatic system has a history of its own, and is based on a particular pattern, whether it is in scales or the beat. But nobody can define when exactly light music came in.
Traditional music has a great identity.
Light music, in fact, is based on Carnatic music. There cannot be a single tune which is not based on a particular scale. However, light music can be a combination of any systems of music. Nowadays, most of the time, light music is neither Carnatic nor western. It consists of a mixture of any ragas and the systems in it.