What is a resistance training method that involves performing a set with light load followed by increasing the load and decreasing the repetitions with each continuing set?

Pyramid system

Explanation:

A pyramid system resistance training is a collection of sets of the same exercise, that start with light weights and higher repetitions, building up to heavier weights and fewer repetitions.

A full pyramid training is an extension of the above mentioned statement, reducing the weight after you have reached the peak until you complete the pyramid.