During training what is best to use heavy or light weight?
Inside the gym I attend the focus is to use light weight for safety. Light means small and heavy means big. That definition is used no matter how many repetitions peoples can do.
Example, ones test me in leg press I did nearly 30 repetitions. So, he set the same weight for 3 set of 15 repetitions.

How light and heavy are determined? What should we use, heavy or light weights, at gym?