If you intend TRAINING there is NO SUCH THING BY DEFINITION AS LIGHT WEIGHTS!!
Firstly some definitions.
Training ; movement that has a defined end purpose and specific physiological goal.
Exercise ; Moving for enjoyment using primarily the muscular and cardiovascular system for loosely defined purpose and physical improvement.
Rehabilitation ; The act of restoring the body to it’s original state following trauma, injury or illness.
Weight you move is defined by several goals.
1. Technique – If the weight compromises the required technique or purpose the load is mechanically too heavy.
2. Intent – What you intend doing with the weight defines the load. Are you under tension or simply under load?
3. Cumulative repetitions – If your goal is 4×15 your intention is to move 60 repetitions cumulatively. If the weight is too heavy in the first set or challenging, the drop off curve (Number of reps in every proceeding set) will compromise the actual goal (60 reps).
At all stages in working sets there are no situations with the exception of rehabilitation that you use LIGHT WEIGHTS.
You use the heaviest weight you can at all times whilst staying within the purpose and goal of the session.
WEIGHT on the bar or machine is defined largely by repetitions.
Too many people think they’re doing light weights and high reps when they are simply doing high reps THAT is what defines the weight.
(Another reason that miss Anderson gives out some of the worst advice on the fitness planet)