When training to build up muscle size, should I use lighter weight in higher reps and sets or use heavier weight in lower reps and sets?
Optimal muscular hypertrophy is achieved by using enough weight that makes you hit failure in the 6-10 rep range. To answer your question frankly, neither. This weight range would be considered moderate. Higher weight would mainly increase strength, while lower weight would mainly increase endurance.
There are two types of training; neural adaptation and hypertrophy. Your pure focus here is hypertrophy training which focuses on the size of the muscle. This means breaking it down, letting it heal and working it out again to repeat the cycle. Proper food and nutrients allows the body to use the proteins/fats/carbohydrates to rebuild the tissue which was broken down. That adds bit by bit size to muscles. There are always tricks like supplementing with arginine causes your blood vessels to expand giving you a more full look or in the extreme case (ILLEGAL) steroids which allows you to rebuild quickly, allowing you to work out the muscle faster and longer opposed.
To effectively break down the muscle you need to put in some work. Start week one with 3 sets of 6-10 reps with a good amount of weight. The following week the exercise will be 4 sets, then 5 then maybe 6. You have to put the work in to overcome stagnation and force the body to shift in the anabolic phase. Eat lots of dense foods to complement a program like this.
Let me put this in a very simple thought process. When you train/workout you put your body under a certain amount of stress. The body's muscle tissue breaks down and searches for ways to recover (food, rest, etc.). In the recovery process the body builds a "shield" of muscle to become accustomed to the level of stress you put your body under. Take a lumberjack for example (very strongly build, powerful individual)...he constantly is moving heavy pieces of lumber. His body's reaction is to build layers of muscle/mass to cope with the stress. That's why the more work you put into something the better the result. That's basically what training really is. Putting the work in and allowing your body to adapt to the stress. That is why you constantly need to shock the body to break through plateaus...