How do the individual forces compare when the rider experiences a sensation being lighter than his normal weight ? What is the acceleration direction when this occurs ?

When the elevator is accelerating downward, the person feels lighter due to the downward normal force being less than the person's weight.

Explanation:

A person riding in an elevator subjected to a series of unbalanced forces depending on the direction the elevator is travelling.

Two forces are acting on the person; the force of gravity and the upward normal force from the elevator.

When the elevator is going upwards with acceleration a, the person feels heavier than his normal weight, due to the upward normal force being greater than the person's weight. N = mg + ma

When the elevator is moving downwards with acceleration a, the person feels lighter due to the downward normal force being less than the person's weight. N = mg - ma

However, when the elevator is moving up or down at constant velocity ie. acceleration a = 0, the person experience a normal force equal to weight. N = mg

When the elevator is moving downwards with acceleration a = g, the person experiences weightlessness. N = (mg - mg) = 0