2 2: 4 3: 6 e 4: ge 5: Dollars per unit 12 = 9 8 100 125 150 200 300 Quantity of energy-efficient light bulbs (thousands) B FIGURE 3-1 10 D Refer to Figure 3-1. The movement along the demand curve. D. from point v to point x, could be caused by a change in the price of energy-efficient light bulbs. an increase in household income, which allows consumers to purchase more light bulbs.. a change in the price of ordinary light bulbs.