DrFowler Is Interested in Studying How Indoor Lighting Can Influence

Dr.Fowler is interested in studying how indoor lighting can influence people's moods during the winter.A sample of 100 households is selected.Fifty of the homes are randomly assigned to the bright-light condition where Dr.Fowler replaces all the lights with 100-watt bulbs.In the other 50 houses,all the lights are changed to 60-watt bulbs.After two months,Dr.Fowler measures the level of depression for the people living in the houses.In this study,the independent variable is the ____.

A) ​brightness of the lights
B) ​level of depression
C) houses with 100-watt bulbs
D) ​houses with 60-watt bulbs