The marketing research firm Stealth is conducting a study on…

The marketing research firm Stealth is conducting a study on lighting, and how different levels of light impact consumer purchase behavior in a retail environment. Stealth believes high levels of light increase the amount of money people spend at a retail store. In order to test this relationship, Stealth decides to conduct an experiment. Their goal with the experiment is for the findings to be as generalizable as possible, with strong external validity. Which type of experiment should Stealth run?