What did the researchers, who identified the hawthorne effect, see as evidence that employee performance was influenced by something other than the physical work conditions?

The researchers found that the productivity of the more highly illuminated workers increased much more than that of the control group. They also found out that their productivity even improved when the lights were dimmed again. As a result, the researchers concluded that it was not the changes in physical conditions that were affecting the workers' productivity. Rather, it was the fact that someone was actually concerned about their workplace.