Editing Hawthorne effect (section)

== Illumination experiment ==
The illumination experiment was conducted from 1924 to 1927. The purpose was to determine the effect of light variations on worker productivity. The experiment ran in two rooms: the experiment room, in which workers went about their workday under various light levels; and the control room, in which workers did their tasks under normal conditions. The hypothesis was that as the light level was increased in the experiment room, productivity would increase.

However, when the intensity of light was increased in the experiment room, researchers found that productivity had improved in ''both'' rooms. The light level in the experiment room was then decreased, and the results were the same: increased productivity in both rooms. Productivity only began to decrease in the experiment room when the light level was reduced to about the level of moonlight, which made it hard to see.

Ultimately it was concluded that illumination did not have any effect on productivity and that there must have been some other variable causing the observed productivity increases in both rooms. Another phase of experiments was needed to pinpoint the cause.