Some of mankind's most remarkable scientific discoveries came to light as a result of research that had nothing to do with the breakthrough itself. And such was the case with quantum mechanics. Back in the early 1890s the German Bureau of Standards asked Max Planck to design a lightbulb that produced the maximum amount of light with the minimal amount of energy. And his research into saving the bureau a few dollars on its energy bills led to the study of quantum mechanics which could one day let us unlock the secrets of the universe.
Oh, and FYI, it turns out that a lightbulb running at 3,200 kelvin gives out the maximum amount of light that is visible by humans, if you're interested in saving a few more dollars and building your own. [YouTube]