Who Invented the Overhead Projector?

Who invented the overhead projector? Although the device appears in nearly every classroom and conference center, few people know much about it. Just as most technological advances capitalize on prior discoveries, so did the overhead projector. Thanks to a company that encouraged employees to invent and experiment, the overhead projector emerged as a crucial component in mainstream teaching technology. Today, more modern developments allow ceiling projectors equipped with LCD technology to bring projectors into the most high-tech boardrooms and classrooms.

Early Versions
The first technology to project an image using light was the opaque projector, the direct ancestor of the overhead projector. In the late 1800s, these devices were used in lecture halls at major universities and also for amusement. At the beginning of the 20th century, the episcope and the epidiascope were two versions of this technology. The episcope projected opaque images, while the epidiascope could project opaque and transparent images. Both relied on a setup of mirrors and prisms to reflect the light and throw it onto a viewer.

Mid-20th Century
The original overhead projectors of the 1940s capitalized on the slide projector technology that had been in use for nearly a century. The elements of a slide projector are the light source, a reflector, a lens that condenses and refocuses the light and another lens for focusing. The US army utilized a version of the overhead projector for war training in the 1940s, and the rudimentary technology would be slowly incorporated into schools and companies in the 1950s and 1960s.

Roger Appledorn
In the 1960s, a young engineer named Roger Appledorn worked at 3M, where employees were encouraged to experiment with new inventions. In a corporation that celebrated new ideas and accomplishments, Appledorn was encouraged to develop a new idea he had about thermographic imaging. He developed a machine that would project writing on clear film onto a flat surface. The company was so excited about the idea that they created the 3M overhead projector line, but there was little initial success. Appledorn and his team boosted marketing efforts by personally calling and visiting with school teachers in order to push the product. The efforts paid off and with the endorsements creating more demand for the "new chalkboard," overhead projectors were on the fast track to meeting all production deadlines and expanding in the market. The company also developed projector screens that optimized viewing of the visuals.