Overhead Projectors Key Terms

Display your expertise with overhead projector key terms

Many companies and organizations use overhead projectors during meetings and presentations in order to display information for a viewing audience. The audience may consist of students, board members, employees or even potential clients. An overhead projector must function when you need it, where you need it. To fully understand the machine, you should know key terms for its parts, as well as for light sources. 

Fresnel Lens

A Fresnel lens controls the refraction of light. The lens is flat in nature and is made up of close grooves. This lens is typically part of the stage part of the overhead projector where material is placed for projection onto the screen.


Lumens are the unit used to measure the brightness of an overhead projector. The more lumens that a projector has, the brighter the light. The word comes from the Latin word "lumen," which means light.

Triplet lens

A triplet lens is a lens in an overhead projector that has three parts all in one assembly piece, as opposed to a convex lens. The lens helps focus the image on the screen.


Keystoning, in terms of overhead projectors, takes place when there is distortion of the displayed image. The distortion is caused when the image is not perpendicular to the screen on which it is displayed. Keystoning is often corrected by tilting the screen.

Luminous efficacy

The luminous efficacy is calculated by dividing the total luminous flux from a light source by the input given by the lamp. This total is measured in lumens. When expressed as a percentage, it is often called luminous efficiency.


The term lamp in an overhead projector describes the light source. A lamp is a small lightbulb that creates the light which the lens uses to display the image.

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