The overhead projector is a device with a large lens on top of a metal box containing a bright lamp. It projects the light through a mirror and lens onto a screen, allowing transparencies to be easily created, presented in sequence, and reused for both large and small groups. First used for police identification in 1945, overhead projectors became a popular academic tool in the late 1950s due to providing a bright, clear image even in bright rooms while allowing the teacher to face students and maintain eye contact during discussions.

1. Overhead Projector
Device having a metal box with a large lens as
its top, a bright lamp inside and an arm
protruding upward from the box
A mirror and lens, housed in the head at the
end of that arm focus the light from the
base and direct it forward onto a screen

2. Transparencies writing.
Easy to prepare
Sequenced presentations.
Reusable.
Can be used with both large and small groups.

3. First projector being used for police
identification purposes in 1945
By the late 1950s, overhead projectors had
become a popular academic tool

4. Gives a bright image on the screen
Image is clear even in a bright room
The transparencies are easily carried
around and stored

5. Can face audience while discussing
The teacher can maintain eye contact
Transparencies can be made professionally
or by the teacher

6. Discussing information on the
transparency
Can prepare transparencies ahead of time or
write on them during presentation
The transparencies are easily carried
around and stored

7. Disadvantages
Costs money, especially if each classroom is
to have one
Moving the projector around can result in
damage
Transparencies become overheated
The process of getting the projection image at
a height where all can see often produces a
"key stoning" effect

8. A slide projector is a specialized projector
which has been designed to be used with
slides.