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In overhead projection, the picture is projected over the head of the speaker on the screen. This is accomplished by an overhead projector. Drawing, diagram, lettering etc. are made on transparent sheets and are put on the glass platform of the overhead projector, through which strong light is passed. The rays of light are converged by a lens and reflected by a mirror held at an angle, on the screen at the back.
The instructional items may be written or drawn by hand on transparent sheets, transparent cellophane or polythene rolls with a special pen or wax crayon. These may be wiped cleaned with a dry cloth. Printing on transparencies may be made through photographic, Xerox or electric processes. The transparencies may be in colour or in black and white, and may be repeatedly used.
Overhead projection enables the speaker to simultaneously deliver the talk and project the instructional materials, while facing the audience. The speaker can also write, make sketch and ease while projecting them. Important psychological techniques like covering a portion of the transparency with a sheet of paper and making progressive disclosure and superimposing diagrams may be achieved in overhead projection at ease and in an effective way. A thin object may be placed on the transparency and used as pointer by the speaker. Overhead projection is used in training programmes, group meetings, seminars, symposium, workshop etc.
Advantages:
- Makes the talk dynamic and sustains audience interest
- Complex ideas may be clearly presented
- Saves time in presenting the talk
- Projection of pictures may be synchronized with the talk
- Enables the speaker to face the audience and observe their reaction
- Enables the audience to take notes
- Easy to prepare and project the instructional material
- Materials for transparencies are cheap and easily available
Limitations:
- Requires good preparation by the speaker
- The overhead projector is a bit costly equipment
- Instructor must be close to the projector to change the visual
- There is a tendency to sit down and instruct which can dampen the enthusiasm of learners
- Effectiveness, heavily depends on the presenter
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