A transparency, also known in industrial settings as a "viewfoil" or "foil", is a thin sheet of transparent flexible material, typically cellulose acetate

Cellulose acetate

Cellulose acetate , first prepared in 1865, is the acetate ester of cellulose. Cellulose acetate is used as a film base in photography, as a component in some adhesives, and as a frame material for eyeglasses; it is also used as a synthetic fiber and in the manufacture of cigarette filters and...

, onto which figures can be drawn. These are then placed on an overhead projector

Overhead projector

An overhead projector is a variant of slide projector that is used to display images to an audience.-Mechanism:An overhead projector typically consists of a large box containing a very bright lamp and a fan to cool it. On top of the box is a large fresnel lens that collimates the light...

 for display to an audience. Many companies and small organizations use a system of projectors and transparencies in meetings and other groupings of people, though this system is being largely replaced by LCD projector

LCD projector

An LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surface. It is a modern equivalent of the slide projector or overhead projector...

s and interactive whiteboards.

Creation of transparencies

Transparencies can be created in one of two ways.

First, a laser printer

Laser printer

A laser printer is a common type of computer printer that rapidly produces high quality text and graphics on plain paper. As with digital photocopiers and multifunction printers , laser printers employ a xerographic printing process, but differ from analog photocopiers in that the image is produced...

 can be connected to a computer, which is loaded with a cartridge of celulose acetate sheets. An image or document is then created within the computer

Computer

A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...

, though images are prevalent due to text being illegible at certain distances f rom a projection, and then formatted to be printed. From there, the printer is engaged and the document printed onto the sheet of acetate. Some people prefer to test the transparency before sending it out to the person requesting it.

Secondly, some black and white or color copiers are able to print onto, or can be configured to handle, acetate sheets. These are usually toner-based copying machines, as inkjet-based technology is not yet capable of printing on acetate sheets. A person may place a document or a book on the surface of the copying machine and make one or several copies onto acetate, if there are simultaneous meetings or if another company or organization wants a copy.

Uses for transparencies

Uses for transparencies are as varied as the organizations that use them.

Certain classes, such as those associated with Mathematics

Mathematics

Mathematics is the study of quantity, space, structure, and change. Mathematicians seek out patterns and formulate new conjectures. Mathematicians resolve the truth or falsity of conjectures by mathematical proofs, which are arguments sufficient to convince other mathematicians of their validity...

 or History

History

History is the discovery, collection, organization, and presentation of information about past events. History can also mean the period of time after writing was invented. Scholars who write about history are called historians...

, used transparencies to illustrate a point or problem. Math classes in particular use a roll of acetate to illustrate sufficiently long problems and to create illustrations a computer cannot, due to a lack of math symbols on a standard computer keyboard. This problem is typically limited to High School

High school

High school is a term used in parts of the English speaking world to describe institutions which provide all or part of secondary education. The term is often incorporated into the name of such institutions....

 and College

College

A college is an educational institution or a constituent part of an educational institution. Usage varies in English-speaking nations...

-level mathematics, because of the inclusion of Algebra

Algebra

Algebra is the branch of mathematics concerning the study of the rules of operations and relations, and the constructions and concepts arising from them, including terms, polynomials, equations and algebraic structures...

 and Calculus

Calculus

Calculus is a branch of mathematics focused on limits, functions, derivatives, integrals, and infinite series. This subject constitutes a major part of modern mathematics education. It has two major branches, differential calculus and integral calculus, which are related by the fundamental theorem...

 courses, respectively. In recent years, more and more colleges are switching to digital projectors and Powerpoint presentations.

Aerospace companies, like Boeing

Boeing

The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...

 and Beechcraft

Beechcraft

Beechcraft is an American manufacturer of general aviation and military aircraft, ranging from light single engine aircraft to business jets and light military transports. Previously a division of Raytheon, it has been a brand of Hawker Beechcraft since 2006....

, used transparencies for years in management meetings in order to brief engineers and relevant personnel about new aircraft designs and changes to existing designs, as well as bring up illustrated problems.

More tech-friendly churches and other religious organizations used them to show sermon outlines and illustrate certain topics such as Old Testament

Old Testament

The Old Testament, of which Christians hold different views, is a Christian term for the religious writings of ancient Israel held sacred and inspired by Christians which overlaps with the 24-book canon of the Masoretic Text of Judaism...

 battles and Jewish artifacts during worship services, as well as outline business meetings.

Spatial light modulators (SLMs)

Many overhead projector

Overhead projector

An overhead projector is a variant of slide projector that is used to display images to an audience.-Mechanism:An overhead projector typically consists of a large box containing a very bright lamp and a fan to cool it. On top of the box is a large fresnel lens that collimates the light...

s are used with a flat panel LCD

Liquid crystal display

A liquid crystal display is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals . LCs do not emit light directly....

 which, when used this way is referred to as a spatial light modulator

Spatial light modulator

A spatial light modulator is an object that imposes some form of spatially-varying modulation on a beam of light. A simple example is an overhead projector transparency. Usually when the phrase SLM is used, it means that the transparency can be controlled by a computer. In the 1980s, large SLMs...

 or SLM. Data projectors are often based on some form of SLM in a projection path. An LCD is a transmissive SLM, whereas other technologies such as Texas Instrument's DLP are reflective SLMs. Not all projectors use SLMs (e.g., some use devices that produce their own light rather than function as transparencies). An example of non-SLM system are OLEDs

Organic light-emitting diode

An OLED is a light-emitting diode in which the emissive electroluminescent layer is a film of organic compounds which emit light in response to an electric current. This layer of organic semiconductor material is situated between two electrodes...

.