Projection clock
Encyclopedia
A projection clock is an analog
Analog signal
An analog or analogue signal is any continuous signal for which the time varying feature of the signal is a representation of some other time varying quantity, i.e., analogous to another time varying signal. It differs from a digital signal in terms of small fluctuations in the signal which are...

 or digital clock
Digital clock
A digital clock is a type of clock that displays the time digitally, i.e. in cyphers, as opposed to an analog clock, where the time is displayed by hands. Digital clocks are often associated with electronic drives, but the "digital" description refers only to the display, not to the drive mechanism...

 equipped with a projector
Image projector
An image projector is an optical device that projects an image onto a surface, commonly a projection screen.Most projectors creates an image by shining a light through a small transparent image, but some newer types of projectors can project the image directly, by using lasers...

 that creates an enlarged image of the clock face on any suitable projection screen
Projection screen
A projection screen is an installation consisting of a surface and a support structure used for displaying a projected image for the view of an audience. Projection screens may be permanently installed, as in a movie theater; painted on the wall; or semi-permanent or mobile, as in a conference room...

, most often the ceiling. They are not very complex, and can be built by hobbyists.

The advantage of a projection clock is that the "clock" can be placed almost anywhere, even on surfaces difficult to install traditional clocks on. They can also be moved easily, and depending on the projector used, the image can be in monochrome
Monochrome
Monochrome describes paintings, drawings, design, or photographs in one color or shades of one color. A monochromatic object or image has colors in shades of limited colors or hues. Images using only shades of grey are called grayscale or black-and-white...

 or color. The image generated by most projection clocks is large enough that a nearsighted person can see with it from a distance without glasses or contact lenses, while an ordinary clock of similar size would be costly and impractical.

Projection clocks are also used in advertising
Advertising
Advertising is a form of communication used to persuade an audience to take some action with respect to products, ideas, or services. Most commonly, the desired result is to drive consumer behavior with respect to a commercial offering, although political and ideological advertising is also common...

 and merchandising
Merchandising
Merchandising is the methods, practices, and operations used to promote and sustain certain categories of commercial activity. In the broadest sense, merchandising is any practice which contributes to the sale of products to a retail consumer...

. High-brightness analog projection clocks can superimpose a business' logo on top of the clock face, while there are low-brightness projection clocks designed for Ferrari
Ferrari
Ferrari S.p.A. is an Italian sports car manufacturer based in Maranello, Italy. Founded by Enzo Ferrari in 1929, as Scuderia Ferrari, the company sponsored drivers and manufactured race cars before moving into production of street-legal vehicles as Ferrari S.p.A. in 1947...

 fans that project a Ferrari logo in addition to the time.

Most of the projection clocks on the market today are connected to the Atomic U.S. Time That means that the clocks will always provide an accurate time as they sync with the U.S. Atomic Clock
Atomic clock
An atomic clock is a clock that uses an electronic transition frequency in the microwave, optical, or ultraviolet region of the electromagnetic spectrum of atoms as a frequency standard for its timekeeping element...

.

History

Projection clocks were patented at least twice: once in 1909, and another time in 1940 http://www.roger-russell.com/project/project.htm. Both patents have expired by now, so any company or hobbyist can build projection clocks.

Previously, projection clocks, like other clocks of that period, were universally analog. With the widespread adoption of digital clocks, digital projection clocks have also appeared.

Technology

A projection clock usually needs a backlight, as most clock displays do not radiate their own light. The backlight can use different lighting technologies, from incandescent bulbs
Incandescent light bulb
The incandescent light bulb, incandescent lamp or incandescent light globe makes light by heating a metal filament wire to a high temperature until it glows. The hot filament is protected from air by a glass bulb that is filled with inert gas or evacuated. In a halogen lamp, a chemical process...

 to LEDs
Light-emitting diode
A light-emitting diode is a semiconductor light source. LEDs are used as indicator lamps in many devices and are increasingly used for other lighting...

.

Projection clocks can be divided into two groups: low-brightness and high-brightness. The image created by low-brightness projection clocks can be viewed only in a darkened room, while high-brightness ones create an image that can be viewed even in lighted rooms, but are more power-hungry.

Low-brightness projection clocks

Most modern projection clocks use a red LED-based projector, and also an ordinary LED or 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....

 display. That is convenient, since these clocks are low-brightness, and the conventional display can be read when the room is not darkened and the image generated by projector is unreadable. Such projection clocks are often integrated into clock radios and home weather stations. Clock radios equipped with projectors are only slightly more expensive.

High-brightness projection clocks

Modern high-brightness projection clocks are in most cases analog, and have a halogen bulb backlight. In most cases they use a set of rotating and fixed transparent discs with hands and a face. Sometimes, an LCD is integrated into this set to combine analog and digital information on the projected image. They are more expensive than low-brightness ones.

Projectors used in projection clocks are similar to other projectors, and use the same optical principles. Most of them use lenses
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...

, but some use the principle of shadow theater, vector scanning or raster scanning
Raster scan
A raster scan, or raster scanning, is the rectangular pattern of image capture and reconstruction in television. By analogy, the term is used for raster graphics, the pattern of image storage and transmission used in most computer bitmap image systems...

.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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