Projector Clock
A projection clock is also known as a ceiling clock. This is basically an analog or digital clock equipped with an inbuilt projector that creates an enlarged image of face of the clock on any suitable projection surface or screen, which is invariably the ceiling of a room. These are not very complex and can be built by hobbyists.
Advantages of projection clocks
The advantage of a projection clock is that it can be installed anywhere, even surfaces difficult to install conventional clocks on. They can also be moved easily depending on the projector used. The image projected can be in monochrome or color. The image generated by most projection clocks is large enough for a nearsighted person to easily see from a distance. An ordinary clock of similar size of the projected image would be expensive and impractical.
Projection clocks are also used in advertising. High-brightness analog projection clocks can be used to superimpose a business logo on the clock face, while there are low-brightness projection clocks designed for sports fans to project a favorite sports star or logo in addition to the time. Projection clocks, like other clocks of the analog period, were generally analog. With the widespread adoption of digital clocks, digital projection clocks seem to have become the popular choice for many.
How it works
A projection clock, almost in all cases needs some form of a backlight. Clock displays do not radiate their own light. Different lighting technologies can be used to generate luminance to facilitate the projection of the face of the clock on to a screen or surface. These techniques can range from incandescent bulbs to LEDs. Projection clocks are divided into two groups, low-brightness and high-brightness projection clocks. 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 consume much more power.
Precautions
Most projection clocks draw their power from the mains of the house. Some also use other potentially dangerous technologies such as halogen bulbs and lasers. Halogen bulbs produce very high degrees of heat and can cause fires if not kept away from incandescent materials and can even explode if exposed suddenly to cold air. Lasers one the other hand can cause blindness id directed into the naked eye. So care should be observed when dealing with high power projection clocks.