What is a Projection Television?

Projection television refers to a television system that uses an optoelectronic system to project the image on the screen of a television picture tube onto a larger special screen. The picture size of a projection television can be enlarged as needed. ^[1]

Projection televisions appeared in the early 1970s, and sales have increased since the 1990s, with clear improvements in clarity, brightness, and contrast over the past 20 years.

Projection TV is the most widely used of various large-screen TVs. From the perspective of the projection device of the projection television, the projection television mainly has two types: a projection tube type and a liquid crystal type. The projection tube type projection television uses an optical system similar to a magnifying glass to project a television image on a small, high-brightness CRT (cathode ray picture tube) after magnification onto a special screen. This small, high-brightness CRT is called a projection tube. Projection tube-type projection TVs have low brightness and limited image sharpness. To solve this problem, the principle of the film projector is used to make the

(1) According to the display technology, projection televisions are mainly divided into three-tube projection televisions (CRT projection technology), color liquid crystal projection televisions (LCD projection technology) and DLP projection televisions.

(2) Projection TV sets are generally divided into movie projection TV sets, data projection TV sets, and graphic projection TV sets according to use.

(3) Projection televisions are divided into front projection televisions and rear projection televisions according to the projection method.

The front projection television is also called a front projection television. The projection television is separated from the projection screen. The projection television is on the same side as the audience. The projection television projects from the front or rear of the screen.

The rear projection type TV has its projection part enclosed in the case, so the brightness has been greatly improved, and it can be viewed during the day. Its appearance is similar to that of ordinary televisions, eliminating the interference of stray light. ^[3]

Compared with ordinary televisions, projection televisions have the following characteristics:

1. Projection televisions of different screen sizes all use the same size projection tube (7 inches or 9 inches), which is conducive to the formation of projection television product series with different screens.

2. The surface of the projection screen does not form specular reflections and glare. When there are electric lights, windows, or other bright objects around, the surface of the picture tube of an ordinary color TV will form an image or reflect glare, which makes people feel dazzling.

3 Projection TV is an image projected on the diffuse layer of the screen. The light is soft and not dazzling. There is no x-ray radiation on the screen. Watching your eyes for a long time is not easy to fatigue.

4 The projection tube is small in size and has no shadow mask. Little affected by the geomagnetic field.

5. There is a lot of space inside the case, which can be fully utilized to improve the sound design.

6. The projection screen has a certain light gain, about 5-8dB, which improves the image brightness.

7. There is a certain range of viewing angles. As the viewing angle increases, the brightness decreases. The viewing angle where the brightness drops to half, usually the horizontal direction: + 35 ° + 40 °, the vertical direction: ± 10 °. ^[4]

1. Light output

Light output refers to the luminous flux output by the projection television, and the unit is lumens (lm). A physical quantity related to light output is illuminance, which refers to the ratio of the light energy emitted by the screen surface to the screen area when illuminated by light. The commonly used median of illuminance is lux.

2. scanning frequency

The number of horizontal scans per second on the screen by the electron is called the horizontal scan frequency. The horizontal scan frequency of the video projection television is a fixed value of 15625Hz (PAL system) or 15750Hz (NTSC system). The horizontal scanning frequency is an important indicator to distinguish the grade of the projection TV.

The number of vertical scans per second on the screen by the electron is called the vertical scan frequency, also known as the refresh rate, which indicates the number of times that the image is refreshed per second. The vertical scanning frequency is generally not lower than 50Hz, otherwise the image will have a flickering feeling.

3 Video bandwidth

The total bandwidth of the video channel of the projection television is defined as the upper limit frequency of the corresponding signal when the video signal amplitude drops to 0.707 times. Video bandwidth is also an important indicator for projection televisions. To improve image resolution, video bandwidth must be increased.

4 Resolution

The resolutions often given on the technical specifications of projection televisions include addressable resolution, RGB resolution and video resolution.

For CRT projection televisions, the addressable resolution is an important parameter of the quality index of the projection tube. The addressable resolution refers to the highest pixel that the projection tube can distinguish. It is mainly determined by the focusing performance of the projection tube. The addressable resolution should be higher than the RGB resolution.

RGB resolution refers to the highest pixel that a projection TV can reach when connected to an RGB video signal. RGB resolution is related to horizontal scanning frequency, vertical scanning frequency and video bandwidth.

Video resolution refers to the highest resolution of a projection TV when displaying composite video.

5. Contrast

The larger the contrast value, the greater the difference in brightness between the full black and full white images, and the wider the range of grayscale expression.

6. Projection size

Picture size is also an important indicator of a projection television. It is usually expressed by the diagonal length of the projector that can project the largest and smallest pictures on the screen. The unit is inches or centimeters. Projection screen size can be selected according to living environment and audiovisual space. The projection screen size of a household three-tube projection TV is generally 40 ~ 120in, which can be adjusted in a wide range as required. ^[3]