الشاشة الفوسفورية المضيئة .. كتاب التلفزيون الملون والعادي

2-11 (1) The luminous phosphorescent screen:

It is the front face of the image diode on which the TV scenes appear. It is made of thick transparent glass coated from the inside with a phosphorescent material in the form of dots that glow in one of the three colors - red - green - blue when the electronic beam from one of the three launchers hits them. Each ray is concerned with one of the three primary colors
(11 - 2) - (11 - 3).

The phosphorescent points are placed so that every three points of different color form an equilateral triangle, and it is called the DELTA method (Fig. 11 - 4 - B) and the number of phosphorous dots reaches (400,000 triple groups) - and they are close together so that the distance between the triples does not exceed (1.7 mm) in the screen measuring (25 inches). The distance is less on smaller screens - so that the eye does not distinguish these small voids, so the image appears as a merged and integrated unit - but one of the difficulties facing the appearance of an image with good lighting and contrast is the loss of a large part of the lighting energy of the phosphorescent granules on the inner surface of the screen. As 50% of the light is reflected into the screen to no avail. And 20% of the light is lost inside the glass of the screen, so only 30% of the light generated by the image-forming beam reaches the viewer. The shadow mask also prevents a section of the electrons from reaching the screen.

Among the factors affecting image clarity and contrast are:

1- A light halo forms around each bright point. 2- The curvature and curvature of the screen surface, which increases the loss of contrast

3 - Reflection of light from the surface of the screen to the inside (Fig. (6-11).
4- The reflection from inside the screen, and its effect is reduced by coating the inner wall of the screen with a black layer that also has electrical benefits.

​​​​​​The technology of manufacturing screen valves has advanced, which has greatly improved its performance. Among these improvements is wrapping the luminous phosphorescent layer with a thin layer of aluminum, which prevents the light from returning and reflecting inside the LED (Fig. The color image does not have the same light yield, so forming a white color requires that the anode current be around 34% for the red color, 38% for the green color, and 28% for the blue color (refer to Chapter Two of the book). device, and perform the final adjustment process for it - called the process of adjusting the whiteness