How does a T.V set show different different colours if the fluorescence in the cathode tube is always green?

Question

Our professor at college told us that irrespective of the gas used in the cathode ray tube ,it generates only green colour as fluorescence then how come the T.V sets show colours other than green although it uses the cathode tube?

Answer 1

You definitely need a new college professor ! Firstly there is no gas inside a CRT they are evacuated to a very hard vacuum . There are three guns which when all are turned on will illuminate the groups of three phosphor dots that the CRT face plate is coated with , all guns = white , the different colours are obtained by switching the guns on and off to produce differing colours, for instance if the blue gun is turned off then only the red and green dots are illuminated and you have a yellow screen ! of course if only the blue gun fires then you have a blue screen, from that you should be able to see how all the colours can be had by switching the guns on and off or varying the intensity of the guns to produce any colour you want .! There is a lot more that could be said but it is not practical to write a book on the subject on Yah answers ! PS Get rid of the prof he obviously has no clue whatever !!!

Answer 2

By adjusting the three guns of the CRT to achieve a color balance of White. This is done by collapsing the Vertical to a narrow line in the center of the screen. The gun can then be adjusted to achieve a white line. The guns are now balanced and will produce the correct colors when the electron beams strike the Phosphor Dot coating on the inside of the screen.

These adjustments are also done with test equipment, but an experienced Tech can do it accuratly with the visual adjustment.

Answer 3

realist 2006 is correct. The three guns are slightly offset from each other and they fire an electron beam through holes in a 'shadow mask' located just behind the face of the CRT. this offset allows each of the three guns to strike a different place on the face and each finds it's own color of phosphor. Put a magnify glass to the front of your TV screen. The CRTs now are all in-line (offset), red green and blue are rectangles and are next to each other. But if you get a chance you should see the old delta (offset) CRTs, red green and blue are circles in a triangle pattern.