Philips LP2PB201CS - Manual (Page 28)

How displays create colors
A color display, being a CRT based device, acts itself as a light source and the way
how it creates colors is based on the aforesaid Additive principle.
The inside surface of the CRT screen is coated with three special type of phosphors
that, when struck by high energy electrons, glow with particular frequencies of light
perceived respectively as the Red, Green and Blue primary colors.
The phosphors are arranged in groups of 3, called triads, with each phosphor being
driven by one of the three RGB guns. A perforate metal shield known as shadow
mask acts as a filter to separate the three electron beams so that they can strike the
designated phosphors only.
As the three electron beams scan each video line, they pass in turn through each
slot in the shadow mask and impinge on their respective phosphor in the associa­
ted triad.
The perceived color is thus a combination of the three primary colors depending on
the relative magnitude of the three RGB beam currents; if all the guns fire at full
intensity then white light is perceived; if just one gun hits its corresponding phosphor
then a single color is perceived; if none of the dots are hit the triad remains biack.
The combination of these glowing phosphors, addressed by the video input signal
coming from your computer, creates the color images you see on the screen.
About color uniformity
Because of traditional limitations in CRT technology, most large screen color moni­
tors show uneven brightness over the total screen area.
For example, the fact itself that CRT glass thickness is increased at the screen cor­
ners to improve mechanical resistance or a non uniformity in shadow mask hole
sizes will cause a lack of brightness in these areas, while a non uniformity in pho­
sphors displacement or sensitivity will show some areas where color characteristics
are different from others.
When some areas of the screen are brighter or show different colors than others,
then image quality decreases and ‘real life’ images reproduction cannot be granted
anymore, especially when the monitor is used for creating color artworks electroni­
cally.
Appendix A
21