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Background information 35
APPENDIX A:
BACKGROUND INFORMATION
Luminance Uniformity Correction
A characteristic (or limitation) of every picture tube (CRT) is that the
luminance decreases towards the edge of the screen surface. The
decrease is normally 20 to 30 %.
This is caused by the shape of the picture tube. Inside the CRT, a so-
called electron gun shoots an electron beam towards the front (the
glass panel). Because this panel is rather flat instead of having a
spheric shape, the electron beam has to 'travel' a longer distance in
the corners than in the center. So the intensity is higher in the center.
This phenomenon is even increased by the irregular distribution of the
phosphor and aluminium layer on the glass panel. These tend to be
thicker in the center.
BARCO has developed a special system, called Luminance
Uniformity Correction (LUC), that solves this problem. The LUC
system enhances the light output at the edges of the CRT, so that the
luminance there is the same as in the center.
The LUC system is calibrated in the factory. From time to time, it has
to be re-calibrated at the customer's site by means of the light sensor
you use for normal color calibration. The system can be calibrated
and switched on or off by a qualified technician.
Power saving system
The display is equipped with circuits that can handle power saving
management. When the system is switched on, it can power down the
display in several steps.
The system is controlled by the imaging board or the PC that delivers
the video signals. When you are working on the computer, the
imaging board delivers both sync signals, and the display is operating
normally. When you don't touch the computer keyboard for a certain
time, the imaging board only delivers vertical sync. This is sensed by
the display's micro controller, that blanks the image on the CRT. This
results in a drop of power consumption with about 25 %.
When you leave the computer idle for a longer period, the imaging
board now delivers horizontal sync only. As a result, the display's
micro controller switches off a number of internal circuits. The power
consumption has now dropped with about 42 %.