INTRODUCTION
the Visual display Unit (VDU) according to International Labour Office (1989) defined VDU as an electrical instrument that is use to display the information recieved from the computer system,in a very short period of time emerged from comparative obscruity in scientific laboratory(s) to become an integral and indespensable part of normal working life for millions of people both in home and in workplaces. As the technological revolutioncontinues, the use of computer with screen-base output unit or VDU grows at an incresing rate. worlwide, millions of VDUs are now in use, recieving and processing information on television-like screen or monitors. Also, it is a television type monitor that display information recieved from computer system wordprocessor rather than from a signal broad cast for televisio. The VDU contributes the interactive element between the operator and the computer system. The VDU could be limited to a main computer, as with a terminal or the physical entity comporising the VDU could also include the computer system, as with a personal computer (PC). the basic principle of operation of most VDUs in use is simikar to that of television sets.They contain a large evacuated glass tube, called Cathode Ray Tube (CRT), which include a source of electrons (The Cathode) and a phospor coating on thte inside of the vewing face of the screen. A high voltage (typically) in the range of 10-25kv accelerated electrons, releasing from the cathod towards a second electrode called The Cathode. They pass the through a hole in the anode on to the phosphor materials. However, computers are very important and for all the apparent complexity, they seems to hve a wide range of uses and play an ever-increasing role within our society likeoffice, commerce and industries, public services and of course schools and home, with this we can see that the importance of computer monitor can not be over emphasis.
