Laser Printer and Photocopier - What is the Difference?
Laser printers and photocopiers both make use of the process known as Xerography:
“a dry copying process in which powder adheres to parts of a surface remaining electrically charged after being exposed to light from an image of the document to be copied” (Oxford English Dictionary).
However, there are 2 significant differences in the way the process is implemented.
How Laser Printers 'v' Photocopier Source the Image
• Laser printers do not scan a document prior to forming any image on the photoreceptor. They start by receiving the document data in a digital format.
How Laser Printers 'v' Photocopier Produce an Electrostatic Image on the Drum
Initial State of the Drum
The letters of the document are formed 'directly' i.e. where the laser light strikes the photosensitive drum. Therefore, the background retains the positive charge (polarity) and the photosensitive discharged areas, correlating to the letters, become negatively charged. This is also known as 'Write-Black' or 'Blackwriting´
The letters of the document are formed 'indirectly' i.e. where the reflected light did not strike the photosensitive drum. Therefore, the letters retain the positive charge (polarity) and the photosensitive discharged 'background' becomes negatively charged. This is also known as 'Write-White' or 'Whitewriting´.