Valosähkökirjoitus

Valosähkökirjoitus, also known as electrophotography or xerography, is a dry copying process that uses static electricity and light to reproduce images. It is the fundamental technology behind most photocopiers and laser printers. The process typically involves a series of steps, beginning with a photoconductive drum that is initially given a uniform electrostatic charge.

When an image of the original document is projected onto the drum, the areas illuminated by light lose their charge, while the unlit areas retain their charge. This creates an electrostatic image on the drum's surface. Next, a charged toner powder, which is a dry ink, is applied to the drum. The toner particles adhere to the charged areas of the electrostatic image.

The toner image is then transferred from the drum to a sheet of paper, which is also given an electrostatic charge to attract the toner. Finally, the toner on the paper is fused into place, usually by heat and pressure, creating a permanent copy of the original document. Valosähkökirjoitus revolutionized document duplication by offering a fast, efficient, and chemical-free method for producing copies. Its development in the mid-20th century paved the way for modern office technology.