Nipkow disk

If the sensor is made to control a light behind a second Nipkow disk rotating synchronously at the same speed and in the same direction, the image will be reproduced line-by-line.

One of the advantages of using a Nipkow disk is that the image sensor (that is, the device converting light to electric signals) can be as simple as a single photocell or photodiode, since at each instant only a very small area is visible through the disk (and viewport), and so decomposing an image into lines is done almost by itself with little need for scanline timing, and very high scanline resolution.

Some means of synchronizing the disks on the two devices must also be devised (several options are possible, ranging from manual to electronic control signals).

These facts helped immensely in building the first mechanical television accomplished by the Scottish inventor John Logie Baird, as well as the first "TV-Enthusiasts" communities and even experimental image radio broadcasts in the 1920s.

So the ideal Nipkow disk should have either a very large diameter, which means smaller curvature, or a very narrow angular opening of its viewport.

Another significant disadvantage lay with reproducing images at the receiving end of the transmission which was also accomplished with a Nipkow disk.

The actual amount of light gathered is instantaneous, occurring through a very small aperture, and the net yield is only a microscopic percentage of the incident energy.