with competing systems by Philco and DuMont Laboratories. In 1939, RCA paid Farnsworth $1 million for his patents after ten years of litigation, and RCA began demonstrating all-electronic television at the 1939 World's Fair in New York City. The last mechanical television broadcasts ended in 1939 at stations run by a handful of public universities in the United States. Modern applications of mechanical scanning Since the 1970s, some amateur radio enthusiasts have experimented with mechanical systems. The early light source of a neon lamp has now been replaced with super-bright LEDs. There is some interest in creating these systems for narrow-bandwidth television, which would allow a small or large moving image to fit into a channel less than 40 kHz wide (modern TV systems usually have a channel about 6 MHz wide, 150 times larger). Also associated with this is slow-scan TV – although that typically used electronic systems utilising the P7 CRT until the 1980s and PCs thereafter. There are three known mechanical monitor forms: two fax printer-like monitors made in the 1970s, and in 2013 a small drum monitor with a coating of glow paint where the image is painted on the rotating drum with a UV laser. Digital Light Processing (DLP) projectors use an array of tiny (16 μm2) electrostatically-actuated mirrors selectively reflecting a light source to create an image. Many low-end DLP systems also use a color wheel to provide a sequential color image, a feature that was common on many early color television systems before the shadow mask CRT provided a practical method for producing a simultaneous color image. Another place where high-quality imagery is produced by opto-mechanics is the laser printer, where a small rotating mirror is used to deflect a modulated laser beam in one axis while the motion of the photoconductor provides the motion in the other axis. A modification of such a system using high power lasers is used in laser video projectors, with resolutions as high as 1024 lines and each line containing over 1,500 points. Such systems produce, arguably, the best quality video images. They are used, for instance, in planetariums. The long wave infrared cameras used in military applications such as giving fighter pilots night vision. These cameras use a high sensitivity infrared photo receptor (usually cooled to increase sensitivity), but instead of disks of lenses, these systems use rotating prisms to provide a 525 or 625 line