power that travels through the red layer and into the green. Yellow can be produced by hitting the same location on both sweeps. In a display where the colors are either on or off and various brightness levels do not have to be created, the system can be further simplified by removing the color selection grid and modulating the voltage of the electron gun itself. However, this also causes problems because the electrons will reach the screen faster when accelerated with higher voltages, which means that the deflection system has to be increased in power as well to ensure the scanning creates the same screen size and line widths on both passes. Several alternative arrangements of the penetron were experimented on to address this problem. One common attempt used an electron multiplier at the tube face instead of the selection grid. In this system a low-energy scanning beam was used, and magnets were set to cause the electrons to strike the sides of the multipliers. A shower of higher-energy electrons would then be released and travel to the layered phosphors of a normal penetron arrangement. It was later noticed that the beams emanating from the multipliers landed in rings, which allowed a new arrangement of phosphors in concentric rings instead of layers. The main advantage to the penetron is that it lacks the mechanical focusing system of a shadow mask television, which means that all of the beam energy reaches the screen. For any given amount of power, the penetron will be much brighter, typically 85% brighter. This is a major advantage in an aircraft setting, where power supply is limited but the displays need to be bright enough to be easily read even when directly lit by sunlight. The system is guaranteed to produce the correct colors in spite of external interference or the g-forces of maneuvering – a very important quality in aviation settings. The penetron also offered higher resolutions because the phosphor was continuous, as opposed to the small spots in a shadow mask system. Additionally, the lack of the shadow mask makes the penetron much more robust mechanically. Sinclair experimented with a variant of this technology on his early pocket TV screens, but was unable to produce an RGB version. Examples of these tubes exist as prototypes. References Citations Bibliography D. N. Jarrett, "Cockpit Engineering", Ashgate Publishing, 2005 David Morton, , Johns Hopkins University Press, 2007,