The Penetron is a cathode ray tube with a voltage-sensitive screen that displays variable colors on layers of phosphors based on a beam penetration mechanism.

Penetron screens were commercially manufactured from late 1960s until mid- 1980s for avionics and radar application due to their higher resolution compared to conventional CRTs.^[1] Widely used CRT screens have two major features limiting the resolution: first, the spot size is limited by the shadow mask; second, each color pixel occupies the area three times larger than the area required for single color phosphor dot. In the penetron cathodoluminescent screen (CLS) different colors are displayed within the same area of the screen. Due to this fact, and also thanks to the absence of the shadow-mask the resolution of the Penetron screens inherently is limited only by the beam spot and, to a lesser degree, by phosphor grain size.

The conventional penetron screens consisted of two different layers made of transparent phosphors separated by a dielectric barrier layer. At low accelerating voltages, the electron beam is totally absorbed in a phosphor layer closest to the electron gun thus producing one output color, normally the red signal, while at higher voltages the beam penetrates through the first phosphor layer and excites the second (green) layer closest to the viewer. Intervening colors, (yellow or orange) are produced at intermediate acceleration voltages. Most penetron CRTs have layers of red and green phosphors on the interior of the faceplate providing simpler and higher resolution displays than color-mask tubes, but they cannot produce shades of blue.^[2]

Although there are technical difficulties extending the penetron approach to a display with a full color gamut, using multiple layers of color phosphors, the high resolution makes the penetron idea attractive for special applications requiring very high readability and color contrast. Therefore, penetron displays provide the benefit of smooth continuous lines without any color fringing, but also the drawback of increased electronic circuit complexity.^[3]

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