Use in Avionics
For other uses, however, the advantages of the penetron remained. Although it was not well suited to the dot-sequential method of color broadcast, that was only important if one was receiving over-the-air broadcasts. For uses where the details of the signal were not important, like in computer displays, the penetron remained a serious contender. When a full color gamut was not needed, the complexity of the penetron was further reduced and it became very attractive. This lent it to custom applications like military avionics, where the nature of the input signal was not important and the developer was free to use any signaling style they wished.
In the avionics role the penetron had other advantages as well. Its use of phosphors in layers instead of stripes meant that it had higher resolution, three times that of the RCA system. This was very useful for radar display and IFF systems, where the images were often overlaid with textual cues that required high resolution to be easily readable. Additionally, since all of the signal reached the screen in a penetron, as opposed to 15% of it in a shadow mask tube, for any given amount of power the penetron was much brighter. This was a major advantage in the avionics role where power budgets were often quite limited, yet the displays were often hit with direct sunlight and needed to be very bright. The lack of the shadow mask also meant the penetron was much more robust mechanically, and didn't suffer from color shifting under g-loads.
Penetrons were used from the late 1960s to the mid-1980s, mostly for radar or IFF systems where two-color displays (green/red/yellow) were commonly used. Improvements in conventional shadow masks removed most of its advantages during this period. Better focusing allowed the size of the holes in the shadow mask to increase in proportion to the opaque area, which improved display brightness. Brightness was further improved with the introduction of newer phosphors. Problems with doming were addressed through the use of invar shadow masks that were mechanically robust and attached to the tube using a strong metal frame.