||Fairchild's FLV102 was one of the company's most popular early devices, and the technological step on which it was developed led the company into a position of dominance in the discrete LEDs market for much of the 1970s.
Earlier devices were packaged in small metal cans having a highly reflective inner surface - good for maximum light extraction. However the total quantity of light produced was tiny by today's standards, and visibility was often a problem in a normally lit room. Indeed the light level produced was so low that in applications where the LED was used as an indicator on a control panel, it was sometimes difficult to be sure whether or not it was actually illuminated! When viewing from certain angles, incident light from outside could be reflected within the metal package and give the incorrect impression that the device was energised.
These difficulties were partially solved by switching from the original water-clear lenses to tinted materials intended to absorb wavelengths other than those of the LED's own emission. Fairchild's innovation was to employ a black ceramic transistor header for the rear of the package and to mould the plastic lens over this. The resulting design is very successful at absorbing incident light from outside and greatly increases the on/off contrast. The original device to feature this design was the FLV100 which is similar but has a clear red hemispherical lens for fibre optic applications. The little-known FLV101 was a version of that having a frosted lens to widen its viewing angle, but the near 180° emission made it far too weak as an indicator. The FLV102 offers improved visibility thanks to a modified lens shape which narrows viewing angle to double the centre intensity.