||Increasing the viewing angle of LEDs and improving the ease with which they could be physically assembled into display panels were two of the key development activities of the early 1970s. Both of these problems were solved in the Hewlett-Packard 5082-44xx series, one of which is featured on this page. This product is representative of one of the earliest LEDs made in the ubiquitous T1¾ or 5mm package.
A new design which achieved a wide viewing angle without significant loss of intensity was invented by Roland Haitz at HP Labs, and consists of mixing powdered glass particles into the epoxy which forms the package encapsulation. This relatively simple innovation continues to be employed today in the majority of modern 5mm style LEDs. The glass particles act as diffusion centres which scatter light such that the upper surface of the device shows a substantially uniform intensity distribution which is viewable over a wide range of angles. By tinting the epoxy to the same hue as the wavelength of light emitted by the die, the on/off contrast was increased significantly.
A second improvement is the addition of a small metal flange around the base of the device. The increased diameter at its distal end serves as a stopper such that when LEDs are inserted through a hole into a control panel, they can all be inserted to the same depth. A small white dot is printed adjacent to the cathode lead wire to aid in its identification. Different colour dots were used for various LED types. The metal flange design existed in production only for a brief period. For obvious reasons it was relatively quickly superseded by a simplified design in which the flange was moulded directly into the epoxy encapsulation.