US 3875456

Patent Overview — US 3,875,456

Title: Multi-color semiconductor lamp

Patent number: US 3,875,456 A (US3875456A)

Assignee: Hitachi Ltd (listed as current and original assignee)

Inventor(s): Tsuyoshi Kano, Tadashi Saitoh, Atsushi Suzuki, Teruki Suzuki, Shigekazu Minagawa, Yoshiro Otomo

Dates: Priority date 1972-04-04; filing date 1973-04-04; granted/publication date 1975-04-01; anticipated expiration 1992-04-01. Legal status listed as "Expired - Lifetime."

Purpose (plain language): The patent addresses multi-color indicating devices, using a traffic signal lamp as a typical example. Prior devices used separate light sources at different positions for each color, requiring large space; moreover, non-emitting sources could reflect ambient light and be mistaken for lit ones. The stated objects are to provide a multi-color semiconductor lamp that emits different colors from what appears to be a single light source, occupies less space, and yields clear, distinct colors.

Scope (plain language): Multiple light-emitting diodes, each emitting a different color, are placed close together and covered by a common light-scattering layer, so light from any diode appears to originate from one and the same source. Different colors, or blends from simultaneous emission, can be selected by electrical control. Embodiments include: two diodes in a metal casing with a scattering layer and lens (FIG. 1); an inner reflecting surface with a transparent resin layer having a lens-shaped outer surface (FIG. 2); infrared luminescent diodes covered with resin layers containing different phosphorescent powders (FIG. 3); and further modifications (FIGS. 4–5), including fluorescent materials in the scattering layer. The scattering layer may comprise ground glass, fine alumina powder bonded with resin, or powdered phosphors bonded with resin. Three or more diodes are contemplated. Terminal leads and a common lead are described for energizing the diodes.

Source: https://patents.google.com/patent/US3875456/en

What the excerpt does not establish: Because the text is excerpted, it does not establish the full claims, the complete specification, the exact chemical compositions or proportions of materials, all drawing details, or the full text of the omitted portion of the description. It also does not establish any legal conclusions about validity or claim scope.