Patent GB-861256-A (GB)
Title: Improvements in self luminous lamps
IPC: H05B31/18
Filed: 1958-01-21
Abstract: 861,256. Luminescent materials and uses thereof. UNITED STATES RADIUM CORPORATION. Jan. 21, 1958 [April 2, 1957], No. 2031/58. Class 39(1). A self-luminous element for a lamp structure comprises a gas-tight envelope of translucent or transparent non-darkening material, a phosphor coating on a surface inside the envelope, the coating having a thickness corresponding to approximately 50 to 150 mgrs. of phosphor per sq. cm., and radioactive gas comprising tritium or krypton 85 within the envelope to excite the phosphor to luminescence, the gas being at a pressure of approximately 50-760+ mms., preferably 50- 400 mms., in the case of tritium, or 150- 760+ mms., preferably 150-400 mms. in the case of krypton 85. In the construction shown in Fig. 1 the self-luminous element 5 is of cerium glass and comprises a bulb 16 and a stem 17, the inner surface of the bulb 16 being coated with a layer 20 of phosphor crystals such as copper activated zinc-cadmium sulphide, zinc sulphide, zinc silicate, cadmium tungstate or cadmium sulphide. The phosphor is bound to the surface of the bulb by organic, inorganic or semi-organic adhesives such as butyl methacrylate, colourless epoxy resins such as "Araldite" 502 (Registered Trade Mark), or sodium or potassium silicate. The shortest distance from the centre of the bulb 16 to the phosphor coating 20 should be no greater than the average trajectory range of the betaparticles emitted by the radio-active gas. A lead screen 21 can be fixed to the top of the bulb 16 and light-reflecting material can be interposed between the screen and the bulb. The lamp structure comprises a cylindrical brass casing 1 to which is attached an aluminium shell 2 and a brass saddle cup 3. A polished aluminium or chrome-plated brass parabolic reflector 6 is secured to a ring member 7 which rests in the cup 3 and is cemented to the luminous element 5 by epoxy resin. A shield 9 of radiation-absorbing material such as lead can be interposed between the reflector 6 and the shell 2. Across the top of the reflector 6 is a translucent or transparent flat or lens-shaped cover 12 of methyl methacrylate or lead glass or cerium glass of sufficient density and thickness to absorb radioactive emanations. The cover 12 is held in place by an aluminium ring 13 secured to the rim 11 by screws 14 with the interposition of gaskets 15 of cork-like material such as that known as Wiso d. The luminous element 5 passes through a hole 4 in the saddle cup 3 and is retained by a cement 18 such as an epoxy resin such as "Araldite" (Registered Trade Mark) or Epon. Beneath the cement 18 is a plug 19 of lead or methyl methacrylate with the optional interposition of a lead disc. In a modified construction the bulb of the luminous element and the reflector are spherical. A further modified luminous element is shown in Fig. 3 and comprises a glass bulb 28 surrounded by a glass envelope 27, the bulb 28 containing air or being evacuated. A phosphor coating 32 is applied to the exterior, surface of the bulb 28 and a phosphor coating 33 to the inner surface of the envelope 27. The spacing between the coatings should preferably not exceed the average trajectory range of the radioactive gas introduced into the envelope 27. A lead shielding cap 36 is provided. The thickness of the phosphor coating 32 corresponds to approximately 150 mgrs. of phosphor per sq. cm. and that of the coating 33 to approximately 50-150 mgrs. per sq. cm. The coating 33 can be one phosphor crystal thick and the phosphor crystals used can be of approximately 8 to 10 microns thick. A floodlight or sign panel is shown in Figs. 4, 5 and 6 and comprises a sheet metal box 54 which can include shielding means against radioactive emanations. Angles 37 support a sign panel 38 retained by a tab 51. The panel 38 is of translucent glass covered with opaque paint except for unpainted sign letters. A cover 39 of cerium glass or plastic material is placed in front of the panel 38 and is retained by a metal frame 40. A longitudinal parabolic reflector 44 is held in brackets 41a, 41b and 41c by claws 45. The structure can be attached to a wall or other support 47 by plates 46. The luminous element comprises a straight tube 48, of a glass as previously referred to, coated on the inside with a phosphor 49 and filled with radioactive gas as previously referred to. A lead shield 50 may be provided. The tube 48 is retained by adjustable clamps 52 and 53 to produce uniformly or non-uniformly distributed light. To produce uniform distribution the focal axis of the reflector 44 runs along the front portion of the phosphor coating 49. The luminous element can be modified to comprise a double-walled structure formed by inserting a glass rod or closed glass tube centrally in tube 48 leaving a cylindrical space to form the gas chamber which is filled with krypton 85 or tritium and the two opposing walls of which are coated with phosphor. For use as a floodlight the sign panel 38 is omitted. Reference has been directed by the Comptroller to Specification 646,414