Patent Application
20080036384
Aspects of the exemplary embodiments disclosed herein relate to an electric lamp having a reflective end coat and a lamp assembly which includes the lamp as well as to a method of forming the exemplary lamp.
With reference to
As shown in
The reflector housing 14 may be formed, for example, from plastic, glass, or aluminum. The housing may be itself reflective or may have a reflective coating formed thereon which defines the reflective surface. In the case of a plastic housing, the coating may be provided on an interior surface of the housing. In the case of glass, the coating may be provided on an interior or exterior surface. The reflective surface may be a metal, such as silver or aluminum, or may be defined by a dichroic coating comprising multiple layers of alternating higher and lower refractive index materials. The reflective surface may be parabolic, elliptical, or other suitable shape.
The illustrated filament 20 comprises a helical coil, generally aligned with the axis X of the reflector housing. The filament is supplied with electric current by leads 36, 38, which extend into the interior 18 from a second end 40 of the vessel 16, adjacent the reflector. The leads may be connected with outer connectors by molybdenum foils in a pinch area 42 of the vessel.
In another embodiment, the lamp 12 includes two filaments which are aligned generally parallel to each other, one for low beam and one for high beam. One or both of the filaments may be somewhat offset from the central axis X. Such a lamp configuration may include three leads (the forward ends of the filaments being connected to the same lead) whereby different voltages are applied to the two filaments.
As show in
With continued reference to
The reflective layer 28 is formed from a reflective material which reflects more light than it absorbs and transmits. For example, at least about 70% of all incident visible light (typically in the range of about 400-700 nm) is reflected and less than about 30% is absorbed or transmitted, and in one embodiment, at least 80% or at least 85% of the visible light incident at the reflective layer/glass interface is reflected, and the percentage may be up to about 95%, or higher. Exemplary materials which may be used for the reflective layer 28 include Ag, Al, Au, Cr, Cu, Ni, Pd, Pt, Rh and combinations thereof, such as nickel chrome, stainless steel, and the like. In one embodiment, the reflective layer is formed from silver (Ag) or an alloy thereof. In one embodiment, the reflective layer is formed primarily from silver (e.g., at least 80% silver, or at least 95% silver). The silver layer 28 has a reflectance generally of about 85-97%. The remaining light (e.g., about 3-5%), is absorbed by the silver layer 28, rather than being transmitted.
The reflective layer 28 has a sufficient thickness t that it is substantially non transmissive to light in the visible range of the spectrum. For example, less than about 1% of incident light is transmitted through the layer 28, and in one embodiment, less than about 0.1% is transmitted. In the case of silver, for example, the layer 28 may be at least about 0.05 micrometers (μm) in thickness and can be up to about 10 μm or higher. In general, a thickness of at least 0.2 μm, and up to about 2 μm, e.g., less than about 0.4 μm, is suitable to ensure that pinpricks of light do not escape through discontinuities in the coating 28. For example, the layer 28 may have an average thickness of about 0.3 μm.
Where the reflector housing 14 is not hermetically sealed, oxygen inside the reflector housing may contribute to oxidation of the reflective coating 28, particularly when formed of silver. In one embodiment, a protective layer 52 covers the reflective layer 28 and substantially seals it against oxidation. The protective layer 52 is spaced from the vessel 16 by the reflective coating 28 and, in general, does not extend substantially beyond the reflective layer 28 along the sidewall 48. The protective layer 52 may be formed from a stable dielectric film, such as oxides and nitrides that are substantially light transmissive such that the reflective silver layer 28 is visible therethrough when viewed from an exterior of the lamp assembly. This enables a user to identify the lamp 12 as having the reflective coating and also provides a pleasing visual appearance to the lamp. Suitable dielectric films for forming the protective layer 52 include oxides and/or nitrides of silicon and/or tantalum, e.g., silicon dioxide, silicon nitride, or hydrogenated silicon oxycarbon (H:SiOC) complexes. In one embodiment, the protective layer 52 may be at least about 0.05 μm in thickness and in one embodiment, at least about 0.1 μm and can be up to about 10 μm, or more, e.g. less than about 0.2 μm.
In another embodiment, the protective layer 52 comprises a substantially non-transmissive (e.g., light absorbing) material. For example, a black light-absorbing layer may be a paint comprising a pigment, for example ethyl-silicate paint, with silicon or a mixture of transition metal oxides therein, for example of Fe, Mn, or Ti, as the black pigment.
In operation, the lamp vessel 16 is fitted to a lamp cap 54 and seated in an opening 56 in the reflector housing and connected to a source of power (not shown). An electric current is applied across the filament 20 to generate light in the visible region of the spectrum. The visible light is transmitted by the light transmissive portion of the vessel, including light which is first reflected by the reflective layer 28. In other embodiments, the light source 20 may be provided by a gas discharge generated in an arc gap between spaced electrodes.
The illustrated lamp 12 can meet standards for automotive lamps which set limits on the amount of light which is emitted in a forward direction (i.e., towards the window 32). Currently, the standard in the U.S. is provided by 49 C.F.R. 564-Replacement Light Source Information (Part 564) and in Europe by ECE Regulation R37. The lamp 12 may be of the H7 type (nominally 53.5 W, 1350 lumens).
The exemplary lamp 12 may have a light output in lumens which is at least about 10% higher than an equivalent lamp formed with a light-absorbing (black) end coat, and may be up to about 20%. In practice, because of the higher efficiency (lumens/watt), the lamp may be run at lower power than a conventional black end-coated lamp.
Suitable techniques for forming one or both of the layers 28, 52 include vacuum deposition, dip coating, spraying, and the like. The reflective layer 28, for example, is deposited by vacuum deposition methods, such as sputtering, Ion-Assisted-Deposition (IAD), physical vapor deposition (PVD) or chemical vapor deposition (CVD), or by other known processes, such as thermal evaporation or dip coating. For example, in magnetron sputtering, high energy inert gas plasma is used to bombard a target, such as silver. The sputtered atoms condense on the cold glass or quartz vessel 16. DC (direct current), pulsed DC (40-400 KHz), or RF (radio frequency, 13.65 MHz) processes may be used. The protective layer may be formed, for example, by magnetron sputtering a silicon-containing target in an oxygen atmosphere or by plasma enhanced chemical vapor deposition (PECVD) of a hydrogenated silicon oxycarbide polymer from a hexamethyldisiloxane (HMDSO) fluid, such as Wacker Silicone Fluid AK 0.65 (99%+HMDSO, <0.5 ppm CI) supplied by Wacker Chemical Corporation, Adrian, Mich., or alternatively hexamethyldisiloxane 99%+(<0.5 ppm CI) supplied by Alfa Aesar, Ward Hill, Mass.
An exemplary method of preparing the coated lamps is illustrated in
The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations.
