Patent Publication Number: US-6906464-B2

Title: Red incandescent automotive lamp and method of making the same

Description:
TECHNICAL FIELD 
     This invention relates generally to incandescent lamps and, more particularly, to automotive exterior lamp assemblies used to provide turn signal, tail lamp, and braking signal lighting functions. 
     BACKGROUND OF THE INVENTION 
     Governmental regulations throughout most of the world require the use of certain colors of light for automotive signaling functions. In particular, red light having specific chromaticity boundaries is typically required for rear tail lamps and brake lamp signaling, and can be used as well for rear turn signals. To achieve this red light, clear incandescent lamps are typically used in a conjunction with a red filter lens. However, the use of a red exterior filter lens can limit the aesthetic styling of the vehicle. Also, in the event the lens is broken open, exposing the lamp, the non-red wavelengths of the emitted light may no longer be filtered out. 
     Accordingly, various approaches for producing red incandescent lamps have been investigated and proposed over the years. The most common approach is to apply a red pigment to the exterior surface of a standard clear glass lamp. However, while pigments that produce suitable filtering of the light have been known for years, they are not commonly used in automotive applications because the level of pigment concentration required to obtain the proper coloration of the light is so high that the resulting luminance level of the emitted light is too low. 
     It is therefore an object of this invention to provide an automotive incandescent lamp that provides a red colored light output which meets the applicable governmental requirements for both spectral content and intensity. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, there is provided a red incandescent lamp having a sealed lamp envelope formed from an amber glass, a filament located within the lamp envelope, and a coating applied to an external surface of the envelope, wherein the coating contains a red pigment. The amber glass provides initial filtering of the shorter wavelengths of visible light, so that the red pigment has to filter out less light and therefore can be applied in a manner that does not significantly impact the overall opaqueness of the lamp. As a result, the lamp produces the desired red colored light at a higher total light output than conventional red painted or coated bulbs. 
     In accordance with another aspect of the invention, there is provided an incandescent lamp that emits red light. The lamp includes a sealed vitreous envelope, a filament located within the envelope, and a pigmented coating over at least a portion of the envelope. The envelope is formed from a vitreous material that is at least partially opaque to visible light having a wavelength below 550 nm. The coating is applied to the external surface of the envelope and contains a pigment that is at least partially opaque to visible light having a wavelength below 600 nm. 
     In accordance with yet another aspect of the invention, a method of manufacturing an automotive lamp is provided using both the glass and pigmented coating compositions described above. The method uses a segment of glass tube having the above-noted composition; that is, an amber glass or other vitreous material that at least partially blocks visible light below 550 nm. First, one end of the glass tube is softened using heat and then blown into a globe using a mold. Then, a filament is inserted into the other end of the glass tube. Finally, a sealed envelope is formed containing the filament, and this is done by softening that other end of the glass tube using heat and sealing that other end by melting of the glass together with the light emitting element contained inside. Thereafter, the pigmented coating is applied. 
     The coating can include any suitable pigment for producing red light including inorganic pigments such as, for example, iron oxide. The coating can be applied in a thickness of between 0.5 and 1.5 thousandths of an inch, although a thinner or thicker coating can be used as appropriate for a particular application. Similarly, the concentration of the pigment in the coating can be varied up or down with the coating thickness depending upon the density of the pigmentation. 
     A lamp so constructed can provide a red color that meets both colorimetry and luminance requirements under the applicable SAE and ECE requirements for exterior vehicle lamps. The envelope can be formed into a wedge base lamp to produce GT-8 and other industry-standard lamps. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A preferred exemplary embodiment of the invention will hereinafter be discussed in conjunction with the appended drawings, wherein like designations denote like elements, and wherein: 
         FIG. 1  is a front view of an automotive lamp constructed in accordance with the invention; and 
         FIG. 2  is a side view of the automotive lamp of FIG.  1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to  FIGS. 1 and 2 , there is shown an automotive lamp  10  which in general comprises a sealed glass envelope  12  containing a filament assembly  14  and having an exterior coating  16  of red pigment. As used herein, an “automotive lamp” refers to a lamp that meets one or more automotive regulations or standards for the lamp. Such regulations and standards are well known to those skilled in the art. Envelope  12  is formed from an amber-colored glass and includes a sealed lower portion  18  and an upper portion  20  having a sealed interior region  22  in which there is provided an inert gas fill  24 . A sleeve  25  is attached over the press-sealed end  18 . 
     The filament assembly  14  includes a pair of filaments  26 ,  28 , a number of lead-in or support wires  30 - 32 , and a glass bridge  34  that maintains electrical isolation of the lead-in wires while providing additional structural support for the entire filament assembly  14 . The two filaments  26 ,  28  are spaced from each other within the interior region  22  and can be independently operated and used to provide two different levels of lamp illumination, as is known. The lower filament  26  is supported by lead-in wires  30  that extend downward from the filament  26 , through the bridge  34 , and into the sealed lower portion  18  which is in the form of a wedge base. These lead-in wires  30  extend through the wedge base  18  to an exposed location on the outside surface  36  of the glass envelope  12 . In particular, they exit the wedge base at its lowermost edge and run upward along the outer surface  36 , terminating at a protected location underneath the outer sleeve  25 . This construction provides an exposed portion of the wires for electrical connection of the lamp in circuit, and termination of the lead-in wires  30  underneath the outer sleeve helps prevent the exposed portions of the wires from being inadvertently bent outward away from the wedge base  18 . The outer sleeve  25  is a resilient plastic piece that allows the lamp  10  to be securely, but removably, connected to a conventional socket (not shown), with the plastic sleeve cooperating with a conventional socket clip to retain the lamp within the socket in a known manner. A suitable socket design for the lamp  10  is disclosed in U.S. Pat. No. 5,486,991, the entire contents of which are hereby incorporated by reference. 
     The upper filament  28  is supported by lead-in wires  31  that are curved laterally as shown in  FIG. 2  to maintain suitable spacing from filament  26 , but that otherwise extend downward through envelope  12  and to an exposed location on outer surface  36  in the same manner as wires  30 . Referring back to  FIG. 1 , the upper filament  28  is also supported by a third support wire  32  which provides mechanical support for the filament at its center. This wire  32  extends downwardly through the bridge  34  and into the wedge base  18 , but is terminated there and does not extend to the exterior of the envelope since it is not used to provide operating power to the filament. 
     The glass composition is selected in conjunction with the pigmented coating to obtain the desired red spectral content of the emitted light at the desired intensity level. This is accomplished by using an amber glass (that is, glass that emits primarily amber light) coated with a layer of red pigment. The amber glass provides initial filtering of the shorter wavelengths of visible light, so that the red pigment has to filter out less light and therefore can be made less opaque. As a result, the lamp produces the desired red colored light at a much higher total light output than can be obtained by simply painting or coating a clear bulb. 
     The glass envelope can be made from any suitable vitreous material that filters out a substantial amount of the light below about 550 nanometers in wavelength. Such materials include cadmium-impregnated glass as is well known to those skilled in the art. Cadmium-free glass can be used as well, such as a glass having the following composition in the following weight percentages: 
     
       
         
           
               
               
               
             
               
                   
                   
               
             
            
               
                   
                 SiO 2   
                 72%   
               
               
                   
                 K 2 O 
                 9.1% 
               
               
                   
                 SrO 
                 5.7% 
               
               
                   
                 Na 2 O 
                 5.5% 
               
               
                   
                 BaO 
                 2.2% 
               
               
                   
                 CaO 
                 2.1% 
               
               
                   
                 Al 2 O 3   
                 1.9% 
               
               
                   
                 MgO 
                 1.0% 
               
               
                   
                 SO 3   
                  0.37% 
               
               
                   
                 MoO 3   
                  0.07% 
               
               
                   
                 Fe 2 O 3   
                  0.03% 
               
               
                   
                 P 2 O 5   
                  0.02% 
               
               
                   
                 Cl 
                  0.01% 
               
               
                   
                 TiO 2   
                 trace. 
               
               
                   
                   
               
            
           
         
       
     
     Glass having this specific composition can be obtained from Maeda Glass Co., LTD, of Tokyo, Japan, and it will be appreciated that these weight percentages can be varied within two percent without significantly impacting the amber color filtering effect of the glass. 
     When used for automotive exterior signal lighting, it should be noted that, although amber colored glass meeting SAE and/or ECE color requirements can be used, other amber or yellow colored glasses not meeting those requirements can be used as well, as long as the combined color filtering of the colored glass and red pigment results in an overall light output that meets the applicable requirements for red color. 
     The coating  16  can be any suitable composition that includes a pigment capable of filtering out a substantial amount of light below 600 nanometers in wavelength. Inorganic pigments such as iron oxide can be used for this purpose, as is known in the art. The thickness of the pigment coating is selected in conjunction with the concentration (density) of the pigment to obtain the desired color shift and total light output. Preferably, the coating thickness is in the range of 0.5 to 1.5 mils. 
     For purposes of manufacturing the lamp, the amber glass is initially formed into an elongated tube, with the glass tube then being cut into segments of suitable length for manufacturing individual bulbs. One end of the segment of glass tube is softened using heat and then blown into a globe then cut to length to make an individual bulb. This can be done using a mold with the tube being expanded by air pressure while it is softened to form the enlarged upper portion  20  shown in  FIGS. 1 and 2 . Then, the filament assembly  14  is inserted into the other end of the glass tube. This filament assembly is pre-manufactured using the bridge  34  to hold the lead-in wires and filaments together as a single unit. Next, a sealed envelope is formed containing the light emitting element, and this is done by softening the then still open end of the glass tube using heat and sealing that open end by melting of the glass together with the light emitting element contained inside. This can be done using a press to seal the glass together and form the wedge-shaped lower portion  18 . For purposes of working the glass, it can be softened at about 690° C. with a working temperature of about 1150° C. To remove the air during this sealing operation, the envelope is flushed with krypton while being sealed. Also, a zirconium getter is placed into the interior region  22  before sealing to absorb any residual oxygen. 
     Using the manufacturing process, the envelope can be formed into a wedge base lamp to produce GT-8 and other industry-standard lamp configurations. Once the lamp has been sealed, the coating  16  is applied using any of a number of different techniques that will be well known to those skilled in the art. Such coating techniques include spraying and dipping. The coating  16  is applied to at least a portion of the exterior surface of the envelope  12 , as shown, and can be applied to the entire exterior, if desired. Thereafter, the lead-in wires are bent back over the outer surface of the press-sealed end  18  and the sleeve  25  is then fitted over the end  18 . 
     It will thus be apparent that there has been provided in accordance with the present invention an automotive lamp which achieves the aims and advantages specified herein. It will of course be understood that the foregoing description is of a preferred exemplary embodiment of the invention and that the invention is not limited to the specific embodiment shown. Various changes and modifications will become apparent to those skilled in the art. For example, the lamp can be manufactured using only a single filament. All such variations and modifications are intended to come within the scope of the appended claims.