Abstract:
There is herein described a lamp having a light-transmissive envelope, a tungsten-halogen capsule and a coating disposed on the surface of the light-transmissive envelope or doped in the light-transmissive material. The light-transmissive envelope may comprise a light-transmissive material. The tungsten-halogen capsule can be positioned inside the light-transmissive envelope.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of and claims the benefit of and priority to U.S. Utility application Ser. No. 13/476452, filed May 21, 2012, entitled “MODIFIED SPECTRUM INCANDESCENT LAMP” which claims the benefit of and priority to U.S. Provisional Application Ser. No. 61/534343, filed Sep. 13, 2011, entitled “MODIFIED SPECTRUM GENERAL SERVICE INCANDESCENT LAMP” both disclosures of which are hereby incorporated by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    This invention relates to incandescent lamps. In particular, this invention relates to incandescent lamps containing tungsten-halogen capsules. 
       BACKGROUND 
       [0003]    The Energy Independence &amp; Security Act of 2007 (EISA) set minimum efficiency standards for many of the common incandescent lamps, and these standards go into effect during subsequent years. Many incandescent lamps, including the A-line incandescent lamps with medium screw bases that have become commonplace in residential and amenity areas, do not have sufficiently high luminous efficacies, defined as lumens per watt (LPW), to meet these new efficiency standards. Compact fluorescent lamps are one technical solution for providing replacement lamps with sufficient luminous efficacies. However, consumers do not desire the color of the compact fluorescent lamps. As a result, the lamps have not been greeted with enthusiasm in the marketplace. 
         [0004]    Modified Spectrum General Service incandescent lamps, hereinafter referred to as “modified spectrum lamps,” are a category of lamps defined by EISA. According to the definition, such modified spectrum lamps have desirable color properties for general lighting purposes but they are not sufficiently saturated in color to be classified in the defined category of Colored Lamps. EISA requires that the modified spectrum lamps not be more than about 25% below the LPW requirements for the category of General Service Incandescent Lamps. 
         [0005]    EISA provides the lumen requirements for General Service Incandescent Lamps and Modified Spectrum Incandescent Lamps. For example, a 72 Watt General Service Incandescent Lamp needs to have 1490-2600 lumens. Accordingly, a 72 Watt Modified Spectrum Incandescent Lamp needs to have 1118-1950 lumens. 
         [0006]    There are several commercially available A-line incandescent lamps in the Modified Spectrum class at the present, for example GE Reveal®, Philips Natural Light™, and Osram Sylvania Living Spaces™. These are conventional gas-filled incandescent lamps with either a tinted bulb glass or a tinted internal powder coating to cause slight deviations in the spectra of the light after it has been emitted directly from the filament. Chromaticity ranges of these lamps are shown in  FIG. 1  on a 1931 CIE chromaticity diagram. 
         [0007]    The GE Reveal lamps are based on the absorption of neodymium. Introduction of neodymium causes the color temperature (CT) of the filament-emitted light to increase with small neodymium concentrations. At sufficiently large neodymium concentrations, the CT decreases but the efficacy losses become unreasonable. The chromaticity is well below the blackbody locus meaning that the lamps have magenta tints. 
         [0008]    Conversely, Osram Sylvania Living Spaces and Philips Natural Light lamps increase the CT of the filament-emitted light with reasonable increases of colorant concentration. The chromaticity remains closer to the blackbody locus meaning that the light does not take on the magenta tint associated with the neodymium lamps. A principle visual characteristic of the light from these lamps is that it tends to look somewhat less yellowish than the direct filament-emitted light. Such lamps tend to be more flattering to human complexion than compact fluorescent lamps. In addition, the lamps render a generally preferred appearance of objects with strong red reflective properties, i.e., where the spectral reflectance curve is high at wavelengths above about 620 nm. 
         [0009]    These lamps have an undesirable feature that the color temperature is above the color temperature of comparable wattage of standard incandescent lamps. The color temperature range of standard incandescent lamps is usually considered to be the desirable range for residential and amenity applications. Lower color temperature may often be preferred. Furthermore, for residential and amenity applications the appearance of warmth is usually desirable where the lower color temperatures tend to be more flattering to human appearance. Other psychological factors, such as those used to evaluate quantitatively color preference for light sources, also are involved in explaining such desires and preferences. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows the chromaticity ranges of prior art lamps on a 1931 CIE chromaticity diagram. 
           [0011]      FIG. 2  is a schematic illustration of a lamp according to an embodiment of the present invention. 
           [0012]      FIG. 3  shows the chromaticity range of a lamp according to an embodiment of the present invention on a 1931 CIE chromaticity diagram. 
           [0013]      FIG. 4  shows the effective spectral transmittances of a lamp having different coating concentrations. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims taken in conjunction with the above-described drawings. 
         [0015]    With reference to  FIG. 2 , a lamp  200 , in accordance with a first embodiment of the invention is illustrated. The lamp  200  contains an outer envelope  210  and a tungsten-halogen capsule  220  inside of the outer envelope  210 . The tungsten-halogen capsule  220  contains a tungsten filament within an inert gas and a small amount of a halogen gas such as iodine or bromine. The combination of the halogen gas and the tungsten filament produces a chemical reaction known as a halogen cycle that increases the lifetime of the filament and prevents darkening of the bulb by re-depositing tungsten. The tungsten-halogen capsule can operate at a higher filament temperature than a standard gas-filled lamp. The higher operating temperature results in a filament-emitted light of a higher color temperature and higher luminous efficacy. 
         [0016]    A coating  211  is applied to the outer envelope  210 . The coating  211  is a diluted powder coating. The chemical composition of the powder is a base of, for example, precipitated silica and a composition of colorants. The volume of colorants may be between 5% -25% of the coating composition. The coating  211  can be applied at a thickness/density similar or equal to that of the soft white finish on currently available Osram Sylvania® lamps. The coating  211  is spectrally selective and partially absorptive. The coating  211  can be chosen to reduce the color temperature without a large loss of lumens and to move the chromaticity of the light to a point below the blackbody locus and at least four MacAdam steps from that of the filament-emitted light. Thus, the lamp  200  may have a chromaticity that conforms to the definition of a modified spectrum lamp under EISA. Table 1 provides exemplary compositions of the coating for a range of colorant percentages. 
         [0000]    
       
         
               
               
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
             
             
               
                   
                 Hi-Sil T-700 
                 67.5 
                 66.75 
                 66 
                 64.2 
                 62.4 
               
               
                   
                 PRECIPITATED 
               
               
                   
                 SILICA 
               
               
                   
                 BURGESS 50 
                 30.5 
                 30 
                 29.5 
                 28.5 
                 27.5 
               
               
                   
                 ALUMINUM 
               
               
                   
                 SILICATE 
               
               
                   
                 PIGMENT 
               
               
                   
                 C-896-2 CrSn 
                 0.35 
                 1.4 
                 2.44 
                 4.7 
                 7.05 
               
               
                   
                 PINK 
               
               
                   
                 RED IRON 
                 0.05 
                 0.2 
                 0.36 
                 0.7 
                 1.05 
               
               
                   
                 OXIDE R-2199 
               
               
                   
                 COUPLING 
                 1.6 
                 1.68 
                 1.75 
                 1.9 
                 2 
               
               
                   
                 AGENT 
               
               
                   
                   
               
             
          
         
       
     
         [0017]    The lamp  200  can have a power rating of 72 watts. However, embodiments are not limited to this power rating and can constructed to provide a power rating in a range of about 28-72 watts. The resulting color temperature of the lamp  200  can be 2800K. The lamp  200  can produce 1360 lumens at an efficacy of about 19 LPW. The resulting color rendering index of the lamp can be about 99. Other embodiments can be provided with a lumen in range from about 232 to about 1950. Embodiments can also be designed to have a life of 1000-5000 hours. 
         [0018]    Increasing the concentration of colorant in the coating may allow for a reduction in the density and/or thickness of the coating. For example, a 10% colorant composition coating may have a thickness/density similar or equal to that of the current soft white finish. A 25% colorant composition may also be used with a thickness/density slightly less than that of the current soft white finish. 
         [0019]    The color temperatures, lumens, and CRIs of lamps according to embodiments with varied coating densities and/or concentrations are shown in Table 2. 
         [0000]    
       
         
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
               
                   
                   
               
               
                   
                 ~CT (K) 
                 ~lumens 
                 ~CRI (Ra) 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 1 
                 3010 
                 1490 
                 100 
               
               
                   
                 2 
                 2800 
                 1360 
                 99 
               
               
                   
                 3 
                 2700 
                 1290 
                 98 
               
               
                   
                 4 
                 2600 
                 1220 
                 98 
               
               
                   
                 5 
                 2500 
                 1140 
                 97 
               
               
                   
                   
               
             
          
         
       
     
         [0020]    Successively denser coatings produce lamps at 2800K, 2700K, 2600K, and 2500K. The range from 2500K to 2800K represents lamps that meet the efficacy requirements of a modified spectrum lamp. These lamps meet the need for lower color temperature appropriate for residential and amenity general lighting applications while satisfying the standards for modified spectrum lamps. 
         [0021]    In another embodiment, a thin, substantially non-absorbing, diffuse coating may be placed between a colorant layer and the bulb glass. The diffuse coating may eliminate the colored appearance caused by colorant, in case a white-appearing bulb is desired. 
         [0022]    Design of the lamp system can be done through the measurement of an effective spectral transmittance, τ(λ) eff , of the coating or bulb wall transmittance. This is a function of wavelength and is affected by the spectral power distribution of the filament-emitted light at each wavelength in the visible spectrum. An effective spectral transmittance is also affected by both the direct transmission through the coating and the multiple internal reflections of light from a spectrally selective surface. Quantities such as color temperature, chromaticity, and luminous flux of the light from the lamp can be calculated based on the effective spectral transmittance. 
         [0023]    For cases where attenuations are kept low to maintain high luminous efficacies, a semi-empirical equation based on classic radiative transfer technique for multiple reflections can be used: 
         [0000]      τ(λ) eff =1/[1+ g (λ) k]   (1);
 
         [0024]    where function g(λ) is a measure of the spectral effect, and k is a measure of colorant concentration or coating thickness. Function τ(λ) eff  is measured from the spectral emission of a lamp prepared with a coating material A having concentration of k. Function g(λ) can be calculated using the equation (1). Since function g(λ) is known for the lamp, effective spectral transmittance of the lamp with the coating material A having a lower concentration can be predicted.  FIG. 4  shows both the predicted and measured effective spectral transmittances of the same lamp with the coating material A having a lower concentration. The calculated result matches the experimental measurement. 
         [0025]    While the principles of the invention have been described herein, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation as to the scope of the invention. Reference numerals corresponding to the embodiments described herein may be provided in the following claims as a means of convenient reference to the examples of the claimed subject matter shown in the drawings. It is to be understood, however, that the reference numerals are not intended to limit the scope of the claims. Other embodiments are contemplated within the scope of the present invention in addition to the exemplary embodiments shown and described herein. Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention, which is not to be limited except by the recitations of the following claims.