Abstract:
The invention provides a fluorescent lamp comprising a transparent lamp with a closed chamber filled with gas, a pair of electrodes disposed at opposite ends of the transparent lamp; a layer of dielectric omni-directional reflector disposed on the inner walls of the chambers for substantially fully reflecting ultraviolet light, and a fluorescent layer disposed on the layer of dielectric omni-directional reflector for reacting with the ultraviolet light to form visible light. The invention further discloses a flat lamp comprising the above-mentioned dielectric omni-directional reflector.

Description:
BACKGROUND  
       [0001]     The invention relates in general to a fluorescent lamp and a flat lamp. In particular, the invention relates to a fluorescent lamp and a flat lamp with a layer of dielectric omni-directional reflector.  
         [0002]     Cold cathode fluorescent lamps are a novel micro-illuminant usually applied in liquid crystal display, scanner, dashboard or picture frame because of high radiation intensity, uniform emission and formation in all kinds of shape.  
         [0003]      FIG. 1  is a cross-section of a conventional fluorescent lamp comprising a transparent lamp with a closed chamber filled with mercury vapor, Ar, Ne or Xe. A fluorescent layer  105  is formed on the inner wall of the transparent lamp, and a pair of electrodes  103   a ,  103   b  is disposed at opposite ends of the transparent lamp. When the opposite electrodes of the transparent lamp  103   a ,  103   b  are applied with a high voltage, the gas inside the transparent lamp  101  such as Ar is ionized. Excited electrons collide with the Hg atoms to radiate ultraviolet light and visible light, and the ultraviolet light  209  reacts with the fluorescent layer  105  to radiate visible light  211 . The ultraviolet light  209  cannot react with the fluorescent layer  105  completely, because part of the ultraviolet light  209  is absorbed by the inner wall of the chamber and converted into heat, or consumed when penetrating the chamber walls, thus reducing the conversion for visible light.  
       SUMMARY OF THE INVENTION  
       [0004]     The invention provides a fluorescent lamp and flat lamp, with a layer of dielectric omni-directional reflector. A dielectric omni-directional reflector is formed between a fluorescent layer and the inner wall of the lamp to reflect ultraviolet light penetrating the fluorescent layer, such that the ultraviolet light is confined within the fluorescent lamp and reflected repeatedly to fully react with the fluorescent layer and radiate visible light, thus improving conversion efficiency. In addition, the dielectric omni-directional reflector does not reflect visible light. The dielectric omni-directional reflector improves conversion and the emission efficiency, and reduces damage caused by ultraviolet light.  
         [0005]     Accordingly, the invention provides a fluorescent lamp comprising a transparent lamp with a closed chamber filled with gas, a pair of electrodes disposed at opposite ends of the transparent lamp, a layer of dielectric omni-directional reflector disposed on the inner wall of the chamber to fully reflect ultraviolet light, and a fluorescent layer disposed on the layer of dielectric omni-directional reflector to react with the ultraviolet light to form visible light.  
         [0006]     The invention further provides a flat lamp comprising a second substrate opposite to a first substrate, wherein at least one of substrates is a transparent substrate, at least one spacer disposed between the first and second substrates to provide a plurality of chambers filled with gas therebetween, a layer of dielectric omni-directional reflector is disposed on the inner wall of the chamber to fully reflect ultraviolet light, and a fluorescent layer disposed on the layer of dielectric omni-directional reflector to react with the ultraviolet light to form visible light. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]     The invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
         [0008]      FIG. 1  is a cross-section of a conventional fluorescent lamp;  
         [0009]      FIG. 2  is a cross-section of a fluorescent lamp with a layer of dielectric omni-directional reflector according to an embodiment of the invention; and  
         [0010]      FIG. 3  is a cross-section of a flat lamp with a layer of dielectric omni-directional reflector according to an embodiment of the invention.  
         [0011]      FIG. 4  is a cross-section of an omni-directional reflector according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0012]      FIG. 2  is a cross-section of a fluorescent lamp with a layer of dielectric omni-directional reflector according to an embodiment of the invention. The fluorescent lamp comprises a transparent lamp  201  such as glass lamp, and a pair of electrodes  203   a ,  203   b  disposed at opposite ends of the lamp  201 . The fluorescent lamp in  FIG. 1  is a cold cathode fluorescent lamp (CCFL), wherein the electrodes are located inside the lamp, and or alternatively located outside the lamp such as an external electrode fluorescent lamp (EEFL). A layer of dielectric omni-directional reflector  205  and a layer which can react with the ultraviolet light to radiate visible light, such as fluorescent layer  207 , are disposed on the inner wall of the fluorescent lamp  200 , wherein the dielectric omni-direction layer  205  is disposed between the fluorescent layer  207  and the inner wall of the fluorescent lamp  200 .  
         [0013]     The dielectric omni-directional reflector has a periodic stacked structure, transparent in the range of visible light wavelength. The energy gap in the periodic stacked structure may filter the incident light allowing light of predetermined wavelength to pass. The bandwidth of the energy gap and corresponding frequency thereof may be adjusted by different dielectric materials and stacking periods. It is noted that one-dimension periodic structures may be provided with omni-directional energy gap with appropriate dielectric materials and stacked periods thereof. In other words, the modes of electromagnetic wave toward the periodic stacked structure from all directions cannot extend in a predetermined range of frequencies. The approximate equation of the energy gap is as follows:  
         Δω     2   ⁢   c       =         α   ⁢           ⁢     cos   ⁡     (     -         A   -   2       A   +   2           )               d   1     ⁢     n   1       +       d   2     ⁢     n   2           -       α   ⁢           ⁢     cos   ⁡     (     -         B   -   2       B   +   2           )               d   1     ⁢         n   1   2     -   1         +       d   2     ⁢         n   2   2     -   1                   
 
 Wherein n1, n2 are reflective coefficients of dielectric material, 
 
 d1 and d2 are thicknesses of the dielectric material, 
 
 c is the velocity of light, 
 
 ω is angle frequency, and 
 
 α is period. 
 
 Constants A and B are defined by:  
         A   ≡         n   2       n   1       +       n   1       n   2           ,     B   ≡           n   2     ⁢         n   1   2     -   1             n   1     ⁢         n   2   2     -   1           +           n   1     ⁢         n   2   2     -   1             n   2     ⁢         n   1   2     -   1           .             
 
         [0014]     For a predetermined ratio d 1 /a, normalized energy gaps (ω 2 −ω 1 /0.5(ω 2 +ω 1 )) can be adjusted by reflective coefficient ratios of different materials. Normalized energy gaps increase with the difference between reflective coefficients increase in each layers.  
         [0015]     The dielectric omni-directional reflector, transparent in the range of visible light wavelength comprises, at least two of SiO 2 , AlN, ZnO, Al 2 O 3 , Ta 2 O 3  and TiO 2 , with SiO 2  and Al 2 O 3  are preferred. As shown in  FIG. 4 , The dielectric omni-directional reflector has a periodic stacked structure, including alternating layers  401  and  403  of two materials with large index contrast. The layer  401  and  403  may be SiO 2  and Al 2 O 3 , which display a large enough index of refraction contrast to ensure a strong reflection at a large incidence angle. The dielectric stacked structure acts as a perfect mirror due to high omni-directional reflection regardless of polarization and incident angles. The layer of dielectric omni-directional reflector may be produced by nanotechnology such as self assembly, sol-gel, or other conventional optical deposition methods such as sputtering, E-gun, or CVD (chemical vapor deposition). The dielectric omni-directional reflector exhibits high reflectivity for light in a predetermined range of wavelength regardless of incident angles and polarization thereof. Using the periodic stacked structure consisting of SiO 2  and Al 2 O 3  as an example, the dielectric omni-directional reflector exhibits a reflectivity exceeding 95% for light in a predetermined range of wavelength regardless of incident angles and polarization.  
         [0016]     The dielectric omni-directional reflector generally comprises a host compound and a dopant activator, the host compound comprising sulfate, halogen-containing phosphate, phosphate, tungstate, silicate or inorganic fluorescent material, and the inorganic fluorescent material comprising Y 2 O 3 , YVO 4 , SrB 4 O 7 F, MgGa 2 O 4 , or combinations thereof, and the dopant activator comprising Mn, Cu, Hg, rare earth elements or transition metals of lanthanides. The dopant activator is a substitutional or interstitial material to adjust the wavelength of light radiated from the host compound. The color of the light is determined by the dopant activator such as rare-earth elements.  
         [0017]     The chamber of the fluorescent lamp is filled with gas such as inert gas or a combination of mercury vapors and the inert gas. The fluorescent lamp uses electricity to excite inert gas or combination of inert gas and mercury vapor to produce visible light and ultraviolet light. The ultraviolet light reacts with the fluorescent layer  207  to radiate visible light, but a part of the ultraviolet light passes through the fluorescent layer  207  without reacting with the fluorescent layer  207 . The dielectric omni-directional reflector  205  of the invention disposed between the fluorescent layer  207  and the transparent lamp  201  reflects the ultraviolet light, thus improving radiation efficiency and reducing the damage from ultraviolet light.  
         [0018]      FIG. 3  is a cross-section of a flat lamp  300  according to the invention. The flat lamp  300  comprises a first substrate  301  and a second substrate  303  opposite thereto, wherein at least one of the substrates is a transparent substrate such as glass or transparent plastic. The first substrate  301  is made of glass or transparent plastic, and the second substrate  303  is made of glass or transparent plastic. The first and second substrates  301 ,  303  may be the same or different. A plurality of spacers  305  are disposed between the first substrate  301  and second substrates  303  to provide a plurality of chambers  311  therebetween. Although the chambers  311  illustrated in  FIG. 1  are isolated, the chambers may connect to each other, and the spacers  305  may be isolated between the first and second substrates  301 ,  303  or integral with the first or second substrates  301 ,  303 . The spacers  305  may be in the form of a stick, a plurality of columns or a crisscross.  
         [0019]     The chamber  311  is filled with gas such as inert gas or a combination of mercury vapor and an inert gas. A fluorescent layer  309  and a layer of dielectric omni-directional reflector  307  are disposed on the inner wall of the chamber  311 , wherein the layer of dielectric omni-directional reflector  307  is disposed between the fluorescent layer  309  and the inner wall of the chamber  311 . The dielectric omni-directional reflector is a periodic stacked reflector comprising at least two of SiO 2 , AlN, ZnO, Al 2 O 3 , Ta 2 O 3  and TiO 2 , with SiO 2  and Al 2 O 3  preferred. The layer of dielectric omni-directional reflector  307  may be formed by self-assembly, sol-gel or other optical deposition methods such as sputtering, E-gun or CVD (chemical vapor deposition). The dielectric omni-directional reflector may substantially fully reflect lights in a predetermined range of wavelength regardless of polarization. Using the periodic stacked structure consisting of SiO 2  and Al 2 O 3  as an example, the reflectivity exceeds 95% for lights in a predetermined range of wavelength.  
         [0020]     The flat lamp  300  uses electricity to excite inert gas or a combination of the inert gas and mercury vapors therein to produce visible light and ultraviolet light  209 . The ultraviolet light  209  then reacts with the fluorescent layer  309  to radiate visible light  211 , however, a part of the ultraviolet light  209  passes through the fluorescent layer  309  without reacting with the fluorescent layer  309 . The layer of dielectric omni-directional reflector  307  of the invention allows the visible light to pass, and reflects ultraviolet light which has passed the fluorescent layer  309 , improving radiation efficiency and reducing the damage from ultraviolet light.  
         [0021]     Finally, while the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. On the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.