Low power discharge lamp with high efficacy

Abstract

In order to achieve a discharge lamp suited to operate under reduced nominal power of e.g. 20-30 W, a lamp is proposed with two electrodes ( 24 ) arranged at a distance in a discharge vessel ( 20, 120 ) for generating an arc discharge. The discharge vessel ( 20,120 ) has a filling with a substantially free of mercury and comprises a metal halide and a rare gas. The lamp ( 10, 110 ) further comprises an outer bulb ( 18 ) arranged around the discharge vessel at a distance (d 2 ). The outer bulb ( 18 ) is sealed and has a gas filling of a thermal conductivity (λ). The inner diameter (d 1 ) of the discharge vessel is preferably in a range from 2-2.7 mm. The wall thickness (w 1 ) is in a range from 1.4-2 mm. A heat transition coefficient (λ/d 2 ) is calculated as thermal conductivity (λ) at 800° C. of the outer bulb filling divided by the distance (d 2 ). The so-defined heat 10 transition coefficient is below 150 W/(m 2 K).

The invention claimed is: 
     
       1. A high intensity discharge lamp, comprising:
 a discharge vessel defining a discharge space being essentially free of mercury and containing at least a metal halide and a rare gas; 
 two electrodes disposed within the discharge vessel for generating an arc discharge a wall forming the discharge space disposed between the electrodes, the wall having substantially circular cross-section with an inner diameter (d 1 ) and a wall thickness (w 1 ), and 
 an outer bulb surrounding the discharge vessel and disposed at a distance (d 2 ) from a central position of an outer surface of the discharge vessel between the electrodes, the outer bulb being sealed and containing a gas filling having a predetermined thermal conductivity (λ) at 800° C., wherein 
 the wall thickness (w 1 ) ranges from about 1.4 mm to about 2 mm, 
 the distance (d 2 ) ranges from about 0.3 mm to about 0.8 mm, and 
 a heat transition coefficient (λ/d 2 ) calculated as said thermal conductivity (λ) divided by said distance (d 2 ) ranges from about 10 W/(m 2 K) to about 100 W/(m 2 K). 
 
     
     
       2. Lamp according to  claim 1 , wherein said inner diameter (d 1 ) ranges from about 2 mm to about 2.7 mm. 
     
     
       3. Lamp according to  claim 1 , wherein the gas filing consists essentially of Xe, Ar, N 2 , or O 2 . 
     
     
       4. Lamp according to  claim 1 , wherein the gas filling has a pressure of 10 mbar to 1 bar. 
     
     
       5. Lamp according to  claim 1 , wherein the gas filling has a lower thermal conductivity at 800° C. than air. 
     
     
       6. Lamp according to  claim 1 , wherein the wall thickness (w 1 ) ranges from about 1.55 mm to about 1.85 mm. 
     
     
       7. Lamp according to claim 1, wherein said lamp has a nominal power 20-30 W. 
     
     
       8. Lamp according to claim 1, wherein said discharge vessel is made of quartz glass. 
     
     
       9. Lamp according to claim 1, wherein said outer bulb is made of quartz glass. 
     
     
       10. A high intensity discharge lamp, comprising:
 a discharge vessel defining a discharge space being essentially free of mercury and containing at least a metal halide and a rare gas;   two electrodes disposed within the discharge vessel for generating an arc discharge a wall forming the discharge space disposed between the electrodes, the wall having substantially circular cross-section with an inner diameter (d1) and a wall thickness (w1), and   an outer bulb surrounding the discharge vessel and disposed at a distance (d2) from a central position of an outer surface of the discharge vessel between the electrodes, the outer bulb being sealed and containing a gas filling having a predetermined thermal conductivity (λ) at 800° C., wherein   the wall thickness (w1) ranges from about 1.4 mm to about 2 mm,   the distance (d2) ranges from about 0.1 mm to about 1.4 mm, and   a heat transition coefficient (λ/d2) calculated as said thermal conductivity (λ) divided by said distance (d2) ranges from about 10 W/(m2K) to about 100 W/(m2K).   
     
     
       11. Lamp according to claim 10, wherein said inner diameter (d1) ranges from about 2 mm to about 2.7 mm. 
     
     
       12. Lamp according to claim 10, wherein the gas filing consists essentially of Xe, Ar, N2, or O2. 
     
     
       13. Lamp according to claim 10, wherein the gas filling has a pressure of 10 mbar to 1 bar. 
     
     
       14. Lamp according to claim 10, wherein the gas filling has a lower thermal conductivity at 800° C. than air. 
     
     
       15. Lamp according to claim 10, wherein the wall thickness (w1) ranges from about 1.55 mm to about 1.85 mm. 
     
     
       16. Lamp according to claim 10, wherein said lamp has a nominal power from about 20 W to about 30 W. 
     
     
       17. Lamp according to claim 10, wherein said discharge vessel is made of quartz glass. 
     
     
       18. Lamp according to claim 10, wherein said outer bulb is made of quartz glass. 
     
     
       19. A high intensity discharge lamp, comprising:
 a discharge vessel defining a discharge space being essentially free of mercury and containing at least a metal halide and a rare gas;   two electrodes disposed within the discharge vessel for generating an arc discharge a wall forming the discharge space disposed between the electrodes, the wall having substantially circular cross-section with an inner diameter (d1) and a wall thickness (w1), and   an outer bulb surrounding the discharge vessel and disposed at a distance (d2) from a central position of an outer surface of the discharge vessel between the electrodes, the outer bulb being sealed and containing a gas filling having a predetermined thermal conductivity (λ) at 800° C., wherein   the wall thickness (w1) ranges from about 1.4 mm to about 2 mm,   the distance (d2) is selected so that a heat transition coefficient (λ/d2) calculated as said thermal conductivity (λ) divided by said distance (d2) ranges from about 10 W/(m2K) to about 100 W/(m2K).   
     
     
       20. Lamp according to claim 19, wherein said inner diameter (d1) ranges from about 2 mm to about 2.7 mm. 
     
     
       21. Lamp according to claim 19, wherein the gas filing consists essentially of Xe, Ar, N2, or O2. 
     
     
       22. Lamp according to claim 19, wherein the gas filling has a pressure of 10 mbar to 1 bar. 
     
     
       23. Lamp according to claim 19, wherein the gas filling has a lower thermal conductivity at 800° C. than air. 
     
     
       24. Lamp according to claim 19, wherein the wall thickness (w1) ranges from about 1.55 mm to about 1.85 mm. 
     
     
       25. Lamp according to claim 19, wherein said lamp has a nominal power from about 20 W to about 30 W. 
     
     
       26. Lamp according to claim 19, wherein said discharge vessel is made of quartz glass. 
     
     
       27. Lamp according to claim 19, wherein said outer bulb is made of quartz glass. 
     
     
       28. A high intensity discharge lamp, comprising:
 a discharge vessel defining a discharge space being essentially free of mercury and containing at least a metal halide and a rare gas;   two electrodes disposed within the discharge vessel for generating an arc discharge a wall forming the discharge space disposed between the electrodes, the wall having substantially circular cross-section with an inner diameter (d1) and a wall thickness (w1), and   an outer bulb surrounding the discharge vessel and disposed at a distance (d2) from a central position of an outer surface of the discharge vessel between the electrodes, the outer bulb being sealed and containing a gas filling having a predetermined thermal conductivity (λ) at 800° C., wherein   the wall thickness (w1) and the distance (d2) are selected so that a heat transition coefficient (λ/d2) calculated as said thermal conductivity (λ) divided by said distance (d2) ranges from about 10 W/(m2K) to about 100 W/(m2K).   
     
     
       29. Lamp according to claim 28, wherein said inner diameter (d1) ranges from about 2 mm to about 2.7 mm. 
     
     
       30. Lamp according to claim 28, wherein the gas filing consists essentially of Xe, Ar, N2, or O2. 
     
     
       31. Lamp according to claim 28, wherein the gas filling has a pressure of 10 mbar to 1 bar. 
     
     
       32. Lamp according to claim 28, wherein the gas filling has a lower thermal conductivity at 800° C. than air. 
     
     
       33. Lamp according to claim 28, wherein the wall thickness (w1) ranges from about 1.55 mm to about 1.85 mm. 
     
     
       34. Lamp according to claim 28, wherein the distance (d2) ranges from about 0.1 mm to about 1.4 mm. 
     
     
       35. Lamp according to claim 28, wherein said lamp has a nominal power from about 20 W to about 30 W. 
     
     
       36. Lamp according to claim 28, wherein said discharge vessel is made of quartz glass. 
     
     
       37. Lamp according to claim 28, wherein said outer bulb is made of quartz glass.