Abstract:
The present disclosure provides a device and method for exposing a person to ultraviolet radiation in tanning wavelengths which is emitted from a discharge lamp having a plurality of grooves formed in its outer periphery along a helical path. The discharge lamp includes, inter alia, an elongated vitreous tube, first and second electrode assemblies and a coating on the interior the interior of the tube. The coating is applied on an interior of the tube along the entire length for emitting ultraviolet radiation in tanning wavelengths when a voltage is applied across the first and second electrodes. In a first representative embodiment, the plurality of grooves are interconnected and the helical path is continuous. Alternatively, the plurality of grooves can be axially offset and the helical path can be discontinuous.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The subject application is a continuation-in-part of commonly owned U.S. patent application Ser. No. 10/077,279, filed Feb. 15, 2002, which is herein incorporated by reference in its entirety. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to discharge lamps, and more particularly, to a discharge lamp for use in tanning applications, wherein the lamp includes a vitreous tube having a series of grooves formed in its periphery.  
           [0004]    2. Background of the Related Art  
           [0005]    Discharge lamps have been in existence for many decades. Discharge lamps consist primarily of an elongated vitreous tube having axially opposed end seals and coated on the inside with phosphor powders which fluoresce when excited by ultraviolet light. Filament electrodes are mounted on the end seals of the tube and are connected to base pins which engage with the lamp housing. The elongated tube is filled with a rare gas, such as argon, and a drop of mercury.  
           [0006]    Discharge lamps typically operate at a relatively low pressure. In operation, an alternating current is applied to the electrodes which increases the electrode temperature and causes the emission of electrons therefrom. These electrons are accelerated by the voltage across the tube until they collide with the mercury atoms, causing them to be ionized and excited. When the mercury atoms return to their normal state, mercury spectral lines in both the visible and ultraviolet region arc generated. The ultraviolet radiation excites the phosphor coating to luminance. The resulting output is not only much higher than that obtained from the mercury lines alone, but also results in a continuous spectrum with colors dependent upon the phosphors used.  
           [0007]    Typically, the intensity of the ultraviolet radiation emitted from the discharge lamp differs along the length of the lamp, but does not vary dramatically nor are distinct regions of varying intensity created. In applications such as tanning, which will be discussed in more detail supra, it would be advantageous to have distinct regions of ultraviolet radiation intensity.  
           [0008]    Since the late 1970s, the practice of tanning, defined as the darkening of one&#39;s skin through exposure to ultraviolet (UV) radiation, has increased in popularity in the United States. Each person&#39;s skin reacts differently to UV radiation exposure, with the reaction being dependent upon genetically determined factors, such as the amount of melanin pigment already in the skin naturally and the capability of the person&#39;s skin to produce additional melanin (facultative pigmentation).  
           [0009]    Melanin is the dark pigment found in the retina, hair and skin, except for the palms of the hands, soles of the feet and lips. Without the protection afforded by the melanin pigment, a person&#39;s skin would burn when exposed to UV radiation. As stated above, the skin includes naturally occurring melanin pigment and produces additional melanin. Melanin is produced by special cells called melanocytes, which are located deep within the outer layer of the skin. When the melanocytes are stimulated by ultraviolet light, they utilize an amino acid called tyrosine to produce the pigment melanin. Since the melanin pigment is only able to absorb ultraviolet light of approximately 260-320 nanometers, UVB radiation is needed to achieve melanin production. UVA radiation which has a wavelength of approximately 320-400 nanometers can formulate melanin, but only when there is enough photosensitizing material already in the skin to trigger a UVB reaction. With the presence of UVB, melanocytes are stimulated to divide, creating more pigment cells. During this time, the epidermis thickens to form additional protection, a condition referred to as acanthosis.  
           [0010]    In the beginning stages of melanin production, the skin has very little melanin or radiation protection capabilities. As a result, UVA radiation is not blocked by melanin pigments and, due to its longer wavelength, penetrates the skin deeper than UVB, causing damage to the corium. Damage to this layer of the epidermis hastens aging and destruction of collagen and connective tissue. A UVA burn can be much more damaging because it is not felt due to its deep penetration.  
           [0011]    In order for the pigmentation process to be effective, melanin granules must be oxidized or darkened, which requires a high dose of long-wave UVA. Consequently, exposure to UVB radiation functions to create melanin pigment, while UVA exposure ensures the oxidation of the pigment. Together, a the proper combination of UV exposure operates to create a light-protection mechanism.  
           [0012]    It is well recognized that to obtain the desired uniform tan, a person&#39;s facial region often requires the application of more intense radiation than the body region. This is due to the higher levels of melanin pigment present in the face, resulting from a more frequent exposure to the sun than the body. Prior attempts at designing a tanning chamber which provides a more uniform tan have included a lamp assembly which utilizes separate and distinct bulbs in the facial region. More specifically, higher intensity metal halide bulbs are positioned in the facial region and lower intensity bulbs extend over the body.  
           [0013]    U.S. Pat. No 5,557,112 to Csoknyai et al. discloses a fluorescent lamp having distinct and adjacent first and second zones along its length with different ultraviolet radiation characteristics. The first zone of the lamp has a first fluorescent coating applied to the inner surface of the tube for producing ultraviolet radiation having desired radiation characteristics. The second zone of the lamp has a second fluorescent coating applied to the tube for producing ultraviolet radiation having radiation characteristics which are different from those produced in the first zone.  
           [0014]    Although these prior attempts may contribute to a more uniform tanning effect, they are more complicated to fabricate and maintain and are relatively expensive. This is especially true when the lamp is used in an application that requires more than two regions of varying intensity.  
           [0015]    The patent literature also includes disclosures concerning tubular lamp assemblies that include constricted portions or grooves. See e.g., U.S. Pat. Nos. 2,916,645 to Lemmers et al.; 3,129,085 to Olsen et al.; 4,825,125 to Lagushenko et al; 3,988,633 to Shugan et al.; and Des. 198,268. The prior art patent disclosures also teach conventional systems and processes for forming such constricted portions and/or grooves in tubular lamps.  
           [0016]    There is a continuing need for discharge lamps for use in applications such as tanning that provide enhanced lamp performance and/or energy delivery.  
         SUMMARY OF THE INVENTION  
         [0017]    The present invention is directed to and provides a discharge lamp which includes, inter alia, an elongated vitreous tube, first and second electrode assemblies and a coating on the interior the interior of the tube. The elongated vitreous tube has an outer periphery and axially opposed first and second ends which define an axial length for the tube therebetween. Preferably, the length of the vitreous tube is approximately 72 inches.  
           [0018]    The outer periphery has a plurality of grooves defined therein and positioned along an axially extending helical path. Additionally, the first electrode assembly is associated with the first end of the tube and the second electrode assembly is associated with the second end of the tube. A coating is applied on an interior of the tube along the entire length for emitting ultraviolet radiation in tanning wavelengths when a voltage is applied across the first and second electrodes.  
           [0019]    In a first representative embodiment, the plurality of grooves are interconnected and the helical path is continuous. Alternatively, the plurality of grooves can be axially offset and the helical path can be discontinuous.  
           [0020]    Preferably, the grooves are formed in the outer periphery of the tube so as to have a pitch of between about 2 inch and about 12 inch and a depth of between about 0.100 inch to about 0.250 inch. As used herein, groove pitch is defined as the distance from a point on a groove to a corresponding point on the next or adjacent groove measure parallel to the axis and is synonymous with the axial spacing. Additionally, it is envisioned that the grooves are formed in the outer periphery so as to have a ratio of the groove pitch to the groove depth of about between 8 (in/in) to about 120 (in/in).  
           [0021]    It is envisioned that the grooves are formed in the outer periphery so as to have a width of about 0.250 inch to 1.0 inch and a ratio of the groove pitch to the groove width of about between 2 (in/in) to about 48 (in/in). Additionally, it is presently envisioned, but not required, that the depth of each groove does not exceed 10 percent of the outside diameter of the tube.  
           [0022]    It is also envisioned that the discharge lamp of the present disclosure further includes a reflective coating on the interior of the vitreous tube and which is positioned radially inward of the coating. The reflective coating extends about a portion of the vitreous tube circumference.  
           [0023]    The present disclosure is also directed to a device for effectuating tanning of a person&#39;s skin. The tanning device includes, inter alia, a housing structure and a discharge lamp assembly. The housing structure has a body portion and a base portion. The body portion defines an internal tanning chamber which is adapted and configured for receiving the person.  
           [0024]    The discharge lamp assembly is disposed within the internal tanning chamber and includes an elongated vitreous tube, first and second electrode assemblies and a coating on the interior the interior of the tube. The elongated vitreous tube has an outer periphery and axially opposed first and second ends which define an axial length for the tube therebetween. Preferably, the length of the vitreous tube is approximately 72 inches. The outer periphery has a plurality of grooves defined therein and positioned along an axially extending helical path.  
           [0025]    The first electrode assembly is associated with the first end of the tube and the second electrode assembly is associated with the second end of the tube. A coating is applied on an interior of the tube along the entire length for emitting ultraviolet radiation in tanning wavelengths when a voltage is applied across the first and second electrodes.  
           [0026]    The present disclosure is also directed to a method of exposing a person to ultraviolet radiation. The method includes the steps of positioning a discharge lamp assembly in proximity to a person and energizing said discharge lamp for a period of time to effect skin tanning of said person.  
           [0027]    The discharge lamp includes an elongated vitreous tube having an outer periphery and axially opposed first and second ends which define an axial length for the tube therebetween. The outer periphery has a plurality of grooves defined therein and formed along a helical path. The lamp further includes a first electrode assembly which is associated with the first end of the tube and a second electrode assembly which is associated with the second end of the tube. A coating is applied to the interior of the vitreous tube along the entire length for emitting ultraviolet radiation in tanning wavelengths when a voltage is applied across the first and second electrodes. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]    So that those of ordinary skill in the art to which the subject invention pertains will more readily understand how to make and use the system and method described herein, preferred embodiments will be described in with reference to the drawings, wherein:  
         [0029]    [0029]FIG. 1 is an elevational view of a tanning chamber which includes a plurality of discharge lamps that are constructed in accordance with an embodiment of the present disclosure;  
         [0030]    [0030]FIG. 2 illustrates a sectional view of the tanning chamber of FIG. 1 taken along line  2 - 2 ;  
         [0031]    [0031]FIG. 3 a  illustrates a discharge lamp constructed in accordance with an embodiment of the present disclosure having a series of axially spaced grooves formed in a portion of the periphery of the tube;  
         [0032]    [0032]FIG. 3 b  is a cross-sectional view of the discharge lamp of FIG. 3 a  taken along line  3   b - 3   b  and illustrating an internal reflector coating disposed within the lamp core which defines an aperture window;  
         [0033]    [0033]FIG. 3 c  illustrates an exploded cross-sectional view of the area identified as  3   c  in FIG. 3 a;    
         [0034]    [0034]FIG. 4 a  is an elevational view of a discharge lamp constructed in accordance with an embodiment of the present disclosure having two regions of axially spaced apart grooves formed in the periphery of the vitreous tube;  
         [0035]    [0035]FIG. 4 b  is a cross-sectional view of the discharge lamp of FIG. 4 a  taken along line  4   b - 4   b  and illustrating the internal fluorescent coating;  
         [0036]    [0036]FIG. 5 a  is an elevational view of a discharge lamp constructed in accordance with an embodiment of the present disclosure having three distinct regions of axially spaced apart grooves formed in the periphery of the vitreous tube;  
         [0037]    [0037]FIG. 5 b  is a cross-sectional view of the discharge lamp of FIG. 5 a  taken along line  5   b - 5   b;    
         [0038]    [0038]FIG. 6 a  illustrates a discharge lamp constructed in accordance with an embodiment of the present disclosure having a helical groove path formed in the periphery of the tube;  
         [0039]    [0039]FIG. 6 b  is a cross-sectional view of the discharge lamp of FIG. 6 a  taken along line  6   b - 6   b  and illustrating an internal reflector coating disposed within the lamp core;  
         [0040]    [0040]FIG. 6 c  is an exploded cross-sectional view of the area identified as  6   c  in FIG. 6 a  which illustrates an exemplary groove depth according to the present disclosure;  
         [0041]    [0041]FIG. 7 illustrates a discharge lamp constructed in accordance with an embodiment of the present disclosure wherein axially spaced grooves are formed in the periphery of the tube in a helical pattern; and  
         [0042]    [0042]FIG. 8 illustrates a discharge lamp constructed in accordance with an embodiment of the present disclosure wherein the axially spaced grooves formed in the periphery of the tube are relatively tightly spaced. 
     
    
     DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0043]    Reference is now made to the accompanying figures for the purpose of describing, in detail, preferred embodiments of the present disclosure. The figures and accompanying detailed description are provided as examples of the disclosed subject matter and are not intended to limit the scope thereof.  
         [0044]    Referring now to FIGS. 1 and 2, there is illustrated a tanning chamber constructed in accordance with a preferred embodiment of the present disclosure and designated generally as reference numeral  100 . Tanning chamber  100  primarily includes tanning bed  10  and lamp assembly  20 . Tanning bed  10  is supported by leg members  12   a  and  12   b  and is generally configured so that surface  14  is parallel with the floor (not shown) and lamp assembly  20 . However, those skilled in the art would readily appreciate that tanning chamber  100  can be configured as a vertically oriented tanning booth without departing from the inventive aspects disclosed herein.  
         [0045]    Lamp assembly  20  includes housing  22 , electric contacts  24   a  and  24   b,  and fifteen (15) discharge lamps  50 . Discharge lamps  50  are electrically engaged with contacts  24   a  and  24   b  and are adapted and configured so as to emit ultraviolet light in the substantially downward direction when an alternating current is applied thereto. Lamps  50  will be discussed in greater detail supra. Those skilled in the art would readily appreciate that the quantity and spacing “s” of discharge lamps  50  can be selectively adjusted based on factors such as, but not limited to, the width of tanning chamber  100 , the distance between lamp assembly  20  and surface  14 , the outside diameter of lamps  50 , and the desired radiation intensity.  
         [0046]    A person “P” is positioned on surface  14  of tanning bed  10  such that the frontal region of person P faces lamp assembly  20 . As a result, the frontal region of person P is exposed to the ultraviolet light emitted from lamp assembly  20  and is tanned thereby. As shown in FIG. 1, discharge lamp  50  includes a first region  60  and second region  70  axially deployed or arranged along length L 1  (see FIG. 3 a ) of lamp  50 . The lengths of the first and second regions  60  and  70 , are identified as L 2  and L 3  respectively. The first region  60  is advantageously configured and dimensioned to be positioned over the facial portion of person P and the second region  70  is generally configured and dimensioned to extend over the body portion. In an exemplary embodiment of lamp assembly  20 , the length of the facial region, and thus L 2 , is approximately 18 inches.  
         [0047]    Referring now to FIGS. 3 a - 3   c,  there is illustrated lamp  50  which includes an elongated vitreous tube  52 , first and second end seals  54   a  and  54   b,  and first and second electrodes (not shown). Tube  52  has a phosphor coating  56  applied to interior surface  57  and has a drop of mercury disposed within central core  53 . Tube  52  has an outer periphery  58  which extends axially between the first and second end seals  54   a  and  54   b.  The overall length of tube  52  is identified as L 1 . Typically in a tanning application, such as illustrated herein, the overall length of tube  52  is approximately 72 inches or 6 feet. As would be readily appreciated by those skilled in the art to which the present disclosure appertains, the length of each region and the overall length of the tube can be selectively adjusted based on the intended application.  
         [0048]    The first electrode assembly is associated with the first end seal  54   a  and the second electrode assembly is associated with the second end seal  54   b.  Each electrode assembly includes pins  64   a  and  64   b  which electrically communicate with corresponding electrical contacts  24   a  and  24   b  associated with lamp assembly  20 . In an alternate embodiment, pins  64   a  and  64   b  can be replaced with a recessed double contact base or any other suitable electrical communication means, as would be readily appreciated by those skilled in the art.  
         [0049]    In operation, an alternating current is applied to the pins  64   a  and  64   b  which increases the temperature of the electrodes and causes the emission of electrons therefrom. These electrons are accelerated by the voltage across the tube  52  until they collide with the mercury atoms, causing them to be ionized and excited. When the mercury atoms return to their normal state, mercury spectral lines in both the visible and ultraviolet region are generated. The ultraviolet radiation excites the phosphor coating  56  to luminance and generates a higher intensity UV output.  
         [0050]    As stated above, the outer periphery  58  of tube  52  includes first region  60  and second region  70  having lengths L 2  and L 3 , respectively. The first region  60  has a continuous helical groove path that defines a series of axially spaced apart grooves  62  formed therein, each having a width of W 1 . It should be noted that although in the embodiment shown herein, the groove path is continuous, it is envisioned that the groove path can be discontinuous. Grooves  62  have an axial spacing P 1  and are formed in a plane which intersects axis  66  at an acute angle. Due to the presence of grooves  62 , a portion of the arc stream which extends between the axially opposed electrodes tends to travel in a generally sinusoidal path in first region  60 . As a result, the arc stream length in this region is increased without increasing the length L 2  of first region  60 . In addition, due to the restriction caused by grooves  62 , in this region, the arc stream travels closer to the periphery  58  of tube  52 . Each of the foregoing physical properties and conditions advantageously serves to improve the recombination rate of the mercury ions with the phosphor coating  56 . Consequently, the intensity of the ultraviolet radiation in first region  60  is increased and is therefore higher than the UV intensity in second region  70  (all other variables being equal).  
         [0051]    An exemplary embodiment of tube  52  further includes reflective coating  68  which is adapted and configured to direct the ultraviolet radiation in the substantially downward direction, e.g., through aperture  69 . Reflective coating  68  is positioned adjacent to interior surface  57  and is radially outward of phosphor coating  56  and extends over a portion of the circumference of interior surface  57 . Preferably reflective coating  68  extends over approximately 300 degrees of the circumference. In the embodiment shown in FIG. 3 a,  reflective coating  68  extends axially over length L 2 . In addition to directing the ultraviolet radiation in a substantially downward direction, reflective coating  68  aids in focusing the UV radiation generated in first region  60  over the facial region. More particularly, the reflective coating  68  generally reduces the amount of refraction which normally occurs due to the vitreous tube  52  and causes the radiant energy to be axially dispersed.  
         [0052]    It should be noted that the shape (e.g., width), size (e.g., depth), spacing and orientation (e.g., angle) of the grooves can be selectively adjusted in order to achieve a desired intensity within a region. For example, by increasing the depth of grooves  62 , thereby bringing the arc stream closer to periphery  58 , the intensity in first region  60  is further increased. Also, by orienting the grooves  62  at an angle with respect to axis  66 , a larger portion of periphery  58  is deformed than is deformed when the grooves are formed in a plane perpendicular to axis  66 . Additionally, when the grooves  62  are angled, the cross-section of periphery  58  is non-circular in the groove locations. The presence of a larger amount of deformed surface area and the non-circular cross-section each further increases the arc stream length and the plasma recombination efficiency adjacent to the phosphor.  
         [0053]    As clearly illustrated above, the formation of grooves  62  in first region  60  of tube  52  enables discharge lamp  50  to provide two distinct and predetermined regions of UV intensity. Additionally, through the adjustment of parameters such as the groove depth, spacing, orientation and width, the intensity of the UV radiation emitted from the first region  60  can be selectively established and/or controlled, both from an absolute sense and on a relative basis as compared to an adjacent region that is devoid of such grooves.  
         [0054]    More specifically, by adjusting any one or a combination of the above-identified parameters, the desired UV output of first region  60  of lamp  50  can be achieved. It should also be noted that, although the first region  60  is shown in FIG. 3 a  to be positioned adjacent to first end seal  54   a,  which is preferable for a tanning application, this region can be positioned anywhere along the length of tube  52 . In some applications, for example, it may be desired to have a region of higher intensity located at the center of the tube  52 .  
         [0055]    Referring now to FIGS. 4 a  and  4   b,  there is illustrated an alternate embodiment of the subject discharge lamp designated generally as reference numeral  150 . Structural elements of the embodiment shown herein which are similar to those disclosed with respect to the exemplary embodiment of FIGS. 3 a - 3   c  are identified by similar reference numerals. As before, discharge lamp  150  includes an elongated vitreous tube  152 , first and second end seals  154   a  and  154   b,  and first and second electrodes (not shown). Tube  152  has a phosphor coating  156  applied to interior surface  157  and has a drop of mercury disposed within central core  153 . Tube  152  has an outer periphery  158  which extends axially between the first and second end seals  154   a  and  154   b.  The overall length of tube  152  is identified as L 1 .  
         [0056]    Tube  152  also includes a first region  160  and second region  170 , each extending axially along length L 1  of lamp  150 . The lengths of the first and second regions  160  and  170  are identified as L 2  and L 3  respectively. However, unlike second region  70  of discharge lamp  50 , second region  170  of lamp  150  includes axially spaced apart grooves  172 . Grooves  172  have an axial spacing P 2  and are oriented at an acute angle with respect to axis  166 . The spacing P 2  and orientation of grooves  172  are different than the spacing P 1  and the orientation of grooves  162  within first region  160 . As a result, the UV intensity within second region  170  is different than that emitted from first region  160 . It should be noted that FIG. 4 a  illustrates how two regions of varying intensity can be defined by varying the groove spacing and angular orientation. It should be further noted that the two distinct regions could be defined by varying the groove depth, spacing, orientation and width or combinations thereof. Also, in the embodiment shown in FIG. 4 a,  the groove spacing and orientation of first region  160  is such that higher intensity UV emission will be present in this region. Alternatively, the groove parameters can be adjusted such that second region  170  has a higher intensity emission if desired for a specific application. Although in the embodiment shown herein, the groove path is continuous, it is envisioned that the groove path can be discontinuous.  
         [0057]    Referring now to FIGS. 5 a  and  5   b,  there is illustrated yet another exemplary embodiment of a discharge lamp according to the present disclosure, designated generally as reference numeral  250 . Structural elements of the embodiment shown herein which are similar to those disclosed with respect to the exemplary embodiment of FIGS. 3 a - 3   c  are identified by similar reference numerals. As before, discharge lamp  250  includes an elongated vitreous tube  252 , first and second end seals  254   a  and  254   b,  and first and second electrodes (not shown). Tube  252  has a phosphor coating  256  applied to interior surface  257  and has a drop of mercury disposed within central core  253 . Tube  252  has an outer periphery  258  which extends axially between the first and second end seals  254   a  and  254   b.  The overall length of tube  252  is identified as L 1 .  
         [0058]    Unlike tube  52  of lamp  50 , tube  252  includes a first region  260 , a second region  270 , and a third region  280 , each axially arranged or deployed along length L 1  of lamp  250 . The lengths of the first, second and third regions  260 ,  270  and  280  are identified as L 2 , L 3  and L 4 , respectively. In the embodiment disclosed herein, second region  270  and third region  280  of lamp  250  include axially spaced apart grooves  272  and  282 , respectively. Grooves  272  and  282  have an axial spacing of P 2  and P 3  respectively and are both oriented at an acute angle with respect to axis  266 . However, the angular orientation of grooves  272  is greater than that of grooves  282 . Since the spacing and orientation of the grooves within the first, second and third regions differ, the UV intensity emitted from these regions differ. It should be noted that FIG. 5 a  illustrates how three regions of varying intensity can be defined by varying the groove spacing and angular orientation. As stated before, the distinct regions can be defined by varying the groove depth, spacing, orientation and width or combinations thereof. It should be noted that although in the embodiment shown herein, the groove path is continuous, it is envisioned that the groove path can be discontinuous.  
         [0059]    Referring now to FIGS. 6 a - 6   c,  there is illustrated a further exemplary lamp  350  according to the present disclosure which is structurally similar to lamps  50 ,  150  &amp;  250  and is adapted and configured for use in tanning chamber  100  of FIG. 1. Similar to the previously described embodiments, lamp  350  includes an elongated vitreous tube  352 , first and second end seals  354   a  and  354   b,  and first and second electrodes (not shown). Tube  352  has a phosphor coating  356  applied to interior surface  357  and has a drop of mercury disposed within central core  353 . An outer periphery  358  of tube  352  extends axially between the first and second end seals  354   a  and  354   b.    
         [0060]    In contrast to the previously described tubes, namely tubes  52 ,  152  and  252 , the outer periphery  358  of tube  352  is not segmented into multiple regions, e.g., first and second regions having lengths L 2  and L 3 , respectively. Outer periphery  358  of tube  352  has a plurality of grooves  362  defined therein which are equally spaced and oriented and positioned along a helical path. The helical path extends axially along substantially the entire length L 1  of tube  352 , i.e., the helical path extends all the way to, or in close juxtaposition with, end seals  354   a,    354   b.  In the embodiment illustrated in FIG. 6 a,  the plurality of grooves  362  are interconnected and the helical path is continuous. Alternatively, the grooves  362  can be axially spaced apart and the helical path can be discontinuous.  
         [0061]    Each groove  362  has a width of W 1 , a depth of d 1 , and an axial spacing or pitch P 1 . As a result of the being defined along an axially extending helical path, each groove is formed in a plane which intersects axis  366  at an acute angle α. In the representative embodiment shown herein, tube  352  has an outer diameter D 1  of 1.5″ and the grooves  362  have an axial spacing or pitch P 1  of 9.0″, a depth d 1  of 0.125″ and a width W 1  of 0.50″. Based on the foregoing diameter and pitch, the ratio of pitch over d 1  is 72 (in/in). Also, the resulting ratio of the groove pitch to groove width is about 18 (in/in).  
         [0062]    As before, due to the presence of grooves  362 , a portion of the arc stream which extends between the axially opposed electrodes tends to travel in a generally sinusoidal path along the length of the tube. As a result, the arc stream length in this region is increased without increasing the overall length of the tube. In addition, due to the restriction caused by grooves  362 , the arc stream travels closer to the periphery  358  of tube  352 . Each of the foregoing physical properties and conditions advantageously serves to provide a lamp which emits ultraviolet radiation having properties and characteristics which are optimal for use in tanning applications. The grooves  362  also function to improve the efficiency of the lamp  350  and result in an operational cost savings when compared to lamps which have an unaltered outer periphery.  
         [0063]    The exemplary embodiment of tube  352  further includes reflective coating  368  which is adapted and configured to direct the ultraviolet radiation in the substantially downward direction, e.g., through aperture  369 . Reflective coating  368  is positioned adjacent to interior surface  357  and is radially outward of phosphor coating  356  and extends over a portion of the circumference of interior surface  357 . It should be noted that although phosphor coating  356  is shown as a single coating layer, phosphor coating  356  can be applied as a multiple coating, a mixture of phosphors or combinations thereof.  
         [0064]    Referring now to FIGS. 7 and 8 there is illustrated two alternate embodiments of the present discharge lamp which are designated by reference numerals  450  and  550  respectively. Similar to lamp  350 , lamps  450  and  550  have an outer periphery which has a plurality of grooves formed therein and positioned along a helical path that extends axially along approximately the entire length L 1  of the lamp. However, in contrast to lamp  350 , the groove width W 1 , depth d 1 , and pitch P 1  have been modified to provide alternate embodiments of the improved tanning lamp of the present disclosure.  
         [0065]    Through experimentation it has been determined that the following characteristics provide optimal overall performance for grooved tanning lamps:  
         [0066]    d 1  between about 0.100 inch to about 0.250 inch  
         [0067]    a ratio of groove pitch to groove depth of about between 8 (in/in) to about 120 (in/in)  
         [0068]    W 1  between about 0.250 inch to 1.0 inch and a ratio of groove pitch to groove width of about between 2 (in/in) to about 48 (in/in)  
         [0069]    a groove depth not exceeding 10 percent of the outside diameter of the tube  
         [0070]    Lamps configured to have the above identified groove properties, provide a UV radiation source for tanning applications which is aesthetically pleasing, stronger and more efficient than prior art lamps, in addition to satisfying all FDA regulations applied to tanning lamps.  
         [0071]    It is not intended that the present disclosure be limited to lamps having the above-identified characteristics. However, lamps having represent characteristics presently preferred, representative configurations and yield advantageous results for tanning applications.  
         [0072]    While exemplary discharge lamps have been described with respect to various specific embodiments, those of ordinary skill in the art will readily appreciate that various modifications, changes, and enhancements may be made thereto without departing from the spirit and scope of the invention as defined by the appended claims.