Abstract:
The present disclosure provides a device and method for exposing a substrate to ultraviolet radiation emitted from a discharge lamp having regions of varying intensity along its length. 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 elongated vitreous tube has 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 regions defined along said axial length, wherein a first region extends over a predetermined first portion of said axial length and has a helical groove path defining a series of axially spaced apart grooves formed therein. The first region emits ultraviolet radiation having an intensity greater than that emitted from a second region of the outer periphery.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to discharge lamps, and more particularly, to a discharge lamp for use in applications such as tanning, wherein the lamp includes a vitreous tube having a series of grooves formed in its periphery so as to create regions of varying ultraviolet radiation intensity along its length. 
     2. Background of the Related Art 
     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. 
     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 are 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. 
     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. 
     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). 
     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. 
     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. 
     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, the proper combined UV exposure operates to create a light-protection mechanism. 
     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. 
     U.S. Pat. No. 5,557,112 to Csoknyai et al. discloses a fluorescent lamp having 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. 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. 
     The patent literature also includes disclosures concerning tubular lamp assemblies that include constricted portions or grooves. See e.g., U.S. Pat. No. 2,916,645 to Lemmers et al.; U.S. Pat. No. 3,129,085 to Olsen et al.; U.S. Pat. No. 4,825,125 to Lagushenko et al; U.S. Pat. No. 3,988,633 to Shugan et al.; and Des. Pat. No. 198,268. The prior art patent disclosures also teach conventional systems and processes for forming such constricted portions and/or grooves in tubular lamps. 
     There is a need therefore, for a discharge lamp for use in applications such as tanning, wherein a single discharge lamp has multiple regions of varying ultraviolet radiation intensity along its length. 
     SUMMARY OF THE INVENTION 
     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. The outer periphery has a plurality of regions defined along said axial length, wherein a first region extends over a predetermined first portion of said axial length and has a helical groove path which defines a series of axially spaced apart grooves. 
     In a preferred embodiment, the helical groove path is continuous. Alternatively, the helical groove path is discontinuous. The grooves may be formed using conventional technologies, as is known in the art. It is envisioned that the grooves of the first region are formed in a plane which intersects the axis of the tube at an acute angle. Preferably, the first region has a length of about approximately 18 inches and the length of the vitreous tube is approximately 72 inches. 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. 
     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. The coating on an interior of the vitreous tube is applied along the entire length and emits ultraviolet radiation when a voltage is applied across the first and second electrodes. The first region emits ultraviolet radiation having an intensity greater than emitted from a second region of the outer periphery. It is presently preferred that the coating is a phosphor coating. 
     In an exemplary embodiment, the discharge lamp further includes a reflective coating on the interior of the vitreous tube and disposed between the coating and the vitreous tube wall, the reflective coating extending about a portion of the vitreous tube circumference. It is also envisioned that in a presently preferred embodiment, the reflective coating extends exclusively over the first region. Alternatively, the reflective coating extends over the entire length of the tube. 
     In an alternate embodiment of the subject disclosure, the second region of the outer periphery has a second helical path that defines a second series of axially spaced apart grooves. The grooves formed in the second region of the outer periphery can have a groove depth which is less than a depth of the grooves formed in the first region. Alternatively, the grooves formed in the second region of the outer periphery can have an axial spacing which is greater than the axial spacing of the grooves formed in the first region. Still further in the alternative, the grooves formed in the second region of the outer periphery can be formed in a plane which intersects the tube axis at an angle which is less than the angle of intersection of grooves in the first region. 
     The outer periphery of the discharge lamp of the present disclosure can further include a third region. The third region of the outer periphery can define a third helical groove path that forms a third series of axially spaced apart grooves. 
     The present disclosure is also directed to a discharge lamp for use in tanning applications which includes, inter alia, an elongated vitreous tube, first and second electrode assemblies, and a coating on the interior of the tube. 
     The elongated vitreous tube has an outer periphery and axially opposed first and second ends which define a length for the tube therebetween. The outer periphery has at least first and second regions defined along said axial length. Wherein the first region extends over a predetermined first portion of said axial length and has a helical groove path which defines a series of axially spaced apart grooves and emits radiation having an intensity greater than that emitted from the second region. 
     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. The coating is applied on an interior of the vitreous tube along the entire length for emitting ultraviolet radiation when a voltage is applied across the first and second electrodes; 
     The present disclosure is also directed to a method of exposing a substrate to ultraviolet radiation of varying intensity. The method includes the steps of providing a substrate to be exposed; positioning a discharge lamp assembly in proximity to the substrate; and exposing the substrate to the ultraviolet radiation emitted from the lamp. 
     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 elongated vitreous tube has 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 regions defined along said axial length, wherein a first region extends over a predetermined first portion of said axial length and has a helical groove path defining a series of axially spaced apart grooves. 
     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. The coating on an interior of the vitreous tube is applied along the entire length and emits ultraviolet radiation when a voltage is applied across the first and second electrodes. The first region emits ultraviolet radiation having an intensity greater than emitted from a second region of the outer periphery. It is presently preferred that the coating is a phosphor coating. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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: 
     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; 
     FIG. 2 illustrates a sectional view of the tanning chamber of FIG. 1 taken along line  2 — 2 ; 
     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; 
     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; 
     FIG. 3 c  illustrates an exploded cross-sectional view of the area identified as  3   c  in FIG. 3 a;    
     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; 
     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; 
     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; and 
     FIG. 5 b  is a cross-sectional view of the discharge lamp of FIG. 5 a  taken along line  5   b — 5   b.   
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     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. 
     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 . 
     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. 
     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. 
     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 with 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. 
     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. 
     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. 
     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). 
     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 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. 
     It should be noted that the shape (width), size (depth), spacing and orientation (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. 
     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. 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 . 
     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 . 
     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. 
     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 . 
     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. 
     While exemplary discharge lamps having multiple intensity regions 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.