Abstract:
A UV light utilizing an angled dichroic cold mirror reflector to selectively direct UV light out of a window on the side of the light housing while transmitting visible and infrared light out a window in the end of the housing to eliminate heat. The light may be used both as a flashlight and a black light for UV inspection. A removable cap can be placed over the end window to block visible light.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This patent application claims benefit of U.S. provisional Serial No. 60/188,958, filed Mar. 13, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention concerns ultraviolet (UV or black) lights of a type used by technicians in carrying out leak detection inspections by illuminating potential leak sites to detect the presence fluorescent tracer dyes. This is commonly done in servicing air conditioning refrigeration systems, automobile air conditioning systems components, hydraulic machinery, etc. 
     The dyes are typically mixed with a compatible oil and injected into the system. If leaks are present, a trace of the dye and oil mixture flow onto external surfaces. This leakage fluoresces when illuminated with UV and sometimes blue light, emitting visible light which can be seen by the technician. 
     Such UV lights particularly adapted for leak detection service applications have been developed in recent years, utilizing selective reflection filters, sometimes referred to as “dichroic” filters which transmit ultraviolet wavelengths and reflect back visible light to maximize the user&#39;s ability to see any fluorescence that occurs. Such lights require high wattage lamps as a UV source as compared with most other application of UV lights, which therefore emit considerable heat energy. The use of reflecting or “dichroic” filters is a significant improvement over absorbent filters used in the past selectively which absorbed visible light from the high intensity light emitted by the lamps, since the filters themselves overheated if the light was used for long periods and sometimes cracked during such use. 
     For this reason, the dichroic filters have been designed to transmit infrared radiation as well as UV to prevent overheating of the dichroic filter and other components. This is described in copending U.S. application Ser. No. 08/964,839, filed on Nov. 5, 1997 and U.S. Pat. No. 5,905,268. In those lights, visible light is reflected back into the housing such that some heating of the interior of the light occurs. 
     In another types of testing, dyed smoke is used to initially locate leak, requiring a flashlight to detect the smoke. Also, it is often useful to have a flashlight available in darkened locations in buildings where equipment is being serviced. The previously UV lights have not been able to be used as an ordinary flashlight. 
     Accordingly, it is the object of the present invention to provide a UV light which while utilizing a high intensity lamp as a powerful source of UV light does not result in overheating of the light nor specifically the optical components eliminating visible light, and which emits a very high proportion of the UV light generated by the lamp. 
     It is another object to provide such a UV light which is also conveniently useable as a flashlight. 
     SUMMARY OF THE INVENTION 
     The above objects as well as others which will become apparent upon a reading of the following specification and claims are achieved by using a reflector rather than a dichroic filter to selectively act to produce a beam of UV light while also directing the visible and IR radiation out from the light. 
     The reflector selectively reflects only emitted UV light by the lamp, while transmitting visible and IR radiation. Such dichroic reflector is commonly known in the art as a “cold mirror”. The cold mirror reflector is angled with respect to the high wattage lamp so that the UV light beam is directed out of a light housing through a first window formed on one side of the light. 
     On the other hand, visible and infrared light is transmitted through the cold mirror reflector and out from a second window in the front end of the light housing. 
     A detachable cap may be secured over the second housing wind to optionally block the visible-infrared light beam from exiting the light housing. 
     Heating of the cold mirror reflector is minimized as none of the wavelengths are absorbed by that optical element, nor is retained elsewhere within the light housing when the cap is removed. 
     At the same time, the light is capable of a dual use, i.e., as a pure UV light source and also as a flashlight increasing its utility to the user, particularly where tracer smoke testing is to be practiced. 
     The light according to the invention is also compact and may be manufactured at low cost. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective exterior view of an embodiment of a light according to the invention. 
     FIG. 2 is a partially sectional view taken through the light shown in FIG.  1 . 
     FIG. 3 is a top view of the partial section of FIG.  2 . 
     FIG. 4 is a partially sectional view taken through the center of the light showing the reflector mounting. 
     FIG. 5 is an enlarged partially sectional view of the head portion of an alternate embodiment of the invention. 
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, certain specific terminology will be employed for the sake of clarity and a particular embodiment described in accordance with the requirements of 35 USC 112, but it is to be understood that the same is not intended to be limiting and should not be so construed inasmuch as the invention is capable of taking many forms and variations within the scope of the appended claims. 
     Referring to the drawings, and in particular FIG. 1, the UV light  10  according to the present invention includes a housing  11  comprised of an elongated handle  12  and head portion  14  both made of a suitable molded plastic. 
     A UV light beam window  16  faces to one side of the light  10 , while a visible-infrared window facing the end of light  10  is shown covered with a plastic cap  18 . 
     FIG. 2 shows the inner details of the UV light  10 . A 12 volt 100 watt lamp  20  which is a powerful source of UV and visible radiation of a much greater power than the type used with a standard flashlight. The lamp  20  may be of the Xenon type of high color temperature (3500K) which produces substantial long wave ultraviolet emissions. The envelop is made of quartz which is itself highly transmittive to long wavelength ultraviolet, i.e., 340-380 nm. Such a lamp is available from Osram Sylvania under part number FCR 64625 HLX. 
     The lamp  20  is located at the approximate focal point of a parabolic reflector  30 , electroformed of nickel on an accurately shaped stainless steel mandrel. A focal length of 0.187 inches allows the lamp  20  to be approximately located at the focal point to maximize beam concentration. 
     As described in copending U.S. application Ser. No. 09/491,413, filed on Jan. 26, 2000 and U.S. application Ser. No. 08/964,839, filed on Nov. 5, 1997, the parabolic reflector  30  is preferably coated to eliminate destructive interference which would reduce the intensity of the reflected UV light 
     The surface of the parabolic reflector  30  has a plurality of coatings applied thereto, one of aluminum and one of silicon dioxide. The interface of silicon dioxide and air, and silicon dioxide and aluminum produces a double refraction in an opposite sense, which offset each other to eliminate the potential destructive interference which otherwise could occur. 
     The first coating is of aluminum, while the second coating is of silicon dioxide. The thickness of the silicon dioxide should be uniform and accurately held to achieve this effect, the thicknesses determined by the “quarter wave stack” principle. 
     The refractive index of each interface, i.e., the silicon dioxide and air, silicon dioxide and aluminum determines the effective phase shift of the reflected light. A thickness of aluminum of 0.057 microns and of silicon dioxide of 0.066 microns has been successfully used for this purpose. The silicon dioxide-air interface causes an approximate 13 degree forward phase shift, the silicon dioxide-aluminum interface a 13 degree lagging phase shift, thereby offsetting each other. 
     Silicon dioxide coatings have heretofore been employed simply to protect the substrate from scratches and oxidation but have not been sufficiently uniform nor of the proper thickness to achieve enhanced reflection of ultraviolet wavelengths. 
     A coated parabolic reflector  30  suitable for this use is available from American Galvano, 312 N. Cota St., Unit I, Corona, Calif. 91720. 
     The lamp  20  can be powered from a 12 volt power source such as a vehicle cigarette lighter socket by use of a plug connector  24  connected by cables  26 , a strain fitting  28  at the entrance to the handle  12 . An on-off switch  33  connects one lead to the lamp  20 , a connector  32  connecting the other lead. Batteries or an AC power source can also be used. 
     A selective dicbroic reflector  36  is mounted within the head portion  14  opposite the reflector  30  and lamp  20 , inclined at 45° such as to redirect UV light emitted from the lamp  20  and parabolic reflector  30  out through the window  16  in one side of the housing  11 . The selective reflector  36  acts as a beam splitter, transmitting visible and infrared light while reflecting UV light such as to direct a pure UV beam out through the lens window  16 . The window  16  may be covered with a window lens constructed of borosilicate glass which is believed to block shorter wavelengths of UV light which might be hazardous to the eyes, i.e., around 320 nm and lower. 
     The cold mirror reflector  36  preferably is of dichroic design utilizing a series of coatings of a predetermined thickness to create selective reflection. This invention contemplates a design of such coatings to produce selective reflection of UV light rather than transmission of UV light as described in U.S. Pat. No. 5,905,268, so that a UV light beam is directed out through the side facing window  16 . 
     At the same time, the coatings are designed so that visible light is transmitted through the reflector  36  rather than reflected, so that a beam of visible light is directed out through the window  38  covered by cap  18 . Window  38  is also preferably covered with a clear lens covering constructed of borosilicate glass to block any deep UV light. 
     As disclosed in U.S. Ser. No. 09/491,413, filed on Jan. 26, 2000, dichroic optical elements from ZC &amp; R Coatings for Optics, Inc. of Torrance, Calif. are preferred as having coatings of tantalum pentoxide which do not absorb UV. 
     A suitable cold mirror having a part number CM-UV-350 is commercially available from ZC &amp; R. 
     That particular cold mirror has a high percentage of reflectance and low percentage of transmittance of wavelength in the range of 350 nm to 450 and a high percentage of transmittance of wavelength from 600 nm to 1200 nm and higher. Deep UV, i.e., below 340 nm is largely transmitted. 
     Thus, both visible and infrared are caused to be transmitted out of the light  10  to minimize heating and to create a visible beam for use in other tests and as a flashlight. 
     The coatings of the cold mirror reflector  36  can also be applied by ZC &amp; R to minimize blue visible light at wavelengths over 400 nm where the tracer dyes do not fluorescence in response to such blue light in order to eliminate the need for “blue blocker” eyeglasses which are necessary when the UV light beam also contains blue light. 
     Elimination of blue light in the UV beam is advantageous for some leak testing applications as described in the above referenced copending application. 
     The cold mirror reflector  36  can comprise a rectangular piece of coated borosilicate glass as seen in FIGS. 3 and 4. A molded-in groove  40  holds the reflector  36  in position in the head  14  at a 45° angle. 
     The cap  18  also of a molded plastic such as silicone can be opaque to block the visible light, or the cap  18  can be removed to use the light  10  as a flashlight. If the visible light does not interfere with observation of the fluorescence, since being directed at 90° to the UV beam, the cap can be removed, tab  42  assisting in its removal, to maximize cooling of the housing interior. 
     Alternatively, as shown in FIG. 5, the head  14 A can be formed with forward facing louvers  44  which shield vent openings  46  to improve cooling with the cap  18  in place.