Abstract:
A linear light-emitting diode (LED)-based solid-state device comprising a curved surface to hold a flexible printed circuit board with multiple linear arrays of surface mount LEDs provides lighting applications with a broad viewing angle over 180° along the radial direction. On each of the two lamp bases of the lamp, a shock-protection switch is mounted to prevent shock hazard during re-lamping.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to linear light-emitting diode (LED) lamps and more particularly to a linear LED lamp with a curved surface to provide a broad viewing angle over 180° along the radial direction. 
         [0003]    2. Description of the Related Art 
         [0004]    Solid-state lighting from semiconductor light-emitting diodes (LEDs) has received much attention in general lighting applications today. Because of its potential for more energy savings, better environmental protection (more eco-friendly, no mercury used, and no UV and infrared light emission), higher efficiency, smaller size, and much longer lifetime than conventional incandescent bulbs and fluorescent tubes, the LED-based solid-state lighting will be a mainstream for general lighting in the near future. Meanwhile, as LED technologies develop with the drive for energy efficiency and clean technologies worldwide, more families and organizations will adopt LED lighting for their illumination applications. In this trend, the potential safety concerns such as risk of electric shock need to be well addressed. 
         [0005]    In many applications of commercial and residential lighting, a linear LED-tube (LLT) lamp is used to replace an existing fluorescent tube, taking advantages of the above said LED&#39;s features. In a lighting application of a refrigerated warehouse, an LLT lamp is used to replace a fluorescent lamp because the latter cannot operate at a low temperature of minus 20 degrees Celsius. Use of a high intensity discharge (HID) lamp instead creates much heat and causes the cooling system in the refrigerated warehouse to consume more energy to cool down the refrigerated area. LEDs, however, can operate at minus 40 degrees Celsius, do not generate heat, and thus are well suited for this application. Typical energy savings due to the reduced lighting load are 40%-60% with an additional 12%-19% savings from reduced cooling load. 
         [0006]    In high-ceiling lighting applications such as in offices, manufacturing areas, warehouses, showcases in department stores, etc, LLT lamps are used to take advantage of the lowest maintenance cost and the lowest power consumptions and heat dissipations among all kinds of lighting. An LLT lamp can save energy and operating cost by 70%. 
         [0007]    A surface mount device (SMD) LED, as a Lambertian emitter, can provide only a beam angle of 120°, in principle. A linear LED tube (LLT) lamp based on surface mount technology inherits this limitation. In some applications such as above mentioned high ceiling areas and refrigerated warehouses, the viewing angle of 180° is required. Some manufacturers, therefore, provide LLT lamps with multiple user-specifiable viewing angles to meet this market demand. They use a variable angle-mounting bracket or rotatable end caps adjusting illumination angle up to 180°. To help install fixtures accurately, they even provide clear bracket featuring angle indicators. Other manufacturers use linear parabolic reflectors and thin-film diffusers to create various beam angles. However, measures such as optics and other means than the present invention can provide only a solution at the expense of extra energy loss due to a limitation of optical efficiency such as transmission, reflection, and absorption loss. 
         [0008]    To deal with a wide illumination angle, Timmermans et al. suggests in their patent (U.S. Pat. No. 7,049,761 B2) that a circuit board with an H-shaped cross-section be used. On the horizontal plane of the “H” (horizontal bar in H, extended along the direction to the paper), a plurality of dual-in-line (DIP) LEDs are mounted with different viewing angles against each adjacent one. Because the circuit board that supports LEDs is flat on that plane, the mounting planes for LEDs with different coverage angles must be different to produce an overall predetermined radiation pattern. The DIP LEDs used have a viewing angle between 6° and 45°. For an overall 180° viewing angle, the mounting plane must be between 67.5° and 87° relative to the original plane. One of drawbacks for this design is poor manufacturability, not only in drilling holes at those large oblique angles from the plane normal for mounting DIP LEDs but also in making soldering for each LED connection. Strictly speaking, such drilling at oblique angles between 67.5° and 87° is not manufacturing feasible. Moreover, individual soldering for hundreds of LEDs presents a low-yield, not mentioning inefficiency. 
         [0009]    In retrofit application of a linear LED tube (LLT) lamp to replace an existing fluorescent tube, one must remove the starter or ballast because the LLT lamp does not need a high voltage to ionize the gases inside the gas-filled fluorescent tube before sustaining continuous lighting. LLT lamps operating at AC mains, such as 110, 220, and 277VAC, have one construction issue related to product safety and needed to be resolved prior to wide field deployment. This kind of LLT lamps always fails a safety test, which measures through lamp leakage current. Because the line and the neutral of the AC main apply to both opposite ends of the tube when connected, the measurement of current leakage from one end to the other consistently results in a substantial current flow, which may present risk of shock during re-lamping. Due to this potential shock risk to the person who replaces LLT lamps in an existing fluorescent tube fixture, Underwriters Laboratories (UL), use its standard, UL 935, Risk of Shock During Relamping (Through Lamp), to do the current leakage test and to determine if LLT lamps under test meet the consumer safety requirement. 
         [0010]    An LLT lamp is at least 2 feet long; it is very difficult for a person to insert the two opposite bi-pins at the two ends of the LLT lamp into the two opposite sockets at two sides of the fixture at the same time. Because protecting consumers from possible electric shock during re-lamping is a high priority for LLT lamp manufacturers, they need to provide a basic protection design strictly meeting the minimum leakage current requirement and to prevent any possible electric shock that users may encounter in actual usage. In other words, when shock hazard happens, the manufacturers have no excuses to claim that they do have proper procedures mentioned in their installation instructions. 
         [0011]    Referring to  FIG. 1 , a conventional LLT lamp  100  comprises a plastic housing  110  with a length much greater than its radius of 30 to 32 mm, two end caps  120  and  130  each with a bi-pin  180  and  190  on two opposite ends of the plastic housing  110 , LED arrays  140  and  141  mounted on two PCBs  150  and  151 , electrically connected in series using a connector  145 , and an LED driver used to generate a proper DC voltage and provide a proper current from the AC main and to supply to the LED arrays  140  and  141  such that the LEDs  170  and  171  on the two PCBs  150  and  151  can emit light. In some conventional LLT lamps, DIP rather than SMD LEDs are used as lighting sources. Although SMD LEDs and the supporting PCB allow more efficient manufacturing, higher yield, higher lumen output and efficacy, and longer life than their DIP counterparts do, some LLT lamp providers still produce such DIP-based products. The two PCBs  150  and  151  are glued on a top plane of the lamp using an adhesive with its normal parallel to the illumination direction. In this case, the viewing angle of the LLT lamp is limited by that of individual LEDs. While SMD LEDs used in the LLT lamp provide a viewing angle less than 120° due to Lambertian emission, a DIP-based LLT lamp offers much less viewing angles. 
         [0012]    The bi-pins  180  and  190  on the two end caps  120  and  130  connect electrically to an AC main, either 110 V, 220 V, or 277 VAC through two electrical sockets located lengthways in an existing fluorescent tube fixture. The two sockets in the fixture connect electrically to the line and the neutral wire of the AC main, respectively. The LLT lamp  100  may present electric shock hazard when one of the bi-pins  180  or  190  is first inserted into the socket that connects to the line of AC main. The energized LED driver causes a lamp leakage current flowing through the exposed bi-pin  190  or  180  not in the socket, and thus presents risk of shock during re-lamping. 
         [0013]      FIG. 2  is an illustration of another conventional LLT lamp, claiming to have a wider viewing angle. The LLT lamp  1000  comprises a plastic housing  1100  as bulb portion, and an “H” shape circuit board  1200 . On the horizontal plane  1300  of “H” is DIP LEDs  1301  mounted. DIP LEDs  1401  and  1501  are mounted on different planes  1400  and  1500 , respectively (shown in  FIG. 3 ). No end caps with bi-pin are shown in  FIG. 2  for clarity.  FIG. 3  is a cross-sectional view of  FIG. 2 . The LED array  1301  is mounted on the plane  1300  while LED arrays  1401  and  1501  are mounted on the plane  1400  and  1500 , respectively, each with their own radiation patterns. In combination, the overall beam has a wider viewing angle in the radial direction than the individual beam does. As mentioned, when the planes  1400  and  1500  incline at large angles to achieve an 180° viewing angle for the overall beam emitted from DIP LEDs, the hole drilling at such oblique angles as 67.5° and 87° relative to the original plane  1300  becomes manufacturing infeasible. As can be seen, the beam angle is far from 180°, partly because the two vertical planes  1600  and  1601  of “H” block part of the beam. DIP rather than SMD LEDs used are another reason that the beam cannot radiate that wide due to the limitation of narrow viewing angle of DIP LEDs. 
       SUMMARY OF THE INVENTION 
       [0014]    A conventional linear surface mount device (SMD) LED-based lamp can provide only a beam angle of 120° due to a limitation of Lambertian emitters. In many lighting applications, a wider beam angle in LLT radial direction is required. The present invention then provides a linear light-emitting diode (LED)-based solid-state device comprising a curved surface to hold a flexible printed circuit board (PCB) with multiple linear arrays of SMD LEDs for lighting applications of an 180° beam angle. The printed circuit board used is thin and flexible enough such that it can be tightly attached and glued on the curved surface. Each linear LED array on the PCB can then emit light at an angle determined by the radius of the curved surface and the distance between the LED array and the central line of the LED PCB along the length. In superposition, the LLT lamp can offer a beam angle over 180° along the radial direction, suited for wide-angle applications. The approach provides a means for mass production and eliminates any extra energy loss associated with limitations of optical efficiency such as transmission, reflection, and absorption loss of optics. 
         [0015]    Such LLT lamps can be used in such applications as high ceiling offices, store showcases, warehouses, task lighting for cabinets, kitchen closets, kitchens, small coves, and in indirect lighting applications or any other places where accent lighting is required. Other applications such as back lighting for square billboards or advertisement boards are also possible. 
         [0016]    To protect consumers from possible electric shock during re-lamping, the present invention provides two special lamp bases, one for each end of the LLT lamp. Each lamp base contains a standard bi-pin and at least one shock protection switch, both mounted on a lamp base PCB, rather than on an end cover. This structure is different from that of the conventional LLT lamp, which uses two end caps in which the bi-pins are directly mounted. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is an illustration of a conventional LLT lamp. 
           [0018]      FIG. 2  is an illustration of another conventional LLT lamp. 
           [0019]      FIG. 3  is a cross-sectional view of the LLT lamp in  FIG. 2 . 
           [0020]      FIG. 4  is a cross-sectional view of the LLT lamp according to the present invention when the LED driver, the lamp base, and associated shock protection switches are omitted. 
           [0021]      FIG. 5  is a perspective view of an LLT lamp according to the present invention. 
           [0022]      FIG. 6  is an illustration of a curved surface on top of the LLT housing according to the present invention. 
           [0023]      FIG. 7  is an illustration of a LED PCB curved to fit the curved surface of the housing according to the present invention. 
           [0024]      FIG. 8  is an illustration of an embodiment with a 197° viewing angle according to the present invention. 
           [0025]      FIG. 9  is an illustration of an LLT lamp with shock protection switches according to the present invention. 
           [0026]      FIG. 10  is an illustration of a lamp base with a shock protection switch in place according to the present invention. 
           [0027]      FIG. 11  is an illustration of a lamp base PCB assembly for the LLT lamp according to the present invention. 
           [0028]      FIG. 12  is an illustration of an end cover for the LLT lamp according to the present invention. 
           [0029]      FIG. 13  is a block diagram of an LLT lamp with shock protection switches according to the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]      FIG. 4  is a cross-sectional view of the LLT lamp according to the present invention when the LED driver, the lamp base, and associated shock protection switches are omitted. The LLT lamp  600  has a housing  610  with a curved surface  620  on the top. The housing  610 , preferably metallic in material, serves also as a heat sink with a toothed profile to increase the heat dispersion. Other types of projections can be formed on the outer surface of the housing for improved heat dispersion. On the top of the curved surface  620  is a thin and flexible single-piece LED PCB  630  curved to fit closely to the surface  620 . The LED PCB  630  electrically and mechanically supports the SMD LEDs  631 ,  632 , and  633 , arranged in arrays. Because the LED PCB  630  follows the curvature of the surface  620  when it tightly fits on the surface  620 , the SMD LEDs  631 ,  632 , and  633  on the LED PCB  630  then have different normal directions relative to the tangential planes at their positions. Supposed that the angle subtended between the normal direction of LED  631  and of LED  632  is 30°. Similarly, supposed that the angle subtended between the normal direction of LED  633  and of LED  632  is also 30°. While SMD LEDs have a half viewing angle of 60°, the overall light emission pattern from LEDs  631 ,  632 , and  633  covers the entire 180° in the radial direction. In the light emission direction, a lens  500  is used to further regulate the light emission pattern and to protect the LEDs from accidental damage. In the hollow space below the curved surface is a driver enclosure  410  for holding an LED driver that powers the LEDs  631 ,  632 , and  633 . Although a metallic housing  610  is preferred for more effectively dispersing heat, the present invention is not limited to one having a metallic housing. Namely, the LLT lamp in the present invention may have a non-metallic housing. 
         [0031]      FIG. 5  is a perspective view of an LLT lamp according to the present invention. The lamp comprises two lamp bases  260  (only one shown for clarity), one at each end of the housing  610  and each having a shock protection switch and a bi-pin  250 , LEDs  631 ,  632 , and  633 , an LED driver (not shown) inserted into the driver enclosure  410  (not shown in  FIG. 5 ), which is inserted into the hollow space  207 , and a lens  500  (not shown for clarity). On top of the housing  610  is the curved surface  620  on which a curved LED PCB  630  that follows closely the curvature of the curved surface  620  is mounted. 
         [0032]      FIG. 6  is illustrates the curved surface  620  of the LLT housing according to the present invention. On top of the housing  610  is the curved surface  620 , below which a hollow space  207  is shown. 
         [0033]      FIG. 7  is an illustration of a LED PCB curved to fit the curved surface of the housing. The LED PCB  630  is thin and flexible enough such that when it is attached to the curved surface  620 , it can follow the curvature of the surface  620 . Thus, each SMD LEDs  631 ,  632 , and  633  can emit light from a tangential plane at its position. In superposition, the LLT lamp offers an 180° beam angle along the radial direction, thus suitable for wide-angle applications. The SMD LEDs  631 ,  632 , and  633  can first be mass-soldered on the PCB  630 , taking advantage of surface mount technology. Then the PCB is attached and fixed on the curved surface  620  on the housing  610  such that it follows the curvature of the surface  620 .  FIG. 8  is an illustration of a 197° viewing angle according to the present invention. The subtended angle between the normal direction  801  of LED  631  and the normal direction  802  of LED  632  is determined by the radius of curvature of the curved surface  620  and the distance between LED  631  and LED  632 . Similarly, the subtended angle between the normal direction  803  of LED  633  and the normal direction  802  of LED  632  is determined by radius of curvature of the curved surface  620  and the distance between LED  633  and LED  632 . In  FIG. 8 , SMD LED arrays  631 ,  632 , and  633  have their individual half-viewing angle of 60°. In combination, the overall viewing angle reaches 197°. The LED PCB can be replaced by a semiconductor substrate with multiple LED chips built directly on the substrate—a process widely used to produce integrated circuit based on large-scale-integration (LSI) technology in semiconductor industry. Because no optics or other means than the curved surface that defines the emission pattern, the approach eliminates extra energy loss associated with limitations of optical efficiency such as transmission, reflection, and absorption loss of optics. 
         [0034]    The present invention uses also a shock-protection switch design on the two lamp bases to prevent electric shock from happening during re-lamping.  FIG. 9  is an illustration of an LLT lamp with a shock protection switch according to the present invention, with only one lamp base  260  shown. The relative positions of lamp bases  260 , a protection switch mechanism, and the lamp housing  610  are shown in  FIG. 9 , with more details given in  FIGS. 10 ,  11  and  12 .  FIG. 10  is an illustration of the lamp base  260 , which comprises a lamp base PCB assembly  230  ( FIG. 11 ) and an end cover  235  ( FIG. 12 ). In  FIG. 10 , the lamp base PCB assembly  230  further comprises a standard bi-pin  250  and one shock protection switch with actuation mechanism  240 , mounted on a PCB  231 . The PCB  231  has etched conductors in two layers. One layer is used to connect between the two pins of the bi-pin  250 . The other one is used to connect one of the two electrical contacts of the protection switch to the bi-pin  250  through the soldering point  232  using a wire connection.  FIG. 12  is an illustration of the end cover  235  for holding and fixing the lamp base PCB assembly  230  on an end of the LLT lamp  600 . When the lamp base  260  is fixed on the housing  610  through two counter-bore screw holes  242 , the bi-pin  250  and the switch actuation mechanism  240  will protrude from the holes  251  and  243 , respectively. The lamp base  260  uses the bi-pin  250  to connect the AC mains to the LED driver through the protection switch, normally in “off” state. When pressed, the actuation mechanism  240  actuates the switch and turns on the connection between the AC mains and the LED driver. 
         [0035]      FIG. 13  is a block diagram of an LLT lamp  600  with protection switches  210 / 310  in the present invention. As shown, the LED driver  400  and the LED arrays  214  are individual modules. The modular design allows LLT lamps  600  to be produced more effectively while more numbers of LEDs can be surface-mounted in the LED PCB  630  area that electronic components of the LED driver may otherwise occupy. The lamp using this design can provide a sufficiently high lumen output, thus improving the system efficacy required by Energy Star program. The shock protection switch  210  (as dash circle) comprises two electrical contacts  220  and  221  and one actuation mechanism  240 . Similarly, a shock protection switch  310  (as dash circle) comprises two electrical contacts  320  and  321  and one actuation mechanism  340 . 
         [0036]    The shock protection switch can be of a contact type (such as a snap switch, a push-button switch, or a micro switch) or of a non-contact type (such as electro-mechanical, magnetic, optical, electro-optic, fiber-optic, infrared, or wireless based). The proximity control or sensing range of the non-contact type protection switch is normally up to 8 mm. 
         [0037]    Referring to  FIG. 13 , one of the contacts  220  connects electrically to the bi-pin  250  in the lamp base  260  that connects to AC mains, and the other contact  221  connects to one of the inputs  270  of the LED driver  400 . One of the contacts  320  connects electrically to the bi-pin  350  in the lamp base  360  that connects to AC mains, and the other contact  321  connects to the other input  370  of the LED driver  400 . The switch is normally off. Only after actuated, will the switch turn “on” such that it connects the AC mains to the LED driver  400  that in turn powers the LED arrays  214 . Served as gate controllers between the AC mains and the LED driver  400 , the protection switch  210  and  310  connect the line and the neutral of the AC mains to the two inputs  270  and  370  of the driver  400 , respectively. The protection switch may have direct actuation or sensing mechanism that actuates the switch function. 
         [0038]    Referring to  FIGS. 9 and 13 , if only one shock protection switch  210  is used at one lamp base  260  for one end of the LLT lamp  200 , and if the bi-pin  250  of this end happens to be first inserted into the live socket at one end of the fixture, then a shock hazard occurs because the shock protection switch  210  already allows the AC power to connect to the driver  400  electrically inside the LLT lamp when the bi-pin  250  is in the socket. Although the LLT lamp  600  is deactivated at the time, the LED driver  400  is live. Without the shock protection switch  310  at the other end of the LLT lamp  200 , the driver input  370  connects directly to the bi-pin  350  at the other end of the LLT lamp  200 . This presents a shock hazard. However, if the shock protection switch  310  is used as in accordance with this application, the current flow to the earth continues to be interrupted until the bi-pin  350  is inserted into the other socket, and the protection switch  310  is actuated. The switch redundancy eliminates the possibility of shock hazard for a person who installs an LLT lamp in the existing fluorescent tube fixture.