Patent Application
20150252958
The present invention relates to a retrofit LED lighting system, and more particularly to an edge-lit LED retrofit lighting system for a fluorescent tube.
A variety of LED retrofit light tubes exist in the prior art, these light tubes have the drawbacks of having a relatively narrow illumination angle and uneven light distribution. A diffuser is provided on top of the housing of the light tubes above the LEDs, the light emitted by the LEDs is diffused around the diffusion areas on the top. As a result, the illumination angle of the light tubes is still small, and a large part of the tube cannot emit light and forms a dark area.
Therefore, there is a need for a LED light tube that cost-effectively provides uniform illumination along the tube with an illumination angle of 180 degrees or above to cater to various illumination applications. There is also a need for a LED light tube that increases luminous efficiency and has a reduced loss of light energy.
An aspect of the present invention provides a LED retrofit tube that provides a replacement for a fluorescent tube. The retrofit tube is a LED tube that is based on edge-lit technology and is compatible with all known ballast types such as instant start, rapid start and programmed start ballast. The retrofit tube consists of a circuit that converts the AC waveform generated by the ballast into the DC waveform suitable for the LEDs.
The retrofit tube comprises a set of end caps that are placed at both the ends of the tube, each end cap has a PCB circuit at one side and has two pins on the other side for establishing electric connection with the socket; a set of hollow cylindrical heat sinks attached to each end cap for dissipating heat generated by the LEDs; a MCPCB plate mounted with a LED; a hollow or solid cylindrical light guide that guides the light generated from the LED mounted on the MCPCB plate to the other end. The emission angle in the retrofit tube is controlled by controlling the etching of the surface of the light guide. The PCB circuit is comprised of a bridge rectifier having schottky diodes, and a large capacitor that is placed in parallel to the bridge rectifier. The retrofit tube is compatible with the existing fluorescent ballast and hence does not require the removal of fluorescent ballast while replacing the fluorescent tube with the LED tube.
The preferred embodiments of the invention will hereinafter be described in conjunction with the appended drawings provided to illustrate and not to limit the scope of the invention, wherein like designation denote like element and in which:
In the following detailed description of the embodiments of the invention, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. However, it will be obvious to a person skilled in art that the embodiments of the invention may be practiced with or without these specific details. In other instances well known methods, procedures and components have not been described in detail so as not to unnecessarily obscure aspects of the embodiments of the invention.
Furthermore, it will be clear that the invention is not limited to these embodiments only. Numerous modifications, changes, variations, substitutions and equivalents will be apparent to those skilled in the art, without parting from the spirit and scope of the invention.
An LED retrofit tube that provides a replacement for a fluorescent tube driven by a ballast is further described herein. The characteristic of the LED retrofit tube over the conventional LED tube is that the retrofit tube of the present invention is based on the edge-lit technology. The LED mounted on the MCPCB plate is placed at the edge of the tube. The light emitted from the LED is passed through a light guide, a solid or hollow tubular structure that uses an internal reflection mechanism for guiding the light through the whole tube. The use of edge-lit technology enables the tube to be lit even by a single LED. The conventional LED tube based on direct lit technology must have a minimum LED count in the range of hundreds, so as to avoid pixilation on the lens. The light guide is made of optical grade materials such as acrylic resin, polycarbonate, epoxies and glass. In an aspect of the present invention, the light guide can be a U-shape or a circular, a cylindrical, a helical or a cubical structure.
In an aspect of the present invention the retrofit tube is designed to enable light output tuning to suit the user's requirement. The emission angle of the retrofit LED tube is controlled by controlling the etching of the light guide. The etching of the surface of the light guide enables the light to escape from the etched area. The surface can be etched so as to make the emission angle from as little at 90° or as much as 360° with different designs.
The circuit of the retrofit LED tube is comprised of a bridge rectifier that is used to convert the AC waveform of the fluorescent ballast to a single sided waveform, and a capacitor to filter the waveform to generate DC output to LED. The ballast can be an electronic ballast or an electromagnetic ballast.
The circuit may comprises a resistor placed in series with the input port, an inductor placed in series with the cathode input, a bridge rectifier that converts the AC waveform coming from the ballast to DC waveform, a capacitor placed in parallel to the bridge rectifier and the LED.
The front cover 102 is a circular tubular structure made of an elastic transparent material (such as a plastic material) that is an electrical insulator capable of avoiding electric shocks and a heat dissipating opening 108 is formed axially along the tubular housing 101. The plurality of LEDs is arranged on a panel that is mounted on the tubular housing 101. The pair of side covers 104 and 105 are made of an insulating material and respectively sheathed on both end portions of the transparent cover 101, wherein the side covers 104 and 105 contain the pair of electrical connection portions 106 and 107, and the electrical connection portions 106 and 107 are electrically coupled to the pair of side covers 104 and 105. In addition, each of the side covers 104 and 105 has a fixing hole formed at a position for installing and securing an insulating screw, and a nut portion of the insulating screw is made of an insulating material, so that after the side covers 104 and 105 are secured to both end portions of the front cover 101 or the side covers 104 and 105 are fixed directly to both end portions of the tubular housing 101 by an adhesive, a complete insulation effect can be achieved to prevent a possible electric shock that may occur when a user changes the fluorescent tube.
In an aspect of the present invention, the light guide can be a circular, cylindrical, helical or U-shaped.
In an embodiment of the invention, the LED 303 is mounted on a MCPCB plate 302 and is placed in between the first heat sink 202 and the light guide 201. The LED 303 is connected to the PCB circuit 301 placed in the inner housing on the first end cap 204. The one terminal PCB circuit 301 is electrically connected to the input pins on the first end cap 204 and the second terminal of PCB circuit 301 is connected to the input pins on the second end cap 205 through a wire that spans across the tube in the middle of the light guide 201. The MCPCB 302 is mounted perpendicular to the axis of the edge-lit LED retrofit fluorescent tube 200 such that the light emitted by the LED 303 strikes on the lateral walls of the light guide 201. The light guide 201 uses the phenomenon of internal reflection and the edge-lit technology propagates the light emitted by the LED 303 through the edge-lit LED retrofit fluorescent tube 200.
In an aspect of the present invention, the first heat sink 202 and the second heat sink 203 are present at both ends of the light guide 201, thus enabling maximum heat dissipation. The arrangement of the first heat sink 202, second heat sink 203 and the PCB circuit 301 not only prevents the PCB circuit 301 from subjecting to the high temperature due to the heat generated by the LED 303, but also ensures that the light emission of the LED 303 through the tube would not be hindered by the PCB circuit 301. The first heat sink 202 and the second heat sink 203 are configured to couple to the light guide 201 in a manner that the openings on the both end of the light guide 201 are completely covered resulting in a tubular structure. As illustrated in
The heat sink is preferably fabricated from a thermally conductive material selected from the group consisting of metals such as aluminum and aluminum alloy, plastics and ceramic. The material of the pair of heat sink preferably has a high mechanical strength, so that the tubular structure formed by coupling the pair of first heat sink 202, the second heat sink 203 and the light guide 201 together remains rigid in the required length.
In another aspect of the present invention, the edge-lit LED retrofit fluorescent tube may comprise a LED 303 mounted on the MCPCB plate 302. As the number of LEDs increase, the luminous intensity of the tube increases. However, in a preferred embodiment the number of LED mounted on MCPCB 302 is one.
In another aspect of the present invention, the light guide is etched to control the emission angle of the light. The etching is done to suit the lumen output requirement, for instance, if it is desired that the light emitted is to be spread at an angle of 180°, then the half of the light guide surface is etched, the light escapes from the etched surface of the light guide while un-etched surface restricts the light to escape from the tube. The surface of the light guide can be etched so as to allow the emission angle from as low as 90° to as high as 360°.
The MCPCB plate 302 has a LED mounting side on which the LED 303 is mounted and a heat transferring side opposite to the LED-mounting side for dissipating the generated heat through the first heat sink 202. The LED 303 on the MCPCB plate 302 is connected to the PCB circuit 301. The PCB circuit 301 is directly connected to the switch input connector 206 and 207 of the first end cap 204 and through a wire to the switch input connector of the second end cap 205. The wire spans across the light guide 201 passing in the centre of the light guide 201.
The LED light source can be a LED, a LED package or an LED array. The plurality of LEDs may be connected in series and/or in parallel, but they are mounted axially in a single straight line on the MCPCB plate 302. The arrangement of the LED 303 is particularly cost-effective in terms of the capacity of the heat sinks and the light output efficiency of the light tube. For example, the edge-lit LED retrofit fluorescent tube 200 is built with high-luminous efficacy LEDs and produces 2300 lumens at just 20 W, emit less heat (3.4 BTUs per hour versus 30 BTUs) and fit any T8 and T12 fixtures.
The light output of the edge-lit LED retrofit fluorescent tube 200 can obtain an enhanced luminous efficiency, and it has been found that the luminous flux of the edge-lit LED retrofit fluorescent tube 200 is increased with respect to the existing LED light tubes in the prior art for the reasons of improved light emission discussed below, hence low power LEDs can be used in the edge-lit LED retrofit fluorescent tube 200 to provide natural and evenly distributed light pattern. This saves energy and allows for a heat sink of smaller size.
The first end caps 204 and the second end cap 205 is designed to fit over the first heat sinks 202 and the second heat sink 203 respectively. In the embodiment, each end caps includes two pin connectors for connection to the fluorescent light tube socket. The two pin connectors are electrically connected to the socket for providing power to drive the LED 303. With such a wiring arrangement, the edge-lit LED retrofit fluorescent tube 200 can maintain its functionality no matter which direction it is plugged into the fluorescent light tube sockets. The end caps are made of plastic, or metal or a combination thereof.
Assembling the edge-lit LED retrofit fluorescent tube 200, involves electrically attaching the MCPCB 302, securing the MCPCB 302 onto the first heat sink 202 coupling both the ends of the light guide 201 to the first heat sink 202 and the second heat sink 203 and attaching the first end cap 204 to the first heat sink 202 and the second end cap 205 to the second heat sink 203 resulting in a tubular structure. The PCB circuit is connected to the switch input connector of the first end cap 204 directly and to the switch input connector on the second end cap 205 through a wire spanning across the tube through the centre of the light guide.
The thermal conductivity of the material of the heat sinks directly affects the dissipation of heat through conduction. The heat sinks can be made of aluminum or copper or thermoplastic material or a natural graphite solution that offers better thermal transfer than copper with a lower weight than aluminum. The heat sinks are made of natural graphite solution and they have the ability to be formed into complex two dimensional shapes.
In another aspect of the present invention, the edge-lit LED retrofit fluorescent tube can be used to replace existing fluorescent tubes such as T2, T3, T4, T5, T8, T10 or T12 fluorescent tubes. The edge-lit LED retrofit fluorescent tube is compatible with instant start, rapid start, and programmed start ballast. Thus, there is no need for removing the existing ballast structure and thus saves considerable cost by eliminating the need of a skilled person to remove the existing fluorescent tube and the ballast. The edge-lit LED retrofit fluorescent tube 200 has a PCB circuit 301 that comprises a bridge rectifier, and a large capacitor placed in parallel to the bridge rectifier. The bridge rectifier is made of schottky diodes that convert the high frequency alternating current generated by the fluorescent ballast to the direct current required for the working of LEDs.
