A FLEXIBLE LIGHT TRACK FOR SIGNAGE

Abstract: The invention is an outdoor lighting display using light emitting devices. A flexible light track is secured at the bottom of a channel, e.g. a letter or symbol. A top corresponding to the shape of the channel covers the channel to protect the flexible light track from weather changes. The flexible light track includes a plurality of plastic modules having electrical connectors and respective tracks. Light emitting devices (LEDs) are inserted in the plastic modules. Electrical wires are positioned in the tracks of the plastic modules such that the LEDs are electrically connected in parallel.

Description: A FLEXIBLE LIGHT TRACK FOR SIGNAGE Field of the Invention The invention is directed towards the field of illuminated signage particularly towards using light emitting diodes in channel letters or band lights. BACKGROUND Prior art in the sign industry is mostly neon, florescent and incandescent lighting. Neon has been the predominant illumination source for commercial signage. It is used by many vendors and is available globally. Neon has well known problems. Neon is hard to bend to fit i2-inch or smaller channel letters. Neon has difficulty starting in cold weather, e.g. Minnesota in winter. The associated mean time to failure depends upon the operating environment, often 3 to 5 years of use. The operating voltage of 1000 volts that follows a turn-on voltage of many thousands of electrical volts, e.g. 10,000 volts is a recognized public safety hazard. Furthermore, disposal of the mercury used in some neon signs is an recognized environmental hazard. Florescent lighting is used in many larger commercial signs. It is very inexpensive technology with well-known properties. While there are some shaped florescent lamps, most are straight tubes having a length between two and eight feet. This limits their use to very large signs. Similar to neon, florescent lamps are difficult to start at cold temperature and a short mean time to failure. The lamps are powered using AC voltages (120 or 220 NAC). This is still considered a high voltage level and therefore public safety hazard. Florescent lights are typically available in white that limits their applications in signage. Incandescent lighting is. comparably inexpensive next to neon and florescent lighting. Unlike the other lighting mentioned, they have no problem with cold weather. However, they have a relatively short mean time to failure because they produce a lot of heat and are fragile. They are the least power efficient option for commercial signage and the power cost is often significant. They can be operated at voltage levels safe to the public. Furthermore, the color shifts continuously during their life. Light emitting devices (LEDs) are more power efficient than incandescent and neon- LEDs are inherently long life devices, essentially life long devices for commercial signs. They are inherently single color light sources. As single color illuminators, they are more efficient then the other technologies mentioned for colored light. They are inherently rugged devices that do not need special handling for shipping or installation. Their quality is not dependent on skilled craftsmen. They are inherently low voltage, safe devices, often operating below s volts. In the prior art, the LEDs are mounted on printed circuit boards that are expensive and difficult to customize because they are inflexible. The LED light output is temperature dependent and degrades with use. SUMMARY The invention is an outdoor lighting display using light emitting devices. A flexible light track is secured at the bottom of a channel, e.g. a letter or symbol. A top corresponding to the shape of the channel covers the channel. The top is made of a translucent material, usually acrylic. The flexible light track includes a plurality of plastic modules having positive and negative electrical connectors and respective tracks. Light emitting devices (LEDs) are inserted in the plastic modules. The LEDs are more energy efficient than neon displays and are easier and less expensive to replace. Electrical wires are positioned in the tracks of the plastic modules such that the LEDs are electrically connected in parallel. As the LED light output varies most directly with current, but the voltage across the LED varies with material type, temperature and manufacturing variations, the LEDs in a string are matched. There is less variation in light output when driven from a constant current source. The first LED of a string can be fed back to the system controller to allow the voltage to be set to maintain constant current in all modules of the string over temperature, and material type. White light can be created by using two or three colored LED rails, usually a red, green, and blue (RGB) combination. Other colors can also be created by mixing light from two or more colored LED modules. The system controller may be open loop. When good color control, or color temperature control is needed, photo feedback is built into the controller. Precise control by open loop techniques is difficult because the light output from the LEDs varies with changes in temperature and degrades at differing rates for different material technologies. The photo diodes can be built into the controller, built into the LEDs, or mounted separately in the channel letter. The colored LEDs may be placed in discrete modules or integrated into a single module. There are several techniques that can be used for color separation. The drawings show a photodiode in the LED package. The color separation occurs because each package contains only one light. An alternate color separation can use a single photodiode that sits within the channel letter where it is exposed to light reflected back from the transparent top and the color separation done by momentarily testing measuring each color sequentially. Since the balance between colors degrades slowly with age or temperature, the measurement could be made infrequently. The color separation can also be done with photodiodes that have color filters over the photo diodes. The color filter often chosen would be the X and Y filters described by the CIE organization. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 shows a lighting system of the present invention. Figures 2A-C illustrate embodiments of the housing shown in Figure 1. Figures 3 A-C illustrate mounting techniques. Figures 3 A-B illustrate embodiments for the bendable clip assembly. Figure 3C shows the snap clip. Figure 4 shows the LED rail attached to the bottom of a channel letter. Figures 5A-B illustrate multiple color LED rail embodiments. DETAILED DESCRIPTION OF THE DRAWINGS The invention is a flexible light track lit by a distributed power system. High voltage AC mains can be kept behind a wall and handled without extraordinary care. The system can be used in locations requiring channel letters or light bands that are white, dynamic, or custom shades. A flexible light track is preferably secured at the bottom of a channel-shaped housing, e.g. a channel light or light band. The LED rail can be fastened via bendable clip, adhesive, or a snap in plastic clip. A colored translucent top covers the housing to provide reflected sun light color during the daytime. The LEDs provide the illumination from underneath at night. The flexible light track includes a plurality of plastic modules with LEDs. The LEDs are more energy efficient than neon displays and are easier to assemble. They are inherently reliable and do not require servicing. A system controller powers the LED modules. The system controller can be a simple current source or current sink but can include additional features such as intensity control, dynamic changing colors or light levels, or to maintains color point in white light applications. The controller may compensate for LEDs over temperature and life of the LEDs using a photodiode signal. Electrical wires are positioned in the tracks of the plastic modules such that the LEDs are electrically connected in parallel strings. Figure 1 shows a schematic diagram of the present invention. The LED rail 10 is powered by an external supply 12, e.g. 24 VDC, with individual LED modules in strings powered by a LED controller 14. As the light output from an LED degrades slowly with time, an optional version of the system controller 14 can be used to power the LED rail 10 via an optional reference module 16 to provide accurate color and intensity control. The flexible LED rail 10 includes a plurality of modules 18x. The modules 18x are fastened to the channel letter and are electrically connected in parallel via two wires 20A, 20B. Figures 2A-C illustrate embodiments of module 18x shown in Figure 1. The module 18x has electrical contacts 22 A, 22B that form insulation displacement connectors for the two wires 20A, 20B from the LED rail and a lamp 24, e.g. LED. Each electrical contact 22A, 22B spans a corresponding track. The LED modules include a snap feature to allow a secondary optic (not shown) to be fastened over the LED. The secondary optic is used to change the radiation pattern to optimize for different depths, change apparent source size, or to create artistic patterns such as the crystal look. The lamp 24, e.g. a high power LED, is pressed , or soldered into complete a module. A bendable clip assembly 26 retains the module and pre-loads against the lamp to create intimate thermal contact. Optionally, heat transfer goo or adhesive may be positioned between the bendable clip assembly 26 and the lamp 24 to promote heat transfer. In Figure 2C, the LED 24 is integrated into the module. The LEDs are held in place by a bendable clip assembly that includes a metal frame (bendable clip) and a mounting adhesive. The bendable clip mechanically holds the LED modules. The clip serves as a template for positioning the modules along the bottom of a channel, attaches the modules to the bottom of a channel, and serves as a heat sink for the LEDs. The bendable clip metal frame is formed sheet metal. The formed side walls have various slot cuts which allow the bendable clip to turn at large angles relative to the plane of the side walls, which allows the bendable clip to bend with a small tight radius around sharp corners or radii in channels. The bendable clip in Figures 3 A-B mechanically holds the LED modules. The sidewalls of the bendable clip are the clips. The clips are bent or preloaded, so that when a module is inserted between the clips, compressive forces are applied onto the module to hold it in place. The module is inserted into the bendable clip from the top; during the insertion, the walls flex, elastically, outward and clamp onto the module. The bendable clip can serve as a template for positioning the modules along the bottom of a channel shown in Figure 4. The bendable clip attaches the modules to the bottom of a channel. The bendable clip can be mounted to the bottom of a channel by tape adhesive, a spray adhesive, or rivet pins. The bendable clip is made from metal. The bendable clip conducts the heat out through the adhesive tape to the channel, and the channel then conducts (by conduction, convection, or radiation) the heat to its surroundings. The bendable clip also conducts some of the heat directly into the air or surrounding as depicted by the heat path through the sidewalls. Figures 5A-B illustrate schematic diagrams for the multiple color LED rails. In Figure 5 A, the power supply/system controller 12, 14 connected to three discrete LED rails. In Figure 5B, the three LED rails are integrated into the same module. Two or three color LED rails can be controlled in combination to create white light and other colors. The LEDs within a string are matched with the first module having an integrated photodiode to feedback light level. The system controller measures the light level from a reference LED matched to the string and sets current/voltage to maintain the desired color mix.

Claims: CLAIMS We claim: 1. A flexible assembly comprising: N modules, where N = 1 , each module including, a housing having a positive and a negative track, and a positive and a negative connectors, the positive connector straddling the positive track, the negative connector straddling the negative track; two wires, one being electrically connected to each, positive connector, the other being electrically connected to each negative connector; and a LED system controller to power the plurality of modules. 2. A flexible assembly, as defined in claim 1, each module further comprising a light emitting device being electrically connected to the positive and negative connectors. 3. A flexible assembly, as defined in claim 2, wherein the light emitting device is a high power light emitting diode. 4. A flexible assembly, as defined in claim 2, further comprising: a housing having three sides and an open side; and a translucent cover, positioned on the open side; wherein the two wires are positioned along one of three sides. 5. A flexible assembly, as defined in claim 4, further comprising a plurality of clips positioned along one of three sides, wherein the clips secure the two wires.

Inventors: MCCOLLOCH LARRY, MCCOLLOCH, LARRY
Applicants: LUMILEDS LIGHTING LLC, LUMILEDS LIGHTING, U.S., LLC
Application year: 2001
Main classification: F21V
IPC codes: F21S2, F21S4, G09F9, G09F13, H01L33