Illumination – Light source and modifier – Laser type
Reexamination Certificate
2000-04-11
2002-05-28
Cariaso, Alan (Department: 2875)
Illumination
Light source and modifier
Laser type
C362S229000, C362S231000, C362S259000, C362S800000
Reexamination Certificate
active
06394626
ABSTRACT:
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 12-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 VAC). 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 5 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.
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Cariaso Alan
LumiLeds Lighting U.S., LLC
Skjerven Morrill & MacPherson LLP
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