Low interference lighting system

Details Low interference lighting system Low interference lighting system

2000-01-07

2001-08-21

Vu, David (Department: 2821)

Electric lamp and discharge devices: systems

With electromagnetic wave radiation preventing or shielding...

C315S127000

Reexamination Certificate

active

06278240

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to lighting systems, particularly ones that emit a minimum amount of interference signals.
BACKGROUND OF THE INVENTION
Lighting systems having a power source, structural and power connections to one or more light sources are widely used in industrial, commercial and domestic environments. Since these electrical systems may be extended and carry substantial amount of alternating current, substantial amount of electromagnetic (“EM”) radiation may be generated. The EM radiation may interfere with the operation of co-existing electrical or electronic appliances. Therefore, regulatory authorities in various countries have mandated the maximum amount of EM radiation an electrical appliance may emit in a specified environment.
With the advent of the high efficiency light sources such as those using low voltage halogen lamps, the problem of EM interference becomes more acute. Many of these light sources operate with a much lower operating voltage than line voltage. A voltage converter or transformer is required to change the line voltage to the lower operating voltage. The conversion process often results in the generation of EM interference signals. This is particularly true for low-cost electronic voltage converters operating under the principle of power switching. The switching rate is typically in the radio frequency portion of the EM spectrum. Also, the lower operating voltage requires a higher operating current to maintain a given power output. The higher operating current also results in a higher emission of EM interference signals.
FIG. 1
illustrates schematically a top view of a conventional lighting system
10
. The lighting system
10
is typically hung from a ceiling or mounted on a stand. It has a number of low voltage lamps
20
attached to and commuting with a pair of rails
30
. The pair of rails are usually fashioned out of chrome plated copper or steel rods extending from a housing
40
and may terminate with a non-conducting, decorative end bar
32
. The housing
40
houses a power supply which is typically a transformer or a voltage converter
50
. The voltage converter
50
converts a line voltage such as 110 or 220 V AC at 50 or 60 Hz to a substantially lower voltage, e.g., 12 VAC, at a substantially higher frequency, e.g., 20 kHz. The voltage converter
50
outputs this lower voltage at higher frequency to electrify the pair of rails
30
. The lamps
20
each has a pair of leads
22
that makes electrical contact with the pair of rails.
FIG. 2
shows a partial, perspective side view of the conventional lighting system
10
of FIG.
1
. Since the rails
30
of the lighting system
10
carry high frequency and high current electrical power, they act as antennae emitting radio frequency EM emissions. These high frequency emissions interfere with the operations of surrounding electronics such as televisions, telephones, radios and computers.
OBJECTS AND SUMMARY OF THE INVENTION
It is a general object of the present invention to provide a lighting system with low interference.
It is an object of the present invention to provide an efficient, low-cost and low interference lighting system having electrified rails for supplying power to a plurality of electrical appliances such as light sources.
These and other objects of the present invention are accomplished by the lighting system including a housing, a voltage converter located within the housing, at least one pair of spaced-apart arms attached to the housing, and one or more electrical appliances such as light sources each mounted on a section of the pair of arms and making electrical contact with the arms by a pair of contact conductors. With respect to each arm, it includes an elongated conductor and a grounded conducting shield surrounding, but electrically isolated from, the elongated conductor. One contact of the pair of the contact conductors makes electrical contact with the elongated conductor and not the grounded conducting shield.
When the housing is connected to a power source, the voltage converter converts the line voltage of the power source to a substantially lower voltage at a substantially higher frequency and thereby outputs it to the elongated conductors of at least one pair of spaced-apart arms. Since the elongated conductors are shielded by the grounded conducting shield, they emit negligible interference signals while they provide power to the electrical appliances via the contact conductors.


REFERENCES:
patent: 5030889 (1991-07-01), El-hamamsy et al.

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