Fluorescent light ballast with information transmission circuitry
First Claim
1. An electronic ballast for gas discharge lighting which is energized with a periodic waveform, said electronic ballast being coupled to a plurality of gas discharge lamps that provide a gas discharge light output, means for operating upon said gas discharge light output such that at least a portion of said light output from said gas discharge lamps is substantially proportional to an absolute value of an instantaneous waveform of lamp current, photo-detection means for detecting said at least a portion of said light output at a remote distance from said electronic ballast, said ballast containing modulation means for modulating said light output, said ballast containing at least one input port for entry of input signals from an external source into said modulation means, and means for introducing information to said input port so that the discharge light output of the gas discharge lamps can carry the introduced information.
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Accused Products
Abstract
The present invention features an electronic fluorescent lighting ballast which provides a way to transmit data by modulating the light that is emitted from lamps in a luminaire. The modulation occurs at a sufficiently high frequency, so that it is imperceptible in the range of human vision. Data can be represented in the emitted light by frequency-, phase- or amplitude-modulation. Communication methods can be either simplex or duplex. In the preferred embodiment, a simple modification of the base circuit of a typical, Class D, bipolar, push-pull inverter permits frequency- or phase-modulation of the inverter waveform. This causes modulation of the emitted light from the lamps of the luminaire. The transmission of data through an otherwise conventional lighting luminaire is desirable for many commercial applications. One example of its usage is in the transmission of audio or digital information in a grocery or department store from a centralized computer to display units on store shelves. Another example of its usage is in the transmission of audio or digital information from a central computer to various fixed or portable display terminals in an airport, providing arrival and departure information.
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Citations
30 Claims
- 1. An electronic ballast for gas discharge lighting which is energized with a periodic waveform, said electronic ballast being coupled to a plurality of gas discharge lamps that provide a gas discharge light output, means for operating upon said gas discharge light output such that at least a portion of said light output from said gas discharge lamps is substantially proportional to an absolute value of an instantaneous waveform of lamp current, photo-detection means for detecting said at least a portion of said light output at a remote distance from said electronic ballast, said ballast containing modulation means for modulating said light output, said ballast containing at least one input port for entry of input signals from an external source into said modulation means, and means for introducing information to said input port so that the discharge light output of the gas discharge lamps can carry the introduced information.
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29. An electronic ballast for gas discharge lighting which is energized with a periodic waveform, said electronic ballast being coupled to a plurality of gas discharge lamps that provides a gas discharge light output, means for operating upon said gas discharge light output so that at least a portion of said light output from said gas discharge lamps is substantially proportional to an absolute value of an instantaneous waveform of lamp current, photo-detection means for detecting said at least a portion of said light output at a remote distance from said electronic ballast, said ballast containing modulation means for modulating said light output, said modulation means comprising an inverter and a network for generating said light output, said inverter further comprising a base drive circuit that is coupled and phased to said network in order to provide a positive feedback, said ballast containing at least one input port for entry of input signals from an external source into said modulation means, and means for introducing information to said input port so that the discharge light output of the gas discharge lamps can carry the introduced information.
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30. An electronic ballast for gas discharge lighting which is energized with a periodic waveform, said electronic ballast being coupled to a plurality of gas discharge lamps that provides a gas discharge light output, means for operating upon said gas discharge light output so that at least a portion of said light output from said gas discharge lamps is substantially proportional to an absolute value of an instantaneous waveform of lamp current, photo-detection means for detecting said at least a portion of said light output at a remote distance from said electronic ballast, said ballast containing modulation means for modulating said light output, said modulation means further comprising a self-oscillating, bipolar inverter that is coupled to said plurality of gas discharge lamps, a base current of said ballast being modulated between discrete binary levels so as to encode data in an oscillation of said self-oscillating, bipolar inverter in a frequency-shift-keyed mode of frequency modulation, said ballast containing at least one input port for entry of input signals from an external source into said modulation means, whereby information introduced to said input port is carried upon the discharge light output of the gas discharge lamps.
Specification