Method and apparatus for illumination and communication

#The present invention pertains to the field of illumination and free-space optical communication, and more particularly, to the simultaneous use of a light source as an illumination device and a communication device.

#Light sources can be used simultaneously for both general illumination and for free-space optical communication if their luminous flux output can be varied such that a human observer does not perceive a disturbing or otherwise undesirable flicker. Typically the luminous flux is modulated at frequencies above the “critical fusion frequency” (IESNA Lighting Handbook, Ninth Edition. Illuminating Engineering Society of North America, New York, N.Y., 2000, p. 3-20). This frequency is generally accepted to be about 60 Hertz for illumination applications based on electric lighting, but may be as high as about 150 Hertz for direct-view applications such as video displays.

#A method and apparatus for free-space optical communications using visible light is disclosed by Dachs in U.S. Pat. No. 3,900,404. In particular, a 24 kHz oscillator that is amplitude-modulated with an audio signal drives the luminous flux output of a fluorescent lamp. A representation of such a drive signal is illustrated in FIG. 1. A similar apparatus disclosed by King et al. in U.S. Pat. No. 5,550,434 also incorporates amplitude modulation (AM) of an arc lamp with, for example, an audio signal.

#FIG. 1 illustrates a representation of an amplitude-modulated oscillating carrier signal according to the prior art.

#FIG. 2 illustrates a representation of a visible light LED communication system using a power-line modem according to the prior art.

#FIG. 3 illustrates the relative spectral power distribution of a phosphor-coated blue LED according to the prior art.

#The term “light-emitting element” is used to define any device that emits radiation in any region or combination of regions of the electromagnetic spectrum for example, the visible region, infrared and/or ultraviolet region, when activated by applying a potential difference across it or passing a current through it, for example. Therefore a light-emitting element can have monochromatic, quasi-monochromatic polychromatic or broadband spectral emission characteristics. Examples of light-emitting elements include semiconductor, organic, or polymer/polymeric light-emitting diodes, optically pumped phosphor coated light-emitting diodes, optically pumped nano-crystal light-emitting diodes or any other similar light-emitting devices as would be readily understood by a worker skilled in the art. Furthermore, the term light-emitting element is used to define the specific device that emits the radiation, for example a LED die, and can equally be used to define a combination of the specific device that emits the radiation together with a housing or package within which the specific device or devices are placed.

#As used herein, the term “about” refers to a +/−10% variation from the nominal value. It is to be understood that such a variation is always included in any given value provided herein, whether or not it is specifically referred to.

#The terms “light,” “lighting,” “illumination,” “radiation” and “color” are used interchangeably to define electromagnetic radiation of a particular frequency or range of frequencies in any region of the electromagnetic spectrum for example, the visible, infrared and ultraviolet regions, or any combination of regions of the electromagnetic spectrum.