This invention relates to the reduction of the stray electrical energy (SEE) from a high efficiency light bulb.
High efficiency light bulbs such as fluorescent bulbs, made to replace incandescent light bulbs, are becoming widely used because of their higher efficiency. They provide more light per watt of power consumed. These bulbs typically have the disadvantage of emitting more stray electrical energy (SEE) than incandescent bulbs.
The SEE is caused by high frequency electrical currents in the bulb. SEE may be electromagnetic radiation, electric fields, or combinations such as associated with the near field of an antenna. SEE may present a health risk depending on its intensity and frequency components.
Consequently, more attention needs to be paid to SEE from high efficiency light bulbs. A device for reducing high frequency components is disclosed in U.S. Pat. No. 6,424,125.
An apparatus and method for reducing the stray electrical energy (SEE) generated by a high efficiency light bulb, including its associated circuits, is described. A curtain of a conductive material is disposed about the bulb and electrically connected to the threaded base of the bulb. The curtain has openings through which light passes. The openings have a dimension, such as the radius of a circular opening, which is preferably at least a factor of three smaller than the distance from the curtain to the bulb's source of SEE.
A method and apparatus for reducing stray electrical energy (SEE) from a high efficiency light bulb is described. In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. It will be apparent to one skilled in the art that the apparatus and method of the present invention may be practiced without these specific details. In other instances well-known fabrication techniques are not described in detail, in order not to unnecessarily obscure the following description.
Referring to
Referring to
In the electronic bulb circuits, the SEE is caused, in part, by switching transients and the like. The SEE radiates typically from the entire bulb, including the section 30 shown in
In accordance with the present invention, a shield is disposed about the bulb including sections 30 but not the base or contact 26). The shield comprises a curtain 36 forming the upper part of the shield which extends from the top of the bulb to its base, and a connection, shown as connection 37, which connects the shield to the base 28. The curtain 36 is electrically conductive with the connection 37 provides an electrically conductive path between the curtain 36 and the threaded base 28. The curtain is generally cylindrically shaped, to fit over the bulb. It is preferably fabricated from a wire mesh having a plurality of openings. These openings allow light to pass from the bulb into the surrounding regions. The size of the openings and their relationship to the bulb are discussed later in conjunction with
For reasons that will be explained, in some embodiments, the curtain 36 is encased or enclosed within an insulator. In
In a typical electrical power distribution arrangement, such as used in virtually all U.S. homes and businesses, the threaded base 28 of the bulb engages the “white” power lead which is at zero potential or ground potential. Consequently, the connection 37 connects the curtain to ground. It is this connection which causes the SEE passing through the curtain to be substantially attenuated. (The amount of this attenuation is discussed later.) In more modern wiring systems a 110, 3-prong plug is used with a centrally disposed round prong providing a ground connection. This type of plug can only be inserted one way into a power receptacle. For this reason, if the power wiring is correct, one prong of the plug is always at ground potential. This prong will be connected to the base 28.
In some cases, the power wiring may not be correct, or an older two-prong plug may be used installable in two possible ways into the power receptacle. Then, it is possible that the base 28 is at a high potential, relative to ground. When this occurs the curtain will be at a high potential and can cause an electrical shock. That is why, for some embodiments, an insulator 40 is used around the curtain (See
In using the shield of the present invention, a power plug may first be tested to determine if it is wired properly. Also the shield itself may be checked to determine if it is at ground potential. Numerous commercially available testers may be used to confirm the ground connection such as the “Voltalert” from Fluke®.
In the embodiment of
In
In
In the embodiment of
In the book Electromagnetic Compatibility Handbook by Kenneth L. Kaiser, published by CRC Press (copyright 2005) (Kaiser book), beginning at section 24.21, there is a discussion concerning the gain of a circular aperture when uniformly illuminated by a plane wave. Other sections of the Kaiser book describe coupling through an aperture, and the electric field along the axis of a circular aperture versus distance relative to the aperture's radius. This is helpful in understanding the attenuation of SEE provided by the shields described above. In general, the equations used in the Kaiser book describe the attenuation for a circular opening. The curtain of the shield may not have circular openings, but rather square, hexagonal, octagonal, or other shaped openings. For purposes of using the equations in this book, an approximation can be made for other openings by selecting a dimension of the opening, corresponding to the radius of a circle. For instance, for a square mesh such as shown in
The electric field along the axis of the opening attenuates logarithmically with the distance from the field's source. This is shown in FIG. 24.20 in the Kaiser book. Where “a” is equal to the distance from the field's source, the attenuation is approximately 1/10th. Ideally the dimension of the opening (A) should be smaller than the distance from the SEE source, preferably by three or more. For a factor of three the attenuation is 1/100th.
The distance from the source to the curtain is shown as “b” (in
Thus, a shield for reducing SEE from a high efficiency light bulb has been described.
Number | Name | Date | Kind |
---|---|---|---|
3885150 | Ott | May 1975 | A |
5731663 | Davis | Mar 1998 | A |
6424125 | Graham | Jul 2002 | B1 |
20020172037 | Schnaufer et al. | Nov 2002 | A1 |
20050117340 | Lee et al. | Jun 2005 | A1 |