Fluorescent lamps require relatively high starting voltages, and in many cases electrode heating. These are supplied by a combination of transformer coils, capacitors and solid state electronics, all usually potted together in a metallic enclosure commonly known as a “ballast”. The modern electronic ballasts have much smaller, lighter coils and relatively much more extensive electronic circuitry. These electronic ballasts may be potted, or their components may be coated only lightly, or have no coating at all.
A typical indoor fluorescent-lamp fixture or luminaire is an elongated, narrow structure with an even narrower, shallow casing that extends the length of the fixture for mounting of fluorescent-lamp sockets and for housing of the ballast and the fixture wiring. The ballast usually fits within or upon, one of these narrow, shallow casings and is thus usually made relatively long, narrow and shallow. The ballast has its own enclosure, usually made of two sheet-metal pieces. One piece is die-cut and then bent to provide two generally vertical side walls, a generally horizontal floor, and conventionally a vertical wall at each end of the enclosure respectively. A second, flat piece (with mounting holes for attachment to the casing) forms a separate cover plate.
General practice in the fluorescent-lighting industry for more than a half century has been to provide wires that extend from within the ballast through a grommet or strain relief in each end wall, respectively. Some of these wires connect with a lamp socket mounted at each end of the lamp fixture, respectively; and others of the wires connect with the input power leads.
The ballast wires sometimes are made the correct length to just reach the sockets in some particular lamp model, and sometimes are made shorter, for attachment to other wires—often called the “wiring harness” which then extends the remaining distance to the sockets. Representative patents exemplifying this standard configuration include U.S. Pat. No. 2,489,245 to Sola, U.S. Pat. No. 2,595,487 to Runge, U.S. Pat. No. 3,360,687 to Riesland, and U.S. Pat. No. 3,655,906 to Robb.
Adherence to this basic form of ballast wiring has remained dominant in the industry despite issuance of many patents proposing seemingly reasonable variations. U.S. Pat. No. 2,487,468 issued in 1949 to Shirley R. Naysmith for one such variation in which the wires from each end of the ballast terminate in respective half-connectors that plug directly into mating half-connectors in lamp-socket assemblies, at the ends of the fixture.
The Naysmith patent discloses wiring within the luminaire that is completed by plugging together the cable-carried receptacles to the fixed lamp holders” so that fixture assembly would be rendered so easy that ballast units may be completed and pretested by the ballast manufacturer, the lamp holders by the lamp holder manufacturer, and shipped to the installation location in suitable lots without passing through the factory of the fixture manufacturer. Naysmith's device is not a “leadless” ballast.
U.S. Pat. No. 3,514,590 issued to Shaeffer discloses a leadless ballast that plugs into a printed-circuit board that replace both the casing and the wiring of a fluorescent-lamp fixture with the lamp sockets and the plug-in ballast supported at the underside of the printed-circuit board. Shaeffer's objective was that the entire fixture be amenable to assembly quickly and without the use of tools.
U.S. Pat. No. 3,569,694 issued Comer describes a ballast-can cover plate that is extended longitudinally beyond one end wall of the can, and an array of laterally oriented connector pins fitted to a vertical bracket on the base plate extension. Short wires are passed to these pins through the end of the ballast can and the pins are mated with mating contacts mounted to the casing of the fixture. This unit is almost leadless.
The plug-in concept was carried an extreme in U.S. Pat. No. 4,674,015 issued to Smith, which teaches that the entire ballast should be plugged bodily sideways into a large receptacle in the casing. In Smith's leadless design, contact tabs on the interior wall of the receptacle engage mating contact tabs on the side wall of the ballast can.
U.S. Pat. No. 4,729,740 issued to Crowe shows a small printed-circuit board within the ballast can and supporting all the other components in the can. In particular the internal circuit board a respective electrical connector at each end for attachment of several individual leads of a wiring harness leading to each end of the fixture. Crowe's ballast is also a leadless configuration.
The ballast disclosed in U.S. Pat. No. 4,277,728 has a full-length circuit board generally analogous to Crowe's but mounted to a flat plate that becomes the cover, rather than to the U-shaped body. It also has a second board that is much shorter and mounted vertically to the full-length board. The ballast is not potted, although some of the components are individually dipped and the ballast has various other features including a connection for computerized control, and a manual dimmer control.
Another leadless ballast design that uses an internal connector is disclosed by Burton et al. in U.S. Pat. No. 4,916,363 has an internal connector that receives the wiring-harness wires either individually or in a connector-like carrier that organizes the wires into an array, but the internal connector is not mounted in the picture-frame style as in Crowe. Instead the internal connector is mounted in a transverse slot that extends all the way across the width of the bottom of the can, about a quarter or a third of the distance along the can from one end. At the side of the internal connector which faces toward that nearer end, the bottom of the can is formed in a shallow bevel that makes the connector face accessible for insertion of the wires.
U.S. Patent No. 5,350,316 discloses fluorescent-lamp leadless ballast with an improved connector. The half-connector body has lateral ears that fit in small notches in the ends of the side walls of a ballast can. An end wall traps the ears longitudinally in the notches to enhance tight longitudinal fit. Outside the ballast, in a new fixture, a jack slides freely in the receptacle to make wiring-harness connections. In either the jack or receptacle, cylindrical female contacts mate with bared ends of standard fixture wires held in the opposite half connector, serving as pin contacts. When the female contacts are in the jack, a person may replace conventional ballasts with this new one, by cutting and baring the old harness wires and inserting them individually into the receptacle. Alternatively, for field retrofit a jack can be supplied, e.g. with poke-in wiring.
The prior art addresses various methods of adapting a connector to the ballast for the purposes of quickly changing the wiring, yet the mechanical process of replacing the ballast is still a slower task, as the physical location of the ballast is still within the inner space of the lamp fixture. Nor does the prior art address the issue of waste heat generated by the ballast, which the new invention addresses by locating the ballast in the plenum space above the lamp fixture, and thermally isolating the ballast from the fixture while still remaining electrically grounded to the chassis.
In the existing architecture of a fluorescent lighting fixture, the lamp ballast is physically, electrically, and thermally attached to the interior of the light fixture. No wire harness is used, requiring semi-permanent methods of lamp and power wire. Typically wire connections are done with plastic wire nuts for input power and ballast leads are directly connected to lamp holders. To gain access to the lamp ballast for the installation and removal of the lamp ballast it requires the removal of the lamp fixture lens or outer louver, usually at least one light tube and ballast covering plate. Many sites and local codes require specialists for the repair. The physical replacement process is cumbersome and time consuming. The replacement further impacts the owner with relatively expensive repair costs and reduced productivity.
The lamp ballast is located on the human occupied, or air-conditioned, side of the light fixture and not on the side that is exposed to the plenum space. This combined with the fact that the ballast is thermally connected to the light fixture, causes most of the heat generated by the ballast to be directed to the conditioned space. HVAC designers account for this heat by increasing air conditioning capacity.
What is needed is a lamp ballast as either a retrofit to existing lamp fixtures or as a change to newly manufactured lamp fixtures that is easily installed and replaced while reducing the amount of generated heat that is transferred into the living space.