|Tuesday, 02 January 2007|
A lamp may be provided with power by a dimmer so that the lamp can be operated at variable, selected light intensity levels. In lighting systems, full brightness of the lamps used in the lighting system is not always needed or desired. For example, when sunlight is present in the area served by the lighting system, full brightness of the lamps may provide excessive lighting for the area or may exceed optimum lighting levels. It would be advantageous to have natural sunlight and artificial lighting from fluorescent lamps augment each other by dimming the artificial lighting to achieve a desired level of combined light intensity for the area. A dimmer permits lowered or raised light levels so that they are appropriate to the need. For example, luminaires for theatrical, architectural and other applications are often provided with operating power by dimmers. Luminaires for theatrical and architectural applications are provided with power by phase angle dimmers so that the lamps of the luminaires can be dimmed to operate at selected light levels. A fluorescent lamp is an electrical discharge device filled with a gas produced by vaporizing droplets of mercury within a closed tube. The inner surface of the lamp is coated with a fluorescent powder such as phosphor crystals. Electrodes are located at each end of the tube for trigger start and rapid start lamps. When a proper voltage is applied to the filaments, they heat and ionize the gas within the tube. The ionized gas in turn causes the fluorescent powder to emit visible light. The increased use of fluorescent lamps in residential service and increasing demand for light level control resulted in the development of household type fluorescent dimming devices, which control the light level but do not efficiently conserve energy. Resistive dimmers are variable resistor devices that reduce the power to the light bulb in accordance to the ratio between the resistances. The overall power consumed remains essentially unchanged. Pulse width modulation dimmers are used predominantly with fluorescent lighting. These dimmers have a better efficacy than standard dimmers, but such dimming devices are costly for both the replacement components and the installation. Capactive or inductive phase shifting dimmers incorporate capactive or inductive elements in the circuit to introduce a phase shift in the electrical supply to the light fixture.
Various dimmer systems have been developed for controlling power dissipation in a load. The simplest dimmer systems involve connection of a variable resistance in series or parallel with the load. These systems waste energy in the variable resistance. Conventional dimmer lighting systems have employed dimmer switch controls that include an on/off switch and an up/down power control, master unit and remote units, and microprocessor control for various power-up, power-down and fade in/out functions. Rather than use a variable resistor type rheostat which wastes power and generates heat at low illumination levels, modern dimming systems employ phase regulation, in which the power circuit is switched on at a time delay following a zero-crossing of the AC sine wave input until the end of each half cycle in order to supply a variable level of power to the lighting load. These dimmer switches typically employ solid-state devices such as triacs, silicon-controlled rectifiers, or field-effect transistors for varying the phase angle of an applied AC sinusoidal voltage. Most dimmers today are solid-state devices. Dimmer switches typically include mechanical components which provide only coarse adjustments to the illuminating device and other loads. When the dimmer switch regulates electrical power to an illuminating device in a vehicle dashboard, for example, the addition of other accessories in the vehicle can typically increase the load of the dimmer switch circuit to a level that can lead to damage to the dimmer switch and surrounding components. A wide variety of switch actuators are commercially available for controlling the switching of power between a power source and an electrical load. Many of these actuators either incorporate or are otherwise combined with a device for varying the level of power applied to the load, hereinafter referred to as a dimmer. The most common of these systems involves switching of the triac to the conductive state at some point on the waveform such that only a fraction of the complete waveform reaches the load. Triacs are commonly used to regulate the proportional electrical power delivered to a load, and comprise the main power control element of a number of conventional dimmer switches used to control electrical lighting control loads. A triac gate signal controls the portion of the time during each normal alternating current half cycle during which the triac is conductive in order to vary the power delivered to a load and therefore to control the intensity of a load such as an electrical lighting fixture. Dimmers may be operated with a toggle, a dial, a slide, a paddle switch, a touch-pad or electronic button; some types integrate two or more of these methods to handle different tasks. Dimmer switches are often provided in the form of modules or packs suitable for mounting in a rack along with other dimmers and, in some applications, with control modules.