This invention relates to a starting circuit for an electrical discharge lamp, and more specifically to a starting circuit that pre-heats the electrical discharge lamp above a predetermined temperature before illumination.
An electrical discharge lamp such as a fluorescent lamp, neon sign, mercury vapor light, and sodium vapor light, includes a pair of electrodes and an amount of mercury and inert gas(es) sealed inside a glass tube at a low pressure. The inside of the glass tube may be coated with a phosphor that produces visible light when excited by ultra-violet radiation. The pair of electrodes may be filaments that can be heated during a starting process to preheat the gases inside the glass tube in order to decrease the voltage requirements. When the lamp is off, the gases inside the glass tube are non-conductive, so when power is first applied, a high voltage is needed to initiate the discharge. These high voltages exhaust the filaments and therefore decrease the life of the lamp. However, once the initial discharge occurs, much lower voltage, usually under 100 V for tubes under 30 watts, and 100 to 175 V for 30 watts or higher, is needed to maintain the discharge. The electric current flowing through the gas filled glass tube emits ultra-violet radiation, and the internal phosphor coating converts the ultra-violet radiation into visible light. One can modify the mix of phosphor used inside the glass tube to control the light spectrum that is emitted for a specific application.
In one application, a mercury vapor electric discharge lamp may be used in the production of ozone, O3, in a means to purify water. Ozone is produced when oxygen, O2, is exposed to an electrostatic discharge, or when oxygen contains gas absorbed ultra-violet radiation. Common ozone generators for water purification involve using an electric discharge lamp that emits ultra-violet light that converts oxygen to ozone. Ozone generators may be configured for use in a spa or hot tub in order to purify or cleanse the water. In such capacity, the ozone produced would be injected into the water where bacteria, viruses, and organic and inorganic compounds would be destroyed.
Electric discharge lamps including mercury vapor electric discharge lamps are started in a variety of ways. One such way is using a glow tube starter that includes a switch which is normally open. Once power is applied to the glow tube starter, a glow discharge takes place which heats a bimetal contact. A small amount of time later (about 1 second) the contacts close which provides a current to the filaments, and since the glow is extinguished, the bimetal is no longer heated and the contacts open. An inductive kick generated at the instant the contacts open, triggers the main discharge in the lamp. However, if the contacts open at a time when the current is near zero, then there will not be a large enough inductive kick to start to the lamp. Therefore, these starters may be unreliable.
Another example of a starter is a pulse starter that is pin compatible and contains electronic circuits that detect the proper time to interrupt the filament circuit to generate the optimal inductive kick to trigger the main discharge. Similar to the glow tube starter, an inductive kick is needed to trigger the main discharge which lowers the life of the lamp by exhausting the filaments. Therefore, what is needed is a starter that provides reliable starting and prolongs the life of the lamp.
The devices and methods of the present invention address these and other needs.