Generally, fluorescent lamps operate from a 50 to 60 hertz alternating current source and emit radiation in the visible region of the spectrum. This visible radiation is provided by an internal phosphor coating or a light transmittable glass envelope which is excited by ultraviolet radiation produced in a low pressure mercury-rare gas vapor discharge operating within the glass envelope. Normally, this vapor discharge has a negative volt-amphere characteristic and the current of such a plasma will tend to continuously increase in magnitude if not restrained by a current limiter or ballast in series connection therewith.
Conventionally, the electrical circuit of a fluorescent lamp system includes a starter, an inductor ballast or combination inductor ballast and step-up transformer and a fluorescent lamp. The ballast and fluorescent lamp are series connected such that the sum of the instantaneous voltage drops across the ballast and the lamp is equal to the applied service voltage. Unfortunately, the three instantaneous voltages may not necessarily be in phase and, as a result, the root means square (RMS) values of the lamp voltage and the ballast voltage may not equal the service voltage. Moreover, experience indicates that the RMS value of the voltage across the typical fluorescent lamp utilizing only an inductive ballast is about one-half or 50% of the rated RMS value of the applied service voltage. Thus, the size or voltage rating of a lamp suitable to ordinary circuitry is seriously limited by the service voltage value and the restrictive one-half or 50% thereof available across the lamp. In other words, lower voltage lamps are usually necessitated because of availability thereacross of only about 50% of the service voltage when applied to the lamp and an inductor ballast combination.
Additionally, it has been found that an increase in potential applied to a fluorescent lamp is particularly effective in increasing light output therefrom. More specifically, potential applied to a fluorescent lamp can be separated into three distinct voltages, i.e. cathode fall voltage, positive column or arc drop votlage and anode fall voltage. Since the cathode and anode fall voltages remain substantially constant for any given lamp geometry, it follows that an increase in voltage applied to the lamp is primarily added to the positive column or arc drop voltage. Moreover, it is this positive column or arc drop voltage which controls the ultraviolet radiation and, in turn, excitation of the lamp phosphors and production of light. Thus, increased voltage available to the fluorescent lamp has a very significant effect upon the percentage increase in light available from the lamp.
One known technique frequently employed to increase the potential available to a discharge lamp is to utilize a step-up transformer and a fixed capacitor. In this manner, an increased potential appearing at the capacitor is available to the series connected inductive ballast and discharge lamp. However, transformers are expensive and cumbersome adding greatly to the apparatus cost while a fixed capacitor must be of increased size in order to provide a voltage of increased magnitude. Moreover, larger size capacitors add to the apparatus cost.
Another known apparatus for improving the operation of a ballast and discharge lamp is suggested in U.S. Pat. No. 3,996,495 issued to Herman on Dec. 7, 1976 and bearing the title "High Efficiency Ballast System For Electric Discharge Lamps". Therein, a non-linear capacitor is connected in series with a conventional high resistance transformer and allegedly improves the lamp current crest factor. Thus, lamp efficiency is reportedly improved because of an improved lamp current crest factor. In this manner, lamp current can be reduced without loss of liquid output. However, starting and maintaining ignition of increased wattage lamps remains a problem.
Another known apparatus suggesting improved starting and operating of fluorescent lamps is proposed in U.S. Pat. No. 4,079,292 issued to Kaneda on Mar. 14, 1978. Therein, an oscillation booster circuit is utilized to provide reignition energy to a discharge lamp in each half cycle of an AC power source. Thus, a relatively small inductor ballast may be utilized in conjunction with a relatively high voltage discharge lamp. However, auxillary booster oscillator circuitry as well as the switching circuitry associated therewith are obvious disadvantages in so far as apparatus cost are concerned.
Additionally, U.K. Pat. No. 2,066,801 A published July 15, 1981 and issued to TDK Electronics Company, Ltd. suggests a non-linear dielectric element, the composition thereof, and a circuit utilizing the device with a lamp and a relatively complex preheating circuit for starting a lamp. Primarily, fabrication of this non-linear dielectric element is discussed and claimed.