Variable high frequency lamp controllers and systems

Details Variable high frequency lamp controllers and systems Variable high frequency lamp controllers and systems

2000-01-26

2001-05-08

Philogene, Haissa (Department: 2821)

Electric lamp and discharge devices: systems

Current and/or voltage regulation

C315S2090SC, C315S226000, C315S278000, C315S244000

Reexamination Certificate

active

06229270

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to the control of gaseous discharge lamps, such as fluorescent lamps, and more particularly to the adjustment of the intensity of their light output.
BACKGROUND OF THE INVENTION
Fluorescent lamps have been the commonest method of lighting consumer, commercial and industrial areas for many years. In operation, a gas mixture enclosed in the glass tube of the lamp is ionised by means of a high voltage pulse applied between two heated electrodes at each end of the tube. In a conventional lighting system, the gas in the fluorescent tube is extinguished and then ionised again with each half cycle of the 50 Hz conventional line frequency. This system has the merit of low capital cost and simplicity, but whilst far superior to incandescent lamps in the conversion of energy to light, it is nonetheless an inefficient mechanism. The circuit watt losses are similar whatever the wattage of the lamp and range from about 66% for an 18 watt lamp to 20% for a 70 watt lamp. In addition, the flicker caused by the re-ionisation of the lamp every half cycle at 50 Hz is now recognized as a major cause of headaches amongst office workers.
In consequence, a number of improvements have been initiated over the years to reduce the inefficiency and the flicker associated with fluorescent lamps.
An electronic controller addresses a number of these problems. It supplies the gases in the tube with a high frequency AC current, preferably above 18 kHz. This type of controller typically reduces circuit losses from the range 20-66% to the range 4-8%. Owing to the high frequency refresh rate of the lamp, its light output is increased. Accordingly, lamps are commonly under-powered such that the same output is produced as that resulting when running the lamp with a standard mains frequency circuit. For example:
Standard Circuit
Lamp wattage:
18 watts
Circuit losses:
12 watts
Total power consumption:
30 watts
High Frequency Circuit
Lamp wattage:
16 watts
Circuit losses:
 2 watts
Total power consumption
18 watts
The lumens output of each lamp in the above example would be identical.
The use of a high frequency controller is also beneficial as the refresh rate of the lamp is effectively 60,000 a second when running at 30 kHz, for example. Therefore, there is no flicker detectable by the human eye. Also the electronic controller unit can be less than half the weight of a standard circuit, and generate less heat. An electronic controller is also more versatile. For example, it can be interfaced with passive infra-red movement detectors or optical sensors which detect ambient light levels.
It is generally desirable to include a dimming facility in a lighting system, as the required lighting level may vary depending on various factors. For example, an office may be converted to intensive computer use, and a lower level of lighting is then appropriate owing to the relative dimness of a computer screen. Also, it has been found that the light tolerance and the amount of light needed or felt to be needed for given tasks varies greatly between individuals. In particular, it varies considerably between different age groups. 50-60 year olds will require substantially more light for the same range of tasks as 18-25 year olds. In addition, the light required within open plan and cellular offices varies greatly according to the type of partitioning system, colours and furniture used. Furthermore, office layout designs are changed frequently and in large organisations this can affect as much as 20% of the office space per annum. In consequence the original lighting can be either too bright or too dim in the revised spatial layout.
The abstract of JP-A-01084596 describes control circuitry for a discharge lamp, in which a variable inductance is provided to control the light output of the lamp.
Various forms of dimmable high frequency electronic controllers are available which can reduce their operating wattage from 100% to about 5%. Typically, a wall mounted potentiometer operable by a user is provided to send a control signal to each controller. Each controller accordingly alters the current and frequency which powers the discharge lamps of the respective luminaire. However, such controllers are expensive, typically costing 60% more than a conventional electronic controller. Therefore, it is only worthwhile to link at least ten and usually at least twenty-five luminaires in the dimming circuit, such that light levels can only be adjusted over large areas and in a uniform manner. Furthermore, in such a configuration, wiring needs to be routed from the wall mounted potentiometer to each luminaire in turn to carry the control signal. Installing this wiring is a time-consuming process, particularly when refurbishing a building having existing partitions, fixtures and the like.
SUMMARY OF THE INVENTION
The present invention provides high frequency control circuitry for a plurality of gaseous discharge lamps, comprising a plurality of mechanically variable inductive reactance means, each reactance means being adapted to be connected in series with at least one gaseous discharge lamp to control the current fed to said lamp, the reactance means being adjustable by a user to alter the intensity of the light emitted by said lamp, and wherein each reacance means comprises a coil having a plurality of tappings spaced along its length and a switch for selectively connecting to one of the tappings, the circuitry further comprising a linkage connecting the respective switches of the reactance means such that adjustment of one switch produces a corresponding adjustment of the other switches.
Accordingly, the invention enables individually adjustable control circuits to be produced with little additional cost compared to a circuit without an adjustment facility. The additional cost may therefore be recouped relatively quickly through energy saving by dimming lights as necessary.
It may also allow the lighting level of individual luminaires to be varied above and below their standard fluorescent lamp wattage. Conversely, known dimming systems can only be used to reduce light levels from the standard wattage.
In a preferred arrangement, the circuitry includes a drive oscillator and the high frequency output of the drive oscillator is applied across a two-wire bus bar. A respective sub-circuit comprising starting means, constant inductive reactance means, variable inductive reactance means and output means is provided for each lamp, each sub-circuit being connected across the bus bar. The lamps are individually controllable, but are driven from one control unit with only the sub-circuit being replicated for each lamp.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:


REFERENCES:
patent: 5055747 (1991-10-01), Johns
patent: 5057570 (1991-10-01), Farrall et al.
patent: 5920155 (1999-07-01), Kanda et al.
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patent: WO84/02825 (1984-07-01), None
patent: WO90/05992 (1990-05-01), None
patent: WO91/13530 (1991-09-01), None

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