The present invention relates to energy conservation dimmers for use on fluorescent lamps.
Fluorescent lamps, like fluorescent lamps and sodium vapor lamps, are a common feature today in commercial, industrial and increasingly in residential applications. A typical fluorescent lamp requires about a third or less of the electrical power of an incandescent bulb to produce the same amount of light and generally has a longer working life than an incandescent bulb. The efficiency of fluorescent lamps makes them an obvious choice for reducing lighting costs.
Coupled with the increased demand for fluorescent lamps was the demand and development of light level control devices which would allow users to reduce light output and power consumption when maximum illumination from the lamps is not needed. Despite the numerous improvements that have been made to such dimming control devices, current dimming technology is still unable to efficiently match the reduced light output with a corresponding reduction in power consumption. As a result dimmed fluorescent lamps often use more power than is necessary to maintain light levels at less than maximum illumination.
A significant period of inefficient power use occurs during the initial startup of the lamp. Generally fluorescent lamps require time to warm up before they reach full effectiveness. If the illumination is set to less than maximum during this time, the lamp will take longer to heat up and will use more power to do so. This limitation has been recognized in the prior art which have put forward several solutions to this problem, but generally circumvent the problem by inhibiting the dimming control during the lamp start-up phase. However, there are further energy-saving control steps that may be taken.
Prior art dimmer controls and ballast were often large circuits or systems. Multiple lamps were controlled by a central processor because the electronic circuitry for controlling an individual lamp was large and expensive. Many systems used microprocessors to control the lamps. Prior art systems also used inductors to limit the current in the lamps. Fluorescent lamps are negative resistance devices. Once they turn on, their resistance decreases. In order to limit the current in the lamp circuit other use inductors. But inductors are inefficient and waste power through heat.
Electronic ballast operates at a high frequency of 20-60 kHz whereas the conventional magnetic ballast operates at 50/60 Hz. The high frequency operation of the fluorescent lamp improves the efficiency by approximately 10 percent because of the increase in phosphor excitation. Flicker is also eliminated. Instant start is possible even at low supply voltage. Lamp life time is hence extended because coating of the filament can last longer.
Electronic ballasts operate at frequencies in the range of tens of kHz. By controlling the frequency, the power applying to the lamp is varied and hence the luminous output can be adjusted. Dimmable electronic ballast uses a low DC voltage or a rheostat to adjust the light output. It is typical to dim a lamp down to about 10 percent of its full brightness.
The present invention seeks to reduce the inefficiency of dimming control of fluorescent lamps by providing a more effective energy saving dimming control circuit. The invention also provides a relatively small control circuit that may fit into a standard two gang electrical junction box that is commonly used to hold an electrical receptacle or switch.