Der neue EL5B mit PWM Technik
Restaurants and theaters have long employed dimming as a way to create atmosphere, foster a sense of intimacy, and transport diners and audiences alike. Dimming can reduce energy consumption and enhance a space’s function, as in the case of a seminar room or lecture hall. But despite their ubiquity, dimmers used with conventional sources can still have problems, including a reduction in efficacy for incandescent lamps, and a reduction in longevity for fluorescent lamps.
The majority of dimming systems installed today are phase control devices. Designed originally for incandescent lamps, they reduce light output by “interrupting the current during each AC [alternating current] half-cycle,” says Nadarajah Narendran, director of research at the Lighting Research Center (LRC), in Troy, N.Y., and program organizer of the Alliance for Solid-State Illumination Systems and Technologies (ASSIST) program. Essentially, phase control devices temporarily shut off power to the light source and dim voltage. In fact, they’re also called phase cut dimmers because the interruptions in current create cuts in the AC sine wave.
The interruptions occur at a rate of 120 times per second, or twice the frequency at which alternating current delivers electricity over power lines. But because the tungsten filament in incandescent lamps is slow to heat up and cool down, the human eye sees the output as a constant level of decreased brightness. The longer the interruptions, the dimmer the light.
Not all phase control devices cut from the same part of the AC sine wave. A triode semiconductor for alternating current (TRIAC), which is used to dim incandescent and halogen lamps, cuts from the forward phase, which begins just as the current changes polarity and the voltage running through the circuit is zero. Also referred to as forward-phase control dimmers, TRIACs can produce spikes in current that cause dimmed lamps to buzz and add stress to electronic drivers.
Reverse-phase control dimmers avoid these problems by cutting from the latter portions, or trailing edges, of the AC waveform. By switching the light circuit on just as the current changes direction, they allow the voltage to rise gradually before turning it off later in the half-cycle. Also called electronic low-voltage (ELV) dimmers, reverse-phase control dimmers were developed to enhance the performance of halogens that use electronic transformers.