There are several alternative approaches to dimming LEDs that apply in different segments of the market. But legislation eliminating incandescent lights make it inevitable that dimmable LED products will eventually dominate the market.
Some early LED bulb replacement products are not dimmable. of Energy has mandated such capability for any lamp hoping to gain an Energy Star rating.
#Electronic dimmer for led lights drivers#
One reason dimming capability is important for LED drivers is that the US Dept. Either dimming technique described above will extend the L70 parameter by operating the LED at reduced output. Lumen maintenance for LEDs is specified by the L70 parameter, which indicates the average hours of operation until the light output deteriorates to 70% of its initial quantity. Dimming reduces both of these parameters and thus potentially extends LED operating life. It is worth noting that the operating life of LED light sources depends on the operating temperature and current that the individual LED die see. However, this technique causes some white LEDs to change color and is more difficult to control at low dimming levels. Alternatively, LEDs can be dimmed by reducing the dc current. The PWM dimming frequency must be above 120 Hz to comply with Energy Star requirements by avoiding visible flicker. This action adjusts the average current, which is proportional to the light output. So LED dimming can use pulse width modulation (PWM), in which the output current is switched on and off at a constant frequency with a variable duty cycle. LEDs, unlike discharge lamps, need no high-voltage ignition. Off-line LED drivers are comprised of constant-current regulating switching power supplies generally equipped with dc outputs. This constitutes a stable load that can be driven by a constant dc current source. LEDs consist of a solid state p-n junction with a fairly constant forward voltage drop. In contrast, it is much more straightforward to dim LEDs because of their makeup. This forces dimming circuitry to include a closed-loop current regulating system able to respond rapidly to such changes. In addition, there are operating points at which lamp impedance changes rapidly in response to small changes in arc current. One reason they are so hard to dim is that the impedance of plasma arcs is non linear and varies considerably depending on current and temperature.
Instead, they use specialized dimming controllers, often demanding additional analog or digital dimming control cables.įluorescent and HID lamps are both types of arc discharge lamp. To further complicate matters, most dimmable fluorescent and all HID systems are incompatible with standard triac-based phase dimmers. Dropping past that point risks experiencing noticeable color change and instability in their plasma arc. But even with electronic ballasts, HID (high-intensity discharge) lamps cannot be dimmed to much more than half of their maximum light output. With relatively expensive dimmable electronic ballasts, fluorescent lamps can be dimmed to below 5% of maximum light output. Consider, for example, fluorescent lamps. International Rectifier, The quest for energy efficiency has led manufacturers to investigate ways of dimming all kinds of lighting technologies, including those that usually can’t be dimmed.