LEDApplicationSeriesDimmingLEDs-Conservation.pdfVIP

LED Application Series: Dimming LEDs LED Application Series: Dimming LEDs Lack of effective and affordable dimming has hampered the adoption of CFLs in the residential sector. LEDs are in theory fully dimmable, but are not compatible with all dimmer controls designed for incandescent lamps. What are the prospects for dimming LEDs in residential applications? Standard dimming controls Typical residential incandescent lamp dimmers are essentially electronic switches that toggle on and off 120 times per second. By delaying the beginning of each half-cycle of AC power (known as “phase control”), they regulate the amount of power to the lamp filament. Because this occurs so quickly, most people do not detect flicker, but see continuous dimming. Although the general operation of such electronic dimmers is the same, the specific electrical characteristics of residential dimmers can vary considerably. These variations are immaterial to incandescent lamps, but matter greatly when used with electronic devices such as compact fluorescent lamps (CFLs) and LEDs. Alternating current (AC) wave form, showing one complete cycle. AC cycles at 60 hertz, or 60 times per second. Typical household dimmers switch off the current twice per cycle, or 120 times per second. Dimming CFLs Some screw-in (integral) CFLs can be dimmed using line-voltage incandescent dimmers but must be specifically designed to do so. They typically dim only to about 20% of maximum intensity, due to limitations of the low-cost ballast. More sophisticated electronic ballasts providing continuous dimming below 5% are available, but are simply not cost-effective for use in screw-in CFLs. Some fixtures (e.g., torchieres) successfully use pin-based CFLs in combination with on-board dimming controls. Four-pin CFLs using separate dimming ballasts can be dimmed via line voltage or 0-10 volt DC control, with dimming range as low as 1%, but more commonly 5% or 20%. Will LEDs solve the dimming problem? LEDs face a dimming cha