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Electrical Blog: Leading Edge Dimmer vs. Trailing Edge Dimmer: Illuminating the World of Dimmers

Dimmers play a crucial role in setting the ambiance of any space by allowing you to adjust the intensity of the lighting. These devices function by employing phase control or phase cutting techniques, which involve chopping out segments of the voltage supply to reduce the power delivered to the light source. In the world of dimmers, two key players take the stage: Leading-edge dimmers and Trailing-edge dimmers.

While both of these dimmer types are well-suited for traditional light sources like incandescent bulbs, the real question arises when considering their compatibility with modern LED lighting. Let's delve into the intricacies of these dimmers and explore which type is better suited for dimming LED light sources.

Leading Edge Dimmer (Triac Dimmer)

Leading Edge Dimming involves cutting off the front edge of each half-cycle as the alternating current (AC) waveform begins, right after it crosses zero. Commonly referred to as TRIAC dimmers, Leading Edge Dimmers are typically associated with incandescent bulbs. They work by sending a surge of voltage every half-cycle, resulting in a surge of current to the light source. Leading-edge dimmers are cost-effective and straightforward, making them the go-to choice for dimming incandescent and halogen bulbs or magnetic low-voltage transformers. These dimmers use a 'TRIAC' (Triode for Alternating Current) switch to regulate power and are sometimes referred to as TRIAC dimmers.

One notable advantage of leading-edge dimmers is their high wattage range, making them suitable for incandescent and halogen lighting (typically between 400W and 1,000W). However, many existing leading-edge dimmers have a relatively high minimum load requirement, which can pose problems when used with LED lighting circuits. If the total load of the LED lighting circuit is too low, it can lead to flicker and potential noise issues, such as a buzzing sound, when dimmed.

Trailing Edge Dimmer (Electronic Dimmer)

Trailing Edge Dimmers, also known as electronic dimmers or reverse-phase dimmers, cut off the second half of each half-cycle as the AC waveform ends, just before it crosses zero. This type of dimming is typically employed with electronic drivers and does not generate a voltage or current surge to the light source. Trailing-edge dimmers are more advanced and relatively pricier compared to leading-edge dimmers. They come with several advantages, including smoother control, soft start, and quiet operation during use. Additionally, trailing-edge dimmers have a lower minimum load requirement, making them a preferred choice for modestly-sized, low-powered lighting circuits.

Both leading-edge and trailing-edge dimmers can work with dimmable LEDs. However, due to their advantages, trailing-edge dimmers are often the preferred choice for LED light sources. LED manufacturers have adapted their retrofit lamps to be compatible with trailing-edge dimmers, making it the go-to option for the future.

Trailing-edge dimmers employ MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or IGBT (Insulated Gate Bipolar Transistor) switches, instead of a TRIAC and coil, resulting in smoother dimming control with no buzzing noise.

Using Trailing Edge Dimmers With LEDs

When using trailing-edge dimmers with LEDs, the 10% rule is essential to keep in mind. For instance, if you use a 400W trailing-edge dimmer, it may easily handle 400W of incandescent lamps. However, when dimming LEDs, the maximum load should be no more than 10% of the dimmer's capacity. In this example, the maximum load for LEDs would be 40W.

LED Dimming

Unlike incandescent bulbs, which are inherently dimmable, LED retrofit bulbs come with built-in drivers in their bases. These drivers convert AC power to DC power and maintain a constant current to the LED. Some LED bulbs come with built-in dimmable drivers, while others do not.

LED fixtures like downlights usually include a separate LED driver, which can be of the 'constant current' or 'constant voltage' type, depending on the LED array design. Some dimmable LED downlights with LED drivers can accommodate both leading-edge and trailing-edge dimming.

However, LED compatibility issues can arise, and certain dimmable LED driver designs may only work with specific dimming control systems. These issues can manifest as flickering, flashing, or lights turning off unexpectedly. When shopping for dimmable LED light bulbs to replace incandescent ones, it is crucial to ensure compatibility between your bulbs and dimmer switches to avoid these problems.

In conclusion, while dimmers play a crucial role in enhancing the lighting experience, choosing the right type of dimmer for LED sources is critical. Trailing-edge dimmers, with their advanced technology and compatibility, are poised to be the preferred choice for LED lighting, ensuring that your ambiance is as smooth as your dimming experience.

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