Leading Edge Dimmer vs Trailing Edge Dimmer

Dimmers allow you to dim the room lights and create the mood to your desire setting. How the dimmer work is that it act as phase control or phase cutting by chopping out parts of the voltage and reducing power to the light source. There are two types of phase control dimmer available in the market that is Trailing-edge dimmer and Leading-edge dimmer.

Both of this dimmer type can dim convention lights like incandescent lighting. But how about LEDs? Which dimming type is suitable for dimming LED Light sources?

Leading Edge – Triac Dimmer

Leading Edge Dimming where it cut off the front edge of the half cycle as the AC waveform begins right after it crosses zero. Leading Edge Dimmer (also know as TRIAC dimmer) is typically used with incandescent bulbs, and produces a rush of voltage every half cycle, resulting in a rush of current to the light source.

Leading Edge Dimming

Leading-edge dimmer are cheaper and simpler than trailing-edge, and were used originally to dim incandescent and halogen bulbs or magnetic low voltage transformers. The leading edge dimmers use a ‘TRIAC’ (Triode for Alternating Current) switch to control power, and are sometimes called TRIAC dimmers.

They have much higher wattage range suitable for incandescent and halogen lighting (typically between 400W and 1,000W). Many existing leading-edge dimmer have a relatively high minimum load, which often can cause problems if they are used with LED lighting circuits. If the total loads of the particular LED lighting circuits is too low and there will likely be flicker, and possible noise like buzzing sound when dimmed.

Our Zero 88 dimmers are Leading edge type.

Trailing Edge – Electronic Dimmer

Trailing Edge Dimmers (electronic dimming or Reverse phase dimmers) cut off the second half of each half cycle as the AC waveform ends right before it crosses zero. This type of dimming is typically used with electronic drivers, and does not result in a rush of voltage (and a rush of current) to the light source.

Trailing Edge Dimming

Trailing-edge dimmers are more sophisticated and more expensive than leading-edge dimmers. They have several advantages over leading edge dimmers including smoother control, soft start and silent running when in operation. A trailing-edge dimmer has a lower minimum load than leading-edge dimmers, making it a better choice for dimming modestly sized low-powered lighting circuits.

Both types of dimmer can work with dimmable LEDs however due to its advantages, trailing edge is the preferred and as such LED manufacturers have designed their retrofit lamps to be compatible with trailing edge dimmers.

Looking into the future Trailing-edge dimmer are more popular choice for the LED light sources. Trailing-edge dimmers use a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or IGBT (Insulated Gate Bipolar Transistor) switch rather than a TRIAC and coil. This gives them their much-smoother dimming control, with no buzzing noise.

Our iLight dimmers are trailing edge dimmers.

Using Leading Edge Dimmers With LEDs

Many Leading Edge Dimmer have high minimum load requirements and you can struggle to meet this minimum with LED lamps and their low power consumption. Because of this you have to loops more LED lamps in one circuits to one dimmer in order to meet the minimum load requirements otherwise the LEDs lamps will flicker. The trick is to add one filament bulbs at the end of the circuit might solve the problem.

Using Trailing Edge Dimmers With LEDs

The 10% rule is very important when using trailing edge dimmers with LEDs. For example if using a 400W trailing edge dimmer may be able to power 400W of incandescent lamps with ease but when dimming LEDs the maximum load is only 10% of 400W. This means, with our 400W dimmer example, the maximum load would only be 40W worth of LEDs.

LEDs Dimming

Unlike incandescent bulbs, which are all dimmable by default, LED retrofit bulbs have a built-in driver in their base. The driver converts AC power to DC power and maintains a constant current to the LED. Some LEDs bulb come with builtin dimmable driver and some are not.

LED fixtures such as downlights usually include a separate LED driver, either of a ‘constant current’ or ‘constant voltage’ type, depending on the LED array design. Some dimmable LED downlight with LED driver can accept either Leading edge dimming or trailing edge dimming.

However, LED compatibility problems can exist, and some dimmable LED driver designs will only work with selective dimming control systems. These problems can show up in a number of ways including flickering, flashing, and shut off. If you’re shopping for dimmable LED light bulbs to replace the current incandescent bulbs, it is absolutely crucial that you ensure your bulbs and dimmer switches are compatible with each other to prevent this issues.

Contact Us to find out more of our trailing edge dimmers and leading edge dimmers.

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