How to choose leading edge dimmer or trailing edge dimmers for LED?

Dimmers allow you to achieve the exact light level that you desire in a room and consequently alter the mood. There are various types of dimming control devices available, but the most popular are ‘phase control’ (or phase-cut) dimmers.

The two types of phase control dimmer available are ‘trailing-edge’ and ‘leading-edge’. These two different types work in different ways.

Because they work differently, this ultimately affects their compatibility with certain light forms:

  • Leading-edge: inductive loads (e.g. magnetic low voltage transformers), resistive loads (e.g. incandescent).
  • Trailing-edge: capacitive loads (e.g. electronic low voltage transformers, LED drivers), resistive loads (e.g. incandescent).
dimmer switch

There are also other differences between the two types of dimmers…

Leading-edge dimmers (TRIAC dimmers)

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

Many existing leading-edge dimmer switches have a relatively high minimum load, which often rules out their use with modest LED or CFL lighting circuits. However, leading-edge dimmers are by far the most common dimming control in existence.

Trailing-edge Dimmers (Reverse phase dimmers)

Trailing-edge dimmers are more sophisticated than leading-edge dimmers, and usually use a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) or IGBT (Insulated Gate Bipolar Transistor) switch rather than a TRIAC and coil. This benefits the user with smooth, silent dimming control, absent of any buzzing noise.

A trailing-edge dimmer has a lower minimum load (often 10W) than leading-edge dimmers, making it a better choice for dimming modestly sized low-powered lighting circuits.

Particularly beneficial for incandescent and halogen bulbs is the ‘soft start’ feature in trailing-edge dimmers, which prevents filament bulbs from dying or exploding of thermal shock when first switched on.

How to avoid LED dimmer compatibility issues?

For an LED lamp or luminaire to be functional with a phase control dimmer, the electronics of its driver have to be compatibly adapted.

Leading-edge dimmer switches are sometimes called ‘incandescent dimmers’, because they were originally designed to handle the resistive load of incandescent light. Existing dimmer switches tend to have high minimum loads and may require multiple LED lamps in order to even have a chance of working.

Maximum loads in a leading-edge dimmer also tend to be invalid with LED retrofit lamps or fittings. Dividing the maximum load by 10 to calculate maximum LED load is a commonly used rule of thumb.

For an increased chance of compatibility, trailing-edge dimmer switches tend to work better with the capacitive load of an LED driver.