Phase cut-off and phase cut-on are two different techniques for dimming lighting. It is important to know which technique your lamp uses, as this determines which dimmer is suitable. Using the wrong combination? Then the dimming will not work properly.

Phase cut-on (leading edge / RL)

Phase cut-on – also called leading edge or indicated with RL – is an older dimming technique.

• Usually dims down to about 10% of the light level
• Mainly used with incandescent and halogen lamps
• Can sometimes still be found with LED lamps
• Well-known brands such as Philips regularly apply this technique

So pay close attention when choosing your lamps and dimmer.

Phase cut-off (trailing edge / RC)

Phase cut-off – also called trailing edge or indicated with RC – is the most commonly used technique in modern lighting.

Advantages:

• Full dimming range (often down to very low levels)
• Smoother dimming
• Quieter in use
• Almost no chance of buzzing noises

Most LED lamps on the market operate with phase cut-off.

What should you watch out for?

It is important that your lamp and dimmer use the same dimming technique.

• A phase cut-off lamp does not work well on a phase cut-on dimmer
• And vice versa applies

Fortunately, this cannot cause damage. The only consequence is that your lamps do not dim (properly).