DIMMING EXPLAINED

0-10 (Analogue) Dimming

0-10 V is one of the earliest and simplest electronic lighting control signalling systems; simply put, the control signal is a DC voltage that varies between zero and ten volts. The controlled lighting should scale its output so that at 10 V, the controlled light should be at 100% of its potential output, and at 0 V it should at the lowest possible dimming level

Dali Dimming

DALI stands for Digital Addressable Lighting Interface. It is an International Standard (IEC 62386) lighting control system, providing a single interface for all electronic control gear (light sources) and electronic control devices (lighting controllers).

The DALI Standard enables dimmable ballasts, transformers, relay modules, emergency fittings and controllers from different manufacturers to be mixed and matched into a single control system.

A DALI system provides designers, installers, building owners, facility managers and end-users with a powerful and flexible digital lighting system, with compatibility of supply from many sources.

Mains Dimming

This will be familiar to many people, as it’s the method generally used in homes. Mains dimmers tend to be rotary and are what you would find on a wall in place of a light switch. They have a knob you can twist anticlockwise or clockwise to decrease or increase the light output and push in to switch the light on and off.

Mains dimming works by chopping up the electrical signal from the mains. It does this by switching the electric current on and off several times a second. The result of this rapid switching is that less power is available to the light as the power is off for part of each second.

The light is on and off at full power, but less light is delivered in total compared to if it was on the whole time. Since our eyes cannot process the rapid switching, our brain interprets this as a steady, dimmed light source.

The power from the mains in the UK comes in a wave with a frequency of 50Hz. That means this wave is repeated 50 times a second. As the current from the mains is alternating, switching from positive to negative every cycle, there are 100 cycles of current per second: 50 positive and 50 negative.

Mains dimming is achieved by switching off the power for a period twice in every wave, one for each cycle of current.

Mains dimming can be split into two types – Leading Edge and Trailing Edge

Leading & trailing edge dimming

Before LEDs, we used to dim halogen lamps with wall dimmers.  We can still use these kinds of dimmers.  But dimmer, driver and LED-module must be compatible with each other.

This type of control is accomplished without any need for an additional control wire. It involves connecting a dimmer in series between one of the mains wire and the equipment.

The dimmer cuts part of the mains voltage sinusoidal waveform to a greater or lesser extent in order to dim luminous flux even from 1% to 100%  (this value depends on dimmer and driver).

Depending on how the driver makes the mains voltage cut, it is possible to distinguish between two types of dimming:

Leading Edge Dimming

Trailing Edge Dimming

Leading Edge Dimming

Dimming cut-off in the wave on its ascending side, from the beginning (phase cut-off at ignition). This is traditionally used in halogen lamps supplied through electromagnetic transformers.

Trailing Edge Dimming

Dimming by cut-off in the wave on its descending side, from the end cutting backwards (phase cut-off at switch off).  And this way of dimming causes less interferences than leading-edge dimming. There are dimmers and equipment that support both types of dimming, and others that support only one type.