The Basics: Dimming

Why is dimming used?

Energy savings

  • Daylight regulation – use of sunlight
  • Occupancy control – lights on only when needed in smart scheduling
  • Task tuning – using the right level of light
  • Load shedding – flexible energy use


  • Optimal light for task/scene – personal control
  • Comfort and safety
  • Ambient design


Dimming LED

If dimming is required, PWM (Pulse Width Modulation) devices drive LED’s at their rated current in a variable pulse.

  • For constant current drivers, these are always integrated.
  • For constant voltage driver systems, these are in some cases integrated, however the system may require a remote PWM interface.

PWM controls the time averaged current through an LED, and therefore, the brightness of the LED source or sources. In the PWM method, LED current level is set and then turned on and off very quickly, typically faster than is perceptible by the human eye. The dimming of the LED is proportional to the duty cycle of the PWM waveform.


The Common Dimming Protocols… (there are 4)

1) Phase Control

Leading Edge

Forward phase-control dimmers (also known as Leading Edge dimmers) control the amount of voltage available to a light source. The dimmer turns off part of the trailing edge of the AC sine wave for a pre-set amount of time, resulting in reduced lamp output (dimming).

Trailing Edge

Reverse phase-control dimmers (also known as Trailing Edge dimmers) control the amount of voltage available to a light source. The dimmer turns off part of the trailing edge of the AC sine wave for a pre-set amount of time, resulting in reduced lamp output (dimming).




2) 0-10V & 1-10V Analogue

The first and simplest electronic lighting control signalling system. Using a low voltage 0-10V DC signal connected to each LED power supply or Fluorescent ballast. At 0 volts the device will dim to 0% which will turn the device off, at 10 volts the device will be operating at 100%.

1-10V is also available. As stated 1Volt – 10Volt indicates this will only dim to 10%. In this system each light or circuit of lights would require an external switch to turn the light completely off.

Analogue dimming is considered “unidirectional” i.e. there’s no feedback from the interface device or ballast.


3) Digital Protocol: DSI

Digital Serial Interface, the precursor to DALI dimming systems uses a digital signal to DSI compliant devices, LED interfaces or electronic Fluorescent ballasts. This protocol is unique to Tridonic only.


4) Digital Protocol: DALI

Digital Addressable Lighting Interface (now the most commonly utilised commercial lighting control system). This is non-propriety lighting protocol, in that DALI is available from many different suppliers.

Digital protocols can be “bi-directional” i.e. devices or lighting fixtures can exchange data or communication back through the system. This could be data on faulty lamp reports or the use of sensors to communicate to lighting directly or in groups. NB: This is not possible with a DSI system.

Each DALI device has a “non-volatile” memory which contains it’s own settings such as an address, group assignments, scene levels and fade rates. This capability allows a DALI to operate with and without a central control point.




Other (less commonly used) protocols:

Switch dimming – this is a stand alone digital dimming protocol. It’s commonly used in residential or hospitality systems. It’s a cheap solution for dimming signal fixtures (i.e. a single fluorescent fixture) as there’s no control system required.

DMX512 – DMX512 is a digital communication protocol used commonly in the stage lighting and effects industry. It’s more commonly used in the commercial lighting market to control RGB and RGBW (white) colour change lighting systems.

DMX512 system allows for complicated programming to communicate to DMX devices through a ‘Data Bus’. This digital communication is sent generally in a 8/16bit code packets instructing fixtures on everything from dimming levels to movement positions.




For RGB we address each colour individually via a “channel”. By mixing these channels we can create multiple colour effects. With all colours at 100% this effectively creates white.

With RGBW, the white allows for each colour to be altered within its “hue”.






For more information please contact us.