Dimming LED

Ever changed your light bulbs and you get a disco effect when trying to dim? Or installed a dimmer only for it not to dim the LED lights at all?

Here we talk about about dimming LEDs with a basic explanation with some of the advantages and disadvantages of the various ways of dimming LED.

PS; Its not just a rotary dimmer!

Mains Leading/Trailing edge

The Basics: Comes in a variety of shapes and sizes. It requires standard main AC cable and in its simplest terms it dims the lights by chopping up the sine wave of the voltage.


  • Large number of manufacturers of dimmer units – making it a very mature technology with a variety of finishes.
  • Simple to implement.
  • No control system required.
  • Inexpensive.


  • Due to the fact that LEDs have comparably low loads to conventional halogen technology they are often incompatible with standard dimmer. Typically minimum loads should be above 10-30 watts to dim.
  • As a result can cause flickering, buzzing or premature failure if incompatible.
  • They don’t always dim  down to 0%
  • One way switching and no feed back.

Analogue 0-10v

The Basics: Analogue dimming typically requires 5 core, 3 core mains and a 2 core control or signal cable. It dims by varying the DC from 0-10, with 0 volts being 0% and 10 volts being 100%. You need a separate switch as the signal wont always dim to 0% (or off) It can be linked to a 0-10v switch or a control systems.


  • Robust, well understood technology which works well with LED.
  • Simple to diagnose if problems as you can test the voltage.
  • Low voltage so can run with low diameter cables.


  • Limited number of 0-10 dimmer manufactures which work well (so often a control system is required)
  • Difficult to combine 0-10 switch plates with mains dimming.
  • Not every one is familiar with the methodology.
  • Requires additional signal cable  -which can increase the cost.
  • Has no feed back.
  • Polarity dependent
  • Each circuit or device needs to be connected with the signal cable which for large systems can potentially be expensive.

DSI Digital Serial Interface

The Basics; Requires 5 core cable -live, neutral and earth and 2 control cable.  Dims via a digital signal.


  • Its simple nature makes it straightforward to understand.
  • Each device has its own wire to the contoller it has no need of an address to be set, so can be replaced simply by unplugging the faulty one and plugging in the new.
  • It dims to off, so does not require mains switching equipment to turn them off.


  • It requires one wire per control channel so a sophisticated system could have hundreds of wires, thereby making diagnoses of problems difficult.
  • Programing required.
  • Requires a control system

DSI is the basis of the more sophisticated protocol DALI.

DALI Digital Addressable Lighting Interface

The Basics; Requires 5 core cable. Dims via a digital signal.


  • Each lighting device is assigned a unique static address in the numeric range 0 to 63, making possible up to 64 devices in a standalone system.
  • Complex switching arrangements can be made from the system.
  • Has two way communication and will give status reports on the light fitting.
  • It dims to off, so does not require mains switching equipment to turn them off.
  • Reconfiguring lighting is easy as each is individually addressed – especially useful in open plan offices.


  • Can be expensive.
  • Requires programming to address each ballast.
  • Requires a central control system.
  • Requires a programmable ballast so even for a mains supply LED lamp will require additional interface to enable it to link to the system.
  • If the ballast goes it loses the address.
  • Needs to be updated if the function changes.

DMX  Digital Multiplex

The Basics; DMX has traditionally been used in the entertainment industry for control of coloured lighting but is used within architectural lighting as well. It is controlled with a digital signal as with DALI each unit has an individual address.


  • up to 32 devices can be daisy chained together
  • 5-pin XLR connectors with RJ45 cables.
  • Simple to implement
  • Very reliable and well understood technology.
  • Great for colour control


  • Requires programming to address each ballast.
  • Requires a terminator in the final loop of the DMX driver.
  • Not standard wiring  – more suited for entertainment electrical contractors.

These are meant as very basic guidelines for some useful information on choosing the most appropriate method of dimming your LED. There are many others control methods such as KNX or IP enabled devices which we havent listed. There are also many ways of dimming LED via your ipad or iphone; http://www.thelightingdesignstudio.co.uk/blog/lighting-control-with-iphone-ipad/

If you have any lighting control queries please get in touch with the lighting design studio.