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KNX vs Dali vs DMX Lighting Protocol

When it comes to choosing a lighting protocol for designing a Lighting Control System (LCS) we are often left confused on which is the best, reliable, scalable, feature rich, future ready and cost effective protocol. To start with based on above parameters we have narrowed down this discussion to three widely used protocols in the lighting industry which are (a) KNX (b) DMX and (c) Dali. All three protocols are scalable and were developed between years1990 - 99 for different application in lighting industry for the purpose for automation.


 

KNX Protocol

Building automation protocol


KNX protocol is developed by KNX association with the aim of integrating & controlling multiple systems such as heating system, lighting system and access control systems in a building through central computer. More than 500 manufacturers around the world have developed KNX based devices across HVAC industry, Lighting industry and Security industry. Since with a KNX based systems there is a guaranteed forward and backward compatibility of products on the existing bus network, it becomes easy for the system designer to choose quality based devices or replace them with devices from other manufacturers in case devices are defective by design or run out of stock.


KNX System Architecture


System Overview


KNX is a decentralised system i.e. if one device stops working, the rest will continue to function unhindered. KNX is a wired system in which all KNX devices are connected to the KNX Bus Line. KNX systems consist of 5 components i.e (a) KNX Power supply (b) KNX Bus Line (c) Actuators (d) Sensors (e) IP Interface


(a) Power supply

This is a special KNX power supply unit that powers the KNX Bus Line so as to maintain a reliable connection between all devices.

(b) KNX Bus Line

Most simplest form of KNX Bus Line is Twisted Pair (TP) or 2 core cable. In KNX TP the bus cable supplies all bus devices with both data and power.

(c) Sensors

These are human interface devices such as switches, rotary dimmers, touch pads, thermostat touch panel, fingerprint scanner etc. which take input from direct human interaction and pass this message to the Actuators via KNX Bus Line.

(d) Actuators

Actuators are KNX controllers which are connected to KNX Bus Line and Appliances. They are responsible for controlling the functioning of connected appliances such as lights, fans, AC, projector, blinds etc.

(e) IP Interface

It is a KNX device that is connected to your WiFi router and KNX Bus Line. Through this device KNX system integrators program all Sensors and Actuators via ETS software.


Demerits

  1. Special KNX licensed system integrators are required to install and program the system via ETS KNX proprietary software. So any time you need to change configuration or if any device is replaced then you will have to call the KNX system integrator.

  2. KNX does not provide integration with Home automation standards such as Apple HomeKit, Google Home or Amazon Alexa. Third party services needs to be used.


 

Dali Protocol

Home lighting protocol


Dali is successor to 1-10v drivers for residential and small scale commercial lighting, it is the most widely used wired home lighting protocol. Dali main function is to group lights, dim the brightness and tune the colour of lights upto 2 channels. Dali had interoperability issues between devices of different manufactures, but Dali-2 has solved this problem where every manufacturer has to certify his device via a third party test laboratory to use Dali-2 logo on devices, again all Dali devices can be operated with Dali-2 devices.


Dali System Architecture

System Overview


Dali is a semi centralised system i.e. if one device stops working, the rest will continue to function unhindered, but still the complete system depends on Dali Controller. Dali is a wired system in which all below Dali devices are connected to the Dali Bus Line, similar to KNX. Dali systems consist of 5 components i.e (a) Dali Power Supply (b) Dali Line (c) Dali Controller/Bus (d) Ballast (e) Sensors


(a) Dali Power Supply

It powers the Dali Line so as to facilitate communication between Ballast, Sensors and Dali Controller.

(b) Dali Line

Dali Bus line is a 4 or 5 core cable (Line, neutral, earth optional and two control wires). A DALI line can be connected to a maximum of 64 DALI type Ballast. Dali control wires can be used along with mains line without any signal interference.

(c) Dali Controller / Bus

Dali controller is like device which can program the Dali Ballast via usb or IP interface or directly via a touch panel.

(d) Ballast

Dali ballast are devices or appliances controllers which control the power and functioning of the appliances such as bulbs, down lights etc.

(e) Sensors

These are human interface devices such as switches, rotary dimmers, touch pads and scene controllers which take input from direct human interaction and pass this message to the Dali Controller.


Demerits

  1. Dali has single point of failure i.e. if the Dali Controller / Bus fails then all Ballast and Sensor connected to it will stop working

  2. As Dali is an open source protocol it can be manufactured without any certification, hence they are difficult to commission.


 

DMX Protocol

Lighting & Effects protocol


DMX512 is the most famous, robust and widely used lighting and effects protocol in the market. Manufacturers can produce devices based on this open source protocol without getting any kind of certification. Originally developed for stage lighting and control, with advent of Artnet it has now moved to interior architectural, billboards, stadium and concerts lighting.


DMX512 System Architecture

System Overview


DMX512 is a centralised system i.e. the system is controlled by Master Controller. In this system all lighting fixtures or their decoders are daisy chained and addressed serially, wherein only the first lighting fixture is connected to the DMX Master. DMX systems consist of 4 components i.e (a) DMX Master Controller (b) DMX Universe (c) DMX Decoder (d) Lighting fixture


(a) DMX Master Controller

This is also known as DMX Console which is the heart of DMX system. It is where humans interact with the system via a computer or touch panel to control the lights.

(b) DMX Universe

Three wires (data + , data - and common) are used to connect all DMX Decoders to a single DMX Master via daisy chain connection method as shown in the above figure, this is called as single DMX Universe. In a single universe 512 control points are available i.e. 512 lighting fixtures can be turned on or off.

(c) DMX Decoder

Decoders are of different type depending on the lighting fixture they are designed to control. They process DMX Master signal and control the attached lighting fixture.

(d) Lighting fixture

Spotlights, RGB strip lights, focus lights, laser lights with 360 degree rotation on 2 axis etc.


Demerits:

  1. Centralised system has single point of failure i.e. DMX Master

  2. Daisy chain point of failure, if a single decoder fails or is removed from the chain then the decoders after that will stop working

  3. Sensor integration not available directly


 

Which one is better ?

KNX vs Dali vs DMX


Although each protocol was designed to fit for different applications initially, but due to advancement in microprocessor industry these protocols have invaded each others space, hence it is possible to compare them on certain common parameters discussed below.

PARAMETER

KNX

DALI

DMX

System architecture type

De-centralised

Semi-centralised. Since depends on Dali Controller /Bus

Centralised since depends on Master Controller

Communication

Bi-directional. Hence health of devices could be known

Dali is unidirectional while Dali-2 is bidirectional

DMX is unidirectional. DMX RDM is bidirectional

Fault finding of devices possibility

Yes

no

no

Manufacturer device certification required

Yes, devices need to be certified by KNX labs/association

Dali, not required. While Dali-2 requires certification

Not required

Compatibility of devices between different manufacturers

Yes. Ensured by certification.

No. Sometimes issue arises between different manufacturers.

No

System Integrator requirements

Should be certified by KNX

No such requirement

No such requirement

Programming or changing configuration

Requires ETS software and System Integrator

Can be changed via controller, no expertise required.

Can be changed via controller, no expertise required.

Number of devices on single bus line

256

64

512

Communication rate

9600 bps

1200 bps

250,000 bps

Other system integration

Yes. Such as HVAC, Security, Energy Management

No. Limited to lighting only.

No. Limited to lighting only.

Extreme lighting effects

No

No

Yes

Security

KNX Secure

No

No

Cost

KNX Direct less cost

Dali gateway higher cost

Low system cost compared to both

Application

Building automation, Lighting automation, Commercial automation, Energy management.

Lighting automation for small scale projects. Such as home lighting or shop lighting.

Stage lighting, theatre lighting, billboards, signages, building facade lighting. Multi coloured effect lighting.


Conclusion

For any wired lighting project where scalability is required it is suggested to use KNX system. For lighting projects where colour effects with synchronisation is a necessity or for small scale interior architectural projects, it is recommended to go with DMX Lighting. Dali or Dali-2 is not recommended for medium or large scale lighting projects unless existing system is based on Dali protocol and has Dali to KNX gateway. Dali is recommended for small scale lighting projects where the complete ecosystem i.e. Dali bus controller, scene controller, sensors, lights, switches and power supply are from same manufacturer and client wants to change the system configuration anytime on his own without depending on any system integrator.

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