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
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.
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
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
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:
Centralised system has single point of failure i.e. DMX Master
Daisy chain point of failure, if a single decoder fails or is removed from the chain then the decoders after that will stop working
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.