The pros and cons of DALI for homes
DALI is well known as a commercial lighting control protocol that works perfectly with KNX. The question is why and how can DALI be used for residential lighting control?
Addressable DALI lighting is organised in lines, or ‘universes’, of up to 64 addressable DALI ballasts (connected to luminaries) that are each provided with a 230V and 2-wire control bus (made simpler with a 5-core cable), most often in a snaking daisy chain of up to 300m. If more than 64 lamps are required then multiple universes can be connected together with KNX being used as the backbone. To keep bus traffic light it is advised that sensors and other input devices are placed on the KNX bus. The DALI ballasts can be addressed individually, or in groups by the KNX-DALI gateway (so for instance a group of living area downlights can be operated together as a group).
For many years DALI has been an good solution for commercial projects like offices due to the flexibility and ease of installation, but was not used residentially due to the high cost and poor availability of DALI-ready luminaries. Over recent years the costs and choice of DALI fittings and ballasts has dropped dramatically making residential applications worth consideration. However it is not as simple as cost and availability, other factors must be considered before using DALI as an alternative to more traditional phase dimming.
Here I discuss some of the factors that should be considered:
- Simple topology - the DALI topology is simple, not requiring radial circuits from lamps circuits to the distribution board. Amongst other things this means a lot less copper.
- Less distribution board space required - one module provides control for up to 64 lamps, a density not possible with phase dimmers.
- Simple Board wiring - there is much simpler termination and cable management in the distribution board.
- DALI ballasts typically provide a very smooth dimming curve for LED lamps
- Flexibility for the future - once installed lamps can be re-addressed and re-grouped with software rather than having to rewire circuits. Also, if an additional lamp is required after the project is complete it can simply be added to the DALI bus and provide with 230V rather than running a new 230V radial to a dimming actuator in the distribution board.
- As DALI and lighting design evolve to incorporate the wellness benefits of tuneable white (human centric lighting) the control can be adapted without any change to the wiring already in place.
- Cost equation does not balance - If a reasonable number of circuits is being considered then there is less cost in the distribution board but the luminaire/ ballast cost is still higher.
- Not as simple to commission - do not underestimate the added complication of addressing and configuring the DALI groups (largely sorting out addressing of the ballasts). This will take added configuration and commissioning time.
- Not as simple to test and fault find - as the ballasts are software controlled they are harder to test and debug for an on-site electrician. Challenges of networks and component fault finding should not be underestimated
- DALI is not a standard - as DALI is not a standard, unlike KNX, there is no guarantee that all products will play together. Most times it is OK, but the one time it is not will be expensive to fix.
- DALI is a ‘send and forget’ protocol, so telegrams are not acknowledge as received. So, if a control telegram is sent to a ballast to turn on a light and there is a collision with another telegram there is not failsafe for the light to in fact turn on (the converse is true of KNX).
Installers must decide on a case by case basis whether DALI is the right solution for a project, but it may well form part of a blended technology for the lighting control that might include, phased, DALI, 1-10V and DMX depending on the lighting designer. Also consider that the sensors in a project (keypads, motion sensors) are best on the KNX side of an installation for reasons of data traffic, and functionality, so, with this in mind the non-DALI lighting control may also be directly KNX controlled with direct KNX-DMX, KNX-1-10V or KNX-LED devices.
It is worth noting that recently we have seen many higher end residential installations successfully take the benefit of flexibility and great dimming and absorbed the addition costs of product and commissioning, with stunning results.
DALI certainly has its place in residential installations, but the pros and cons should be considered with eyes wide open.