A lighting control system is used mostly for the control of the lights in public facilities, and they can either become a standalone system or a subsystem of the building automation system. In which case, why not just just the DDC for controlling the lights as well.
The focal point of a building automation system is the control center. But in a lighting control system there can be both a centralized control and local control, in some cases, local control can even have multiple access points and even scene recall capability.
To further elaborate:
- Local digital switches have status feedback
This is one of the more prominent features of the local switches of a lighting control system. Having local control and scene recall is a very basic requirement of a lighting control system, this is demonstrably a feature that cannot be performed by the administrator at the control center. Lighting control is a control system that requires both local and central dual control. - For small scale applications, simply use digital switches
Such applications often does not require the involvement of a computer based central control system, where one can simply use either the multiple digital switches or a touch panel as the user interface for centralizing control of all the lights. Such a setup is inexpensive, easy to implement, simple and convenient to operate. - For medium scale applications, one can implement a standalone central control system, and also integrate it into the BAS.
The D-Bus lighting control system has an open Modbus protocol that can be used by the graphical control software on a host computer to interface with; of course, the BAS software can use this to interface with the D-Bus lighting control system as well. - For large scale applications, it is strongly recommended that one have a single centralized point of control. Otherwise, there would be far too many touch panels distributed all over to control the lights in various areas. It is further recommended that there should be a second duplicated central control in case the first one fails.
- Cost and backup considerations
Even if only the central control is implemented without any local controls, the cost is still much lower than that of a BAS. One should also consider that when the central control host fails, then there must be some form of backup control, on this point, it is also easier to implement this in a lighting control system and the cost is also much lower. - Lighting is a high voltage system
(hardware wise it is inadequate, because of small relays, colossal engineering cost, multiple wires)
A BAS specializes in central HVAC control and the safety system, while a lighting control system specializes in lighting control. Even though a BAS can be used for lighting control, doing so is clumsy and expensive, since each control point needs to have its own contactor and wiring, all the wiring combined will result in a mass of wires snaking from panel to panel.
Contrast this approach with a dedicated lighting control system wherein the hardware components are designed specifically for lighting. Which results in simplified engineering work and greatly reduced costs.
If the building does not have central HVAC, but instead uses local air conditioners such as box types or split type air conditioners, or if they don’t have any air conditioners at all, then the BAS would be used exclusively on lighting and its strong suite would be completely wasted. In which case why not simply use a dedicated lighting control system in the first place. - Combining monitoring with control makes things more direct and reliable.
The most expensive hardware portion of a BAS is the DDC, and since it is a low voltage system; every lighting load that it needs to control would be through its DO ports controlling the intermediate magnetic contactors. While the status feedback would return to the DDC through its DI ports.
In contrast, in a dedicated lighting control system, the controller and the relay is combined together and there is no need for an external magnetic contactor,
In a lighting control system, the load control and feedback are combined into the same unit. The wiring is more straightforward and there is no need for any separate DI ports for the feedback signal. There is also no need to perform any sort of special programming as all the logic is already built into the unit.
In a BAS, all of these are considered as separate and extra material, panel wiring and programming costs. Of course, all of these costs is greatly reduced or obviated in a lighting control system, with the additional benefit of less space occupied.