simply Philips Hue light bulbs have all the logic within the bulb.
with KNX and other systems you have that seperated:
- the lamp - it just lights, dimms or changes Color
- and the controlling unit - it controls how the lamp works
so, if your lamp is defect - you just change it with a new one, the logic stays in the actuator. the Hue bulb is changed with its logic. Then you have the hue bridge, which is like the KNX bus and provides the API and the communication protocol.
I know nothing on Modbus, so I’m not the best to answer this. But I can imagine, using modbus for getting information from your heating and send some commands to it. And you have detached from it some kind of system for your lights.
Best of breed means, you’re using dedicated (the best suited!) systems for different aspects (in our case: heating, light/electric, security, …) - you can always connect the gaps between that systems via openHAB.
My advice is, use one dedicated system for lights and the rest for your electric (outlets, blinds, …) this one saves you much hair, as you only have to adress one system per usecases and not many. You could easily lose track on which device is controlled by which system… If you have e.g. KNX for all your electrical devices - you can stay within the boundaries of KNX and have a basic setup for all actions (switches for light, blinds, …, temparature and motion sensors, …). That way not only the WAF is higher, but you can also use the Basic functions in your house even if openHAB or some other logic modules are offline.