It's pretty much essential that your home knows if it is dark or light outside, if you want to control things intelligently. It makes a lot of sense to control security lighting, safety lighting, automated curtains, etc. at the right times. Not only does this make your house look more secure but, it also saves energy.
Twilight sensors are typically bought integrated into outside lighting and other products but, doing this in a centralised fashion enables more much intelligent control.
The weather is an obvious factor in when it gets dark at night and lighter in the morning. For the purposes of control and automation, it makes sense to take account of these external conditions. We have recorded differences between calculated sunset and detected dusk greater than 60 minutes.
Also worth mentioning that when it gets dark, you do not want to close all the curtains at the same time! This does not make your house look occupied and creates a large load spike.
We have completed a project to implement our twilight sensor.