Oddly behaving Oriental Magpie Robins

There is this OMR pair that lives near my home. Throughout the day one sees them flitting here and there, chasing each other, trying to find food or simply trilling for the heck of it. The pair also nests every monsoon and while the nest itself is not in a visible place the sounds emerging from it are quite audible. 

But to get back to this evening: The robins were awake for more than an hour after darkness had fallen and all other birds had vanished for the night. There is a street light that comes on around sunset. These two robins kept hanging around close to this lamp, swooping and diving to catch the insects and flies fluttering around the light. This went on for quite a while. In between all this hunting the pair would call to each other in a very low pitched bass call that sounded like ‘streak’ or ‘chreek’; very different from the louder ‘chuk chirrup’ they use during the day, or the melodious song of the male heard from treetops during the breeding season.
 
This is the first time (or maybe second) I’ve seen these birds make use of night/artificial light so effectively, delaying their sleep time considerably in the process. Of course I'm not at my observation post every evening so cannot be sure how frequently this happens. 


Would be interested in any observations and explanations from birders.