Can somebody tell me, what is that component and what is its function(see the attached photo)?

 

That is an AC operated LED luminaire. The IC controls the number of LED in a series string to adjust the string voltage to keep the current constant, and ensure a unity power factor.

 

That is an AC operated LED luminaire. The IC controls the number of LED in a series string to adjust the string voltage to keep the current constant, and ensure a unity power factor.

Don't leds need DC instead AC voltage?

 

Don't leds need DC instead AC voltage?

The four lead component marked DB1 is a full wave bridge rectifier which takes the AC and converts it to DC.

 

The LEDs do get a DC voltage because there is a bridge rectifier, full wave, item BR1 , the 4 legged black square towards the top of that PCB. The other two devices are switching controllers. They regulate for a constant current.