Connection Problem of Night vision IR led for RasPi Camera
It sounds like it is overheating, which at 3W would not surprise me. You need to attach them to some sort of heat sink.



That big copper pad on the back sort of suggests the thing is meant to be either soldered down to a larger PCB or thermal compounded to a heat sink.

Test the pad first though and see what it is connected to. It may be connected to the live side so electrical insulation may be required between device and heat-sink.