LED pergola lights very dim all of a sudden

longwalks1

we have a set of pergola lights (about 20 on a string) that weve had for a couple of years with very little use.  previously, when witched on would fully illuminate the bottom of the garden seating area.
Turned them on last night and they did illuminate, but nowhere near enough to light the seating area like before. 
What would cause this please?  trying to get my head around it.  Previously, it was light enough out there to rear a paper at night, now, its still pitch black, but you can just about see the LED filaments in them lit

FreeBear

Corrosion on the contacts or wiring ?

casper_gutman

Are they driven directly from the mains, or in some other way? If they're battery powered, perhaps with a small solar cell to charge them up again, then the battery may have deteriorated to the point where it isn't providing enough oomph for the lights.