Strange lights

While making a cup of coffee I noticed a mysterious flashing outside. So I went to investigate. Five soggy minutes later I am none the wiser. Somewhere in a garden across the block was a source of light, bright enough to light up the whole of the building. It flashed erratically for a while, then flickered with such regularity that it became almost constant and eventually died. I couldn't get a good enough vantage point to see what it was but it was definitely outside and there was no sound other than the rain. It's just one of Those Mysteries.