This is the 4062nd most frequent Japanese word.
ピカ
"ピカ" means "sparkle" or "flash," often describing something bright or shiny.
In this sentence, ピカ (pika) is being used as an onomatopoeia to describe the quick, intense flash associated with a lightning strike. It conveys the brightness and suddenness of the flash.
空が暗くなった瞬間、ピカッと雷の閃光が光りました。
At the moment the sky turned dark, the lightning's flash shined brilliantly.
Here, ピカ (pika) metaphorically represents a sudden flash, used figuratively to describe a moment of insight or realization.
彼のアイデアがとても新鮮で、頭にピカッとひらめいた感じでした。
His idea was very novel, and it felt like a sudden spark of insight in my mind.
In this usage, ピカピカ (pikapika) is a repetitive form of ピカ (pika), used to describe the state of being shiny or sparkling, often associated with cleanliness or newness.