电光

Often paired in the chengyu 电光石火 (diànguāng-shíhuǒ, "electric light and flint sparks") — meaning a fleeting instant, used to describe lightning-fast reactions or fleeting opportunities. In modern technical contexts also covers "electro-optic" / "electric arc."

memory

电 (electric, lightning) + 光 (light) — both natural lightning and man-made electric light. The character 电 itself originally pictured lightning streaking from a cloud.