speed of light
Refers to the physical constant or the concept of light's speed. Often used in scientific contexts or metaphorically to indicate extreme speed.
The speed of light is about 300,000 kilometers per second.
The information spread around the world at the speed of light.
Compound of 光 (ひかり, 'light') + の (possessive particle) + 速さ (はやさ, 'speed'). A straightforward descriptive phrase.