Light is colour, space and time.
Each particle has colour. Blue ones have much energy, red ones less.
Each light particle moves with the speed of light. Always. With respect to everything.
So light measures space and time with the same unit.
To the Moon: 1.3 seconds. Sun: 499 seconds. Alpha Centauri: 1534 days.
Light is colour, space and time.
Good. What next?
That depends on where you place it.
