you and two friends, Al and Be, are outside at night time. Al has a flashlight and flashes it at you and Be. Be is 20 feet away from Al, and you're 20 feet behind Be.
20ft 20ft
Al..........Be...........you
r1 r2
The photons from the light Al has hits Be first, so he sees it first. it took .03 seconds(r1) to reach Be.
After that, the photons hit you and you can see it. it took .03 seconds(r2) to reach you from Be.
They were both .03 seconds because you are equally apart and the speed of light is finite.
so, how long did it take the light to reach you from AI?