Photon

Why does light slow down as it gets fainter?

Imagine you're walking through a foggy forest at dusk. The farther you walk, the harder it is to see the path ahead.

As light travels through the fog, it spreads out and becomes less intense. This spreading out means each photon carries less energy as it moves further.

Example

A bright flashlight beam (high energy) is clear and focused, but a dim flashlight beam (low energy) spreads out and becomes less visible.

Remember this

The energy of a photon decreases as its wavelength increases, making it less intense and harder to see.

Text adapted from Wikipedia, licensed under CC BY-SA 4.0.

Related concepts

Planck's law

Did you know light behaves differently at tiny scales?

Einstein's photoelectric explanation used Planck's E=hf to predict that higher frequency light ejects faster electrons

Why can't you just turn up the brightness to get electrons flying?

Speed of light

Does moving faster change how fast light travels?

Planck constant

Did you know light and energy are linked by a tiny constant?

Doppler effect

Why does a siren's pitch change as it moves past you?

Einstein's mass-energy paper was only three pages

How can light speed remain constant even when moving?

Swipe through more Physics concepts

Open Pocket Polymath