Light is electromagnetic radiation — and behaves both as waves and particles (photons).
Quick check
Light from a distant star takes years to reach us. Roughly how fast does it travel through space?
Photon energy & wave relation
Light is both a wave (frequency f, wavelength λ) and a stream of photons each carrying energy h·f. Higher frequency (bluer / UV) ⇒ more energetic photons.
The visible slice
- Roughly 400–700 nm — a tiny window of the full electromagnetic spectrum.
- Just below 400 nm: ultraviolet (sunburn).
- Just above 700 nm: infrared (heat you feel from a fire).
- Red is the longest visible wavelength, violet the shortest.
Because light has a finite speed, looking out into space is looking back in time — the Sun you see is 8 minutes old, and some galaxies you see as they were billions of years ago.
Visible light is roughly 400-700 nm. Below: UV. Above: infrared.