Physics › Spectrum

Electromagnetic spectrum

Light is a wave. Slow it down and it's a radio signal. Speed it up and it's a gamma ray. Visible light is just a sliver in the middle.

Tune the spectrum

From radio at the left to gamma at the right.

RadioµwaveIRVisibleUVX-rayγ

Band

Visible

The thin slice your eyes evolved to detect.

Frequency

1584.89 GHz

cycles per second

Wavelength

189.29 µm

crest-to-crest distance

One thing in different costumes

Radio, microwave, infrared, visible, ultraviolet, X-ray and gamma — they're all the same kind of wave, just at different frequencies. They all travel at c, the speed of light: 299,792,458 m/s.

Why visible light is <1% of the spectrum

Your eyes evolved to see the slice the Sun pumps out most strongly, and that the atmosphere doesn't block. Bees see further into UV. Snakes see infrared.

Energy goes up with frequency

Radio — low energy, harmless, passes through walls.
Microwave — heats water molecules.
Infrared — heat you can feel.
Visible — what your eye and the camera detect.
UV — enough energy to break some bonds (sunburn).
X-ray — passes through soft tissue, stops at bone.
Gamma — the highest-energy photons we know.

The c = f λ trick

Multiply frequency by wavelength — you always get c. Tune one up, the other goes down. That's why high-frequency waves are short and low-frequency waves are long.