Charts · 26

The visible spectrum is a sliver

My MA, A Journey Through Light, was a cube whose quotes could only be read under ultraviolet light. Nothing in the cube changed when the light did; only what you could perceive. The argument was that what we see is a sliver of what is there. This is the sliver, to scale: the whole electromagnetic spectrum on one axis, the band your eyes respond to drawn at its true width, and what other animals pick up either side of it.

The whole spectrum, to scale

1.6% of this axis is light you can see. It runs from 10 fm to 100 km, 19 powers of ten, and the visible band is the 380 nm to 760 nm sliver in colour.

  • Gamma shorter than 1 pm
  • X-rays 1 pm to 10 nm
  • UV 10 nm to 400 nm
  • Visible 380 nm to 760 nm
  • Infrared 760 nm to 1 mm
  • Microwave 1 mm to 1 m
  • Radio longer than 1 m

Band edges are conventions, not physics: X-rays and gamma rays overlap and are told apart by where they come from, and the microwave and radio boundaries differ between standards. Gamma rays carry on past the left edge: the most energetic photons yet recorded are around 10⁻²¹ m.

Closer, and who sees what

Light, 250 nm to 1 µm: eyes

Heat, 1 to 30 µm: a different sense

Tap a row

Each bar is the range a species’ eyes or sense organs respond to, from the source in the panel. Ticks inside a bar are the peak sensitivities of its receptor types. Bars with a soft edge are ranges the sources give only roughly; the hatched bar is a heat sense, not an eye.

MA cube: UV-A, 315 to 400 nm (ISO 21348), the band a blacklight emits. It is where the quotes in my MA cube, painted in ultraviolet-reactive ink, became readable: the paint absorbs it and re-emits visible light.

37 °C: A body at 37 °C radiates most strongly at 9.3 µm (Wien's displacement law, b = 2.898 × 10⁻³ m·K). Skin is a little cooler, so a little longer.

“Less than one ten-trillionth”, checked

“What we see is less than a ten-trillionth of what’s out there,” David Eagleman told a TED audience in 2015. On the log axis above it is 1.6%. Both can be right, because the spectrum has no top: the fraction depends on where you stop counting, and on whether you count in wavelength or in frequency. Counted in frequency, from zero up to a photon of your choosing:

Stop counting at

Visible light, 394 THz wide, is about one part in 860 trillion of the frequencies up to a 1.4 PeV photon, among the most energetic ever detected. Less than one ten-trillionth.

Cao et al. (LHAASO) 2021, Ultrahigh-energy photons up to 1.4 petaelectronvolts from 12 γ-ray Galactic sources, Nature 594:33. In 2026 LHAASO reported photons from Cygnus X-3 at up to about 3.7 PeV (Natl Sci Rev, arXiv:2512.16638), which would make the fraction smaller still.

Notes

Both axes are logarithmic in wavelength, which is how the spectrum is always drawn, because nothing else fits. Band edges are from ISO 21348:2007, Space environment: process for determining solar irradiances: gamma rays 10 fm to 1 pm, X-rays 1 pm to 10 nm, ultraviolet to 400 nm (ISO’s extreme and vacuum ultraviolet cover 10 to 200 nm), visible 380 to 760 nm, infrared 760 nm to 1 mm, with UV-A, B and C and IR-A, B and C as ISO divides them. ISO’s own microwave and radio bands are specific to the Sun, so those follow the engineering convention, microwave 1 mm to 1 m (300 MHz to 300 GHz) and radio beyond; the ITU counts everything below 3,000 GHz as radio. The CIE (S 017:2020) gives no single edge for the visible: 360 to 400 nm at the short end, 760 to 830 nm at the long. The spectral colours in the bar are approximate; a screen cannot show them.

Animals: human cones from Bowmaker and Dartnall (1980), microspectrophotometry of one retina, peaks 420, 534 and 563 nm; without a lens, Griswold and Stark (1992); honeybee peaks after Menzel and Backhaus (1991) as given by Hempel de Ibarra, Vorobyev and Menzel (2014), range after Peitsch et al. (1992) as given by Garcia et al. (2020); birds from Hart and Hunt (2007), Ödeen and Håstad (2013) and Lind et al. (2014); mantis shrimp from Thoen et al. (2014) and Chiou et al. (2008); pit organs from Gracheva et al. (2010), Grace et al. (1999), Goris (2011) and Ebert and Westhoff (2006). Each row’s panel gives its own sources and how firm they are. The pit organ’s wavelength range is the least certain number here: it is a heat sense with no pigment, and the 3 to 15 µm figure comes from a review rather than a measurement I could check.

The fraction: David Eagleman, Can we create new senses for humans?, TED2015. Visible light is 394 THz wide (380 to 760 nm). On a linear frequency scale that is less than one ten-trillionth of everything up to any photon above about 16 TeV; LHAASO’s 1.4 PeV photons are from Cao et al., Nature 594:33 (2021). On the log axis the same band is a little over 1.5% of the width. The number changes with the scale; the sliver does not.