THE ELECTROMAGNETIC SPECTRUM

eighteen decades of frequency · and how much of it the eye sees

Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.

Three sizes in one archive — from a sheet on the fridge to a poster on the wall.

Formats: A4 · A3 · A2
What you get: Print-ready PDFs, one per size, with every letterform converted to outlines — nothing to install, nothing to shift.
Subject: science · everyone · comparison · study

Every wavelength here is computed from the frequency: λ = c / f, with c = 299,792,458 m/s exactly, by the SI definition. Radio bands follow ITU-R V.431, optical limits ISO 21348. X-rays and gamma rays are told apart by origin rather than by wavelength, so no boundary between them is drawn.

THE EYE SEES ONE OCTAVE, THE EAR HEARS TEN

Visible light by the ISO 21348 limits runs from 380 to 760 nm — exactly a factor of two, which is one octave. The audible range from 20 Hz to 20 kHz is 9.97 octaves — very nearly ten.

So hearing covers ten times the span that sight does, and that is why music has octaves and colour does not: double the frequency of red and you leave the visible range rather than arriving at "the same colour, higher".

The limits of the visible are not a property of the eye but a convention: another standard takes 400–700 nm, and then it is no longer a clean octave. That is why the sheet says whose limits it counted by.

On the sheet

Every wavelength here is computed from the frequency: λ = c / f, with c = 299,792,458 m/s exactly, by the SI definition. Radio bands follow ITU-R V.431, optical limits ISO 21348. X-rays and gamma rays are told apart by origin rather than by wavelength, so no boundary between them is drawn.
Colour carries meaning, but meaning never rests on colour alone — the sheet reads in black and white.
Nothing about how it was made: the sheet carries only what the reader needs.

Printing

Three sizes in the archive: A4 — 210×297 mm, A3 — 297×420 mm, A2 — 420×594 mm.
All text is converted to outlines. No fonts to install, and nothing shifts on another machine.
White background and sparing fills — it prints on a home printer without draining the cartridge.
Margins of at least 10 mm: a home printer cannot print to the edge.
No stroke thinner than 0.3 mm, so nothing disappears in print.

Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 7 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.

THE ELECTROMAGNETIC SPECTRUM

THE EYE SEES ONE OCTAVE, THE EAR HEARS TEN

On the sheet

Printing

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