A single thin white line enters from the left edge, dead straight, and strikes the face of a glass triangle floating in absolute black. What comes out the other side is no longer white. It fans into a clean spectrum of red, orange, yellow, green, blue and violet, the colours stacked in tidy parallel bands that march off toward the right edge of the sleeve. There is no band photo, no title, no name, nothing but this one quiet act of physics happening in the dark. That emptiness is the boldest choice on the cover.
The prism itself is rendered in cool blue-grey, its three edges catching faint highlights so it reads as solid, weighty glass rather than a flat shape. You can see the white beam refract inside it, bending as it crosses the interior before exiting as colour. The eye lands first on that bright entry line, follows it into the triangle, then is released outward along the rainbow. It is a tiny piece of theatre, and it works because everything around it is pitch black.
The brief behind it was almost comically modest. Keyboardist Richard Wright asked for something simple and bold, not another photograph. He wanted it 'smarter, neater, more classy,' something with the restraint of a Black Magic chocolate box. The job went to Hipgnosis, the studio of Storm Thorgerson and Aubrey Powell, who until then had made largely photographic sleeves for the band, the kind of wordless designs that had left EMI confused.
Thorgerson answered Wright's request by reaching for a science book. The prism dispersing white light came from a photograph he found in a 1963 physics textbook, and an Alex Steinweiss illustration made for the New York Philharmonic's 1942 performance of Beethoven's Emperor Concerto fed into the idea too. Thorgerson said the triangle pointed mostly at the band's live light shows, but also worked as a symbol of thought and ambition, a fit for Roger Waters' lyrics. The final crisp line drawing was made by Hipgnosis associate George Hardie, who slightly rearranged the textbook image and specified every colour as percentages of magenta, cyan, yellow and black straight off a printer's chart. The rainbow you see was effectively dialled in by numbers.
What makes the story better is that this was not the only option. Hipgnosis laid out seven different designs for the band to choose from. All four members pointed at the same one. Waters remembered it simply: 'We all pointed to the prism and said "That's the one."' It was Waters too who suggested the spectrum keep going, extending across the gatefold to meet a heartbeat blip, so the colours pulse on into the fold like a pulse on a monitor.
The album arrived in March 1973, out in the US on 1 March and the UK on 16 March, on Harvest in Britain and Europe and Capitol in the States. The music inside became one of the best-selling records ever made, certified 14 times platinum in the UK and topping the Billboard chart in America. But the front of the sleeve had a life of its own.
Given near-total creative freedom, Hipgnosis made an image with no words on it at all and watched it become shorthand for the band themselves. The prism has since been printed on countless T-shirts, posters and bits of merchandise, recognised by people who have never heard a note of The Dark Side of the Moon. A diagram from a physics book, redrawn by hand and floated in the dark, turned into one of the most reproduced pictures in popular music.
