The National Library is one of Canberra's most recognisable buildings, thanks in no small part to its stained-glass windows which are a kaleidoscope of colour.

Crafted by artist Leonard French, the 16 windows feature blocks of glass embedded in concrete, cut to maximise light refraction.

And the result is a series of dazzling patterns that flood the library's ground-floor cafe and bookshop.

Incorporating more than 50 colours, the windows of Belgian and French glass feature motifs of crosses, circles, suns, stars and mandalas.

"Early mornings in Canberra are pretty special," said Professor Richard Whiteley from the ANU Art School.

"The way the light is filtered inside because of the lake and the natural environment gives it a great ambience."

The National Library of Australia was opened on August 15, 1968 by prime minister John Gorton. ( ABC News: Penny McLintock )

The library's design was inspired by architect Walter Bunning's visit to the Parthenon in Greece.

Professor Whiteley said the stained-glass windows celebrated the relationship between architecture and artist.

"There's a unique vision of the architect, and the artist can complement that and still have their own voice."

The windows were also designed to reduce the amount of light entering what was the main foyer. ( ABC Canberra: Michael Black )

From painter to glass artist

French's glass windows were installed in 1967, prior to the development of the library's bookshop and cafe, which now feature six pairs and four single-glass windows.

Born in Melbourne, French was originally a sign writer then painter before be became widely admired as a glass artist.

While working on the windows for the National Library, he was also producing a stained-glass ceiling for the great hall at the National Gallery of Victoria.

"The technique that he used was called dalle de verre, which looks very similar to stained glass but it's actually quite different," Professor Whiteley said.

"It seems to be that French was self taught in the technique."

The dalle de varre process involves working with glass that is about 2.5 to three centimetres thick.

"He used a hammer to chip the coloured pieces of glass into the shapes before pouring cement over the top," Professor Whiteley said.

"It's quite different to the delicate work, by comparison, of working with [traditional] stained glass."

A projected image of the stained-glass designs were incorporated into Canberra's annual Enlighten Festival. ( Supplied: National Library of Australia )

Much of the labour involved in production was done from French's studio at Heathcote in central Victoria.

And while the techniques of crafting traditional stained-glass windows date back to the ninth and 10th centuries, Professor Whiteley said dalle de varre glass didn't appear until the 1930s.

"Each piece of glass needed to be chipped by hand and arranged," he said.

"All of the techniques were handmade glass processes.

"It literally means slabs of glass are set in concrete or mosaic material."

In the morning, the sun glows warmly through the glass and creates a magical display inside. ( ABC Canberra: Michael Black )

Dr Grace Blakeley-Carroll, a curator at the library, said the windows delivered a unique ambience.

"The windows have celestial symbols, particularly suns and comets," she said.

"You can also see some of the symbols that Leonard French used in some of his paintings.

"He was particularly interested in turtles and mandalas.

"The more I look at them, I'm always finding new elements."

The National Library of Australia is celebrating 50 years since it first opened to the public.