Italian Renaissance painter Caravaggio used revolutionary optical instruments to "photograph" his models more than 200 years before the invention of the camera, according to a researcher in Florence.

The 16th century artist celebrated for his dramatic chiaroscuro (light and shadow) paintings mastered "a whole set of techniques that are the basis of photography", Roberta Lapucci told AFP.

Caravaggio worked in a "darkroom" and illuminated his models through a hole in the ceiling, said Prof. Lapucci, who teaches at the prestigious Studio Art Centres International in the Tuscan capital.

The image was then projected on a canvas using a lens and a mirror, she said.

Caravaggio "fixed" the image, using light-sensitive substances, for around half an hour during which he used white lead mixed with chemicals and minerals that were visible in the dark to paint the image with broad strokes, Prof. Lapucci said.

She has hypothesised that Caravaggio used a photoluminescent powder from crushed fireflies, which was used at the time to create special effects in theatre productions.

One of the main elements of these mixtures was mercury - to which prolonged exposure can affect the central nervous system causing irritability and other symptoms - which Prof. Lapucci said would help explain Caravaggio's notorious temper. Caravaggio used a photoluminescent powder from crushed fireflies.

One of his many brawls ended in the death in 1606 of a young adversary, Ranuccio Tomassoni, which forced him to flee Rome to Malta.

"The entire set-up was suggested to him by his friend Giovanni Battista Della Porta, a physicist," Prof. Lapucci said. "Caravaggio was very tied to a community of scholars interested in optics."

While Leonardo da Vinci (1452-1519) had earlier described the camera obscura or darkroom, Caravaggio was the first painter to use it, Prof. Lapucci said.

The Italian researcher has collaborated with British artist David Hockney, who wrote in his 2001 book Secret Knowledge that Caravaggio and later the Flemish Baroque artist Anthony Van Dyck (1599-1641) and French neoclassical painter Jean Auguste Dominique Ingres (1780-1867) used optical instruments to compose their paintings.