Nummi began his career in 1950’s straight from the Central School of Industrial Art at the Orno design company. His special material was lamps made from perspex, or acrylic plastic, which was lightweight and refracted light beatifully. He eliminated everything unnecessary or decorative from the lamp, favouring simple geometric shapes such as spheres, cones and cylinders.

Nummi has designed many familiar Finnish lamps such as the Lokki and Kurki. His Modern Art lamp was chosen to the collection of the Museum of Modern Art in New York.

In addition to being an expert of light he was also an expert colourist. From 1970’s Nummi concentrated on colour design and was the head of  the planning department of Tikkurila paint factory. He first developed the Jokeri colour scheme containing 144 colours.

Aalto University Archives hold the private collection of Yki Nummi comprising the exhibited original drawings, colour schemes and an extensive collection of documentation about his life work.