Light can have a strong effect on people -- about 5 percent of the world's population is reckoned to suffer from a form of depression called seasonal affective disorder (SAD), which has been linked to sunlight deprivation.

Light also affects us in lots of smaller, subtler ways, according to Ingo Maurer, a world-renowned lighting designer, whose designs are often presented as works of art in galleries and museums. Right now, a four-decade overview of his career, "Light -- Reaching for the Moon," featuring rare prototypes, serially produced lamps and one-off pieces, is showing at the Tokyo Opera City Art Gallery till Sept. 18.

"We need air and we need light," he says as we sit down to discuss the exhibition. "Light is a fundamental thing like bread. We need it to hold us up. It miraculously keeps us going. It's not only natural light, but artificial light too."

Maurer notices the rather garish fluorescent-tube lighting of the conference room we have commandeered for the interview, and says wistfully, "In this room we have dead light -- it drains you of emotion."

Despite this, the sprightly 74-year-old German is animated and full of passion as he talks about a career that started in the 1960s.

In those days of simple incandescent lighting, his focus was on designing light-delivery systems, rather than "designing the light" itself. His first successful design, "Bulb" (1966), was an eye-catching table lamp, which expanded the motif of the bulb to the whole lamp, creating a giant freestanding light bulb.

"I was lying in a cheap pensione in Venice," he says, recalling the moment of inspiration. "I had eaten and drunk well and I was high. The crickets were chirping. I had drunk a nice Tokai, then I was struck by the light bulb hanging from the ceiling. It seemed to look much larger than normal." The success associated with this design -- it was later acquired by MOMA for its collection -- allowed him to get an independent design firm off the ground.

Subsequent improvements in lighting technology, including the widespread introduction of halogen lighting and light-emitting diodes (LED), helped him to expand his focus beyond the aesthetic and formal characteristics of the devices to the quality of the light emitted. It was an area he was already exploring through various techniques that reflected, refracted and softened the harshness of direct light.

One of the most interesting pieces from these experiments is "Porca Misseria!" (1994), which uses shards of broken porcelain clustered round a bright halogen light source to create an explosive and dynamic work that filters out the harshness of the light. Even more spectacular is a more recent version, "L'Eclat Joyeus" (2005), that incorporates fragments of porcelain statuettes of Chinese gods.

His softer side is visible in "Tableaux Chinois" (1989), which sets floating mirrors on a fish pond and projects the beautiful patterns created by the interaction of light and water onto a wall. The work is mesmerizing, and achieves one of Maurer's cherished goals of making light itself visible and "giving it substance."

"Originally I did this work for the Foundation Cartier," he says. "I had the idea of making something moving, using mirrors. I called it 'Tableaux Chinois' because it reminded me of a Chinese ink-painting. Each moment is a new work."

Japanese art has been an important influence on Maurer. Inspired by the round, paper akari lanterns created by Japanese-American sculptor Isamu Noguchi, he has fashioned several highly artistic designs handmade from paper using Japanese techniques. The series is called "MaMo Nouchies," a pun on Noguchi's name, and includes the elegant "Wo-Tum-Bu" (1998), which are equally at home in modernist interiors or traditional Japanese tatami-mat rooms.

"I like the light they produce," he enthuses. "That's why I decided to make lamps using Japanese paper. People called up and said, 'Our conferences have become much more inspired, thanks to your light.' So it definitely works."

Since the 1990s, Maurer has been involved in a number of large-scale architectural-style projects, such as the lighting for the Westfriedhof Subway Station in Munich, and a current project renovating Brussels' most famous landmark, the Atomium, which was originally built for the 1958 International Exhibition. Rather than sheer creativity, this kind of work requires teamwork and involved consultation with clients. Maurer sees this as the price he has had to pay to keep his operational independence.

"I have to pay my bills," he says. "I have 60 to 70 people working for me. But I try to make as few compromises as possible. If there is some kind of terrible stinker, I won't do it."

On the Westfriedhof Subway Station project in 1998, the client insisted on using fluorescent tubes, a garish lighting he dislikes.

"Why do people try to improve on natural light?" he laments, referring to the flickering, partial-spectrum light created by those tubes. Faced with this problem, he skillfully ameliorated the ugly glare by using large aluminum dome caps with brightly painted inner surfaces as light shades, giving the unstable light in each dome a stable and beautiful color.

Perhaps this is the difference between an artist and a designer. The essence of the artist is to crave complete creative freedom, while the designer's main focus is on the practical and utilitarian. The thing that makes Ingo Maurer a great designer as well as a great artist is that he manages to pull off both roles.