Your work gives me a feeling of joy,” one of the professors said. The others nodded. I should have been happy. Nine months before, I had left my career as a brand strategist to pursue a graduate degree in a field in which I had no experience: industrial design. Many times over the course of the year I had felt overwhelmed by the new skills I needed to learn, from drawing to colour-mixing to woodworking. But today I had passed the assessment, and I did feel relieved to know that my career shift hadn’t been a giant mistake.

And yet, as I looked at those nodding faces, my heart sank in my chest. I wanted to be a designer because I believed design could solve serious problems. I volunteered with a non-profit organisation designing low-cost reflective backpacks to prevent roadside injury among schoolchildren in Ghana. Late at night, I pored over books on renewable materials and environmentally friendly manufacturing strategies. I had hoped the professors would see in my work a commitment to using design to build a safer, fairer, more sustainable world. Instead, they saw joy.

Joy seemed light and fluffy. It was nice, but definitely not serious or substantial. I wondered if that was how they saw me: a nice young designer who made things that made people smile. Not things that could change the world.

Still, though I was disappointed, something about the professor’s comment caught my attention. Joy was a feeling: ephemeral and elusive. It wasn’t something we could see or touch. How, then, could the collection of simple objects I had presented – a cup, a lamp, a stool – elicit joy? I tried to get the professors to explain, but they hummed and hawed as they gestured with their hands. “They just do,” they said. I thanked them, but as I packed up my things for the summer, I couldn’t stop thinking about this question.

How do tangible things create this intangible feeling of joy? At first, the answer seemed unequivocal: they don’t. Sure, there’s a certain pleasure in material things, but I’d always been led to believe that this is superficial and short-lived, not a meaningful source of joy. In all the books on happiness I’d consulted over the years, no one had ever suggested joy might be hiding inside my closet or kitchen cabinets. Instead, countless experts agree that the kind of joy that matters is not around us but in us. This perspective has roots in ancient philosophical traditions. The teachings of Buddha advise that happiness comes only from letting go of our attachments to worldly things. The Stoic philosophers of ancient Greece offer a similar prescription, rooted in self-denial and rigorous control over one’s thoughts. Modern psychology, likewise, embraces this inward lens, suggesting the way to a happy life is to change how we look at the world and our place in it. From mantras and meditation to therapy and habit change, true joy is an exercise of mind over matter, not matter over mind.

Yet in the weeks and months that followed my review, I noticed many moments when people seemed to find real joy in the material world. Gazing at a painting in an art museum or making a sandcastle at the beach, people smiled and laughed, lost in the moment. They smiled, too, at the peachy light of the sunset and at the shaggy dog with the yellow galoshes. And not only did people seem to find joy in the world around them, but many also put a lot of effort into making their immediate environment more delightful. They tended rose gardens, put candles on birthday cakes and hung lights for the holidays. Why would people do these things if they had no real effect on their happiness?

‘An increase in sunlight in a workspace has been linked to better sleep and increased physical activity among office workers’. Illustration: Francesco Ciccolella

I needed to know exactly how the physical world influences our emotions and why certain things spark a feeling of joy. I began asking everyone I knew, as well as quite a few strangers on the street, to tell me about the objects or places they associated with joy. Some things were specific and personal, but many examples I heard over and over again. Everywhere, it seems, rainbows are joyful. So are beach balls and fireworks, swimming pools and treehouses, hot-air balloons and ice-cream sundaes with colourful sprinkles. These pleasures cut across lines of age, gender, and ethnicity. They weren’t joyful for just a few people. They were joyful for nearly everyone.

I gathered pictures of these things and pinned them up on my studio wall. Each day I spent a few minutes adding new images, sorting them into categories and looking for patterns. Then one day, something clicked. I saw lollipops, pom-poms and polka dots, and it dawned on me: they were all round in shape. Vibrant quilts kept company with Matisse paintings and rainbow candies: all bursting with saturated colour. A picture of a cathedral’s rose window puzzled me at first, but when I placed it next to a snowflake and a sunflower, it made sense: all had radiating symmetries. And the common thread among bubbles, balloons and hummingbirds also became clear: they were all things that floated gently in the air. Seeing it all laid out, I realised that though the feeling of joy is mysterious and ephemeral, we can access it through tangible, physical attributes. Specifically, it is what designers call aesthetics – the properties that define the way an object looks and feels – that gives rise to the feeling of joy.

Up until this point, I had always thought of aesthetics as decorative, even a bit frivolous. This attitude is common in our culture. Though we pay a fair amount of attention to aesthetics, we’re not supposed to care too much about them or put too much effort into appearances. If we do, we risk seeming shallow or insubstantial. Yet when I looked at the aesthetics on my studio wall, I realised they were far more than just decorative. They elicited a deep, emotional response.

The summer after my review, I began to see the power of this response firsthand. My grandmother was in the last stages of cancer and, once a week, I took the train out to my mother’s house to visit her. I brought flowers – tulips, snapdragons or sweet peas – whatever looked freshest at the florist. As I walked into the room, I’d see her face light up. I’d take the vase and change the water, tossing the dead stems into the bin and mixing the ones that still had life in them with the new blooms. I fluffed and separated them, and set them on the table next to the bed. Nana’s gaze drifted from me to the flowers and back again as we chatted. Even as she grew more remote, her eyes clouded and hands brittle, she always smiled at flowers. And when at the end of each visit I had to leave to catch my train home, I would peer back as I was shutting the door to see her, small and pale in my childhood bed, still gazing at them.

Nana died that summer and, not long after, I began to hear stories of how what I’d started to refer to as the “aesthetics of joy” were being applied on a much larger scale. In Tirana, Albania, in 2000, newly elected mayor Edi Rama decided to cover the buildings at the heart of the city with vibrant swathes of orange, turquoise, red and yellow. Albania was the poorest country in Europe and Tirana, its capital city, was so depressed that as Rama has said: “The only hope in Tirana was to leave it.”

When Rama, an artist and former basketball star, took office, he found the city’s treasury empty, depleted by years of citizens refusing to pay their municipal taxes. He used money set aside by the EU for historic preservation to fund the painted buildings, using designs he sketched himself. Many residents were outraged to find their shops or apartments painted in gaudy hues without their knowledge or consent. But soon new shops began to open, and the ones that were already there began to take the heavy metal grates off their storefront windows. They claimed the streets felt safer, even though there had been no increase in the police force. The number of businesses tripled, and the tax revenues increased by a factor of six. This revenue enabled Rama to refurbish green spaces, plant trees and restore public services. By the end of Rama’s time in office, Tirana had become not just a viable place to live, but an international tourist destination.

How could something as seemingly superficial as colour have such a profound effect? I discovered a possible answer in a cross-cultural study of colour in workplace environments, which revealed that people working in more colourful offices were more alert, friendly, confident, and joyful than those working in drab spaces. Bright colour makes our surroundings feel alive, which in turn energises us and changes how we engage with others. Perhaps this is why the New York-based non-profit Publicolor, which uses vibrant hues to transform neglected schools and community sites, has heard from administrators that student and teacher attendance improves and vandalism declines in its painted schools. Or why Hilary Dalke, a colour specialist who has worked with the NHS, has found that care home residents often ask for the brightest colours to be painted in their bedrooms.

Joy is something we’re meant to grow out of. And this bias runs deep in our society

Over time, I began to find that colour isn’t the only aesthetic of joy that can have a deep influence on our wellbeing. Flowers, for example, have been shown to improve not only mood but also memory in older adults. Researchers have found that being exposed to images of symmetrical, harmonious rooms reduces the likelihood of cheating on a test when compared with looking at images of unbalanced, asymmetrical spaces. Some of these effects have even been traced to specific neurological structures. When neuroscientists show people pictures of angular objects, they find that a part of the brain called the amygdala, associated in part with fear and anxiety, lights up, yet stays quiet when they look at round versions of the same objects. The delight of a balloon, a beach ball, or a curvy Thomas Heatherwick installation is not just a passing pleasure. It reaches deep into our minds, lightening our mood and setting us at ease.

These findings changed the way I see joy, from light and insubstantial, to light and very substantial. Ten years after that review, I look back and wonder how I got the impression that joy wasn’t significant, or why I believed that lightness was incompatible with serious impact. I believe it stems in part from a cultural bias in Western society that equates joyfulness with childishness and a lack of sophistication. Joy is something we’re supposed to grow out of. Adults who are exuberant or silly or who wear bright colours or paint their houses with them aren’t to be taken seriously. This is particularly true for women. We risk looking frivolous when we buy flowers or invest in throw pillows simply because they bring us joy.

This bias runs deep in our history, and is tinged with ethnic prejudice. Two hundred years ago Goethe wrote in his Theory of Colours that “savage nations, uneducated people, and children have a great predilection for vivid colours,” but that “people of refinement avoid vivid colours in their dress and the objects that are about them, and seem inclined to banish them altogether from their presence.” The built environment reinforces this belief. Serious places, such as government buildings and corporate headquarters, are dull rectangles furnished in sombre tones of grey and beige. Only playgrounds and primary schools are allowed to be colourful.

The impulse to seek joy in our surroundings is deeply human. It evolved over thousands of generations to motivate our ancestors to seek out the things in their surroundings that enhanced their likelihood of survival. We find joy in vibrant colours, round shapes, symmetrical patterns and lush textures because these aesthetics indicated to early humans that an environment was nourishing, safe, balanced and abundant. On a fundamental level, the drive towards joy is the drive towards life. Knowing this has allowed me to let go of the judgment I once felt about joy and, instead, recognise that it has an important role to play in a healthy life, and in a healthy society.

The beauty of the aesthetics of joy is that we can use tangible means to address intangible problems. A study of prisons has shown that viewing videos of nature scenes can decrease violence by up to 26%. An increase in sunlight in a workspace has been linked to better sleep and increased physical activity among office workers. A move as simple as changing lightbulbs has been shown to reduce depression and cognitive decline in patients with Alzheimer’s disease. Initiatives that once might have been seen as cosmetic, many of which are low-cost, can have far-reaching consequences. And research on these types of initiatives is still only in its early stages.

At the same time, there’s also the more personal side of the aesthetics of joy: the flowers brought to loved ones in hospital, the polka-dotted scarf saved up for and treasured, the yellow door painted as a gift to the neighbourhood. In my own life, these 10 years of researching the aesthetics of joy have made me far more attuned to the joy in my surroundings. Rather that dismissing these moments as inconsequential to my happiness, I’ve come to see the world as a reservoir of positivity that I can turn to, any time.

Joyful : the Surprising Power of Ordinary Things to Create Extraordinary Happiness by Ingrid Fetell Lee is published by Rider on 6 September at £20. To order it for £17, go to guardianbookshop.com