The Indoor Generation: Why We Spend So Much Time Indoors, and Why It Matters

Take a moment to think about your average day. You wake up in your home, travel to school or work, spend the day in an office or classroom, return home, eat dinner and relax in front of the television before going to bed.

For many people, this means spending 90% of the day indoors.

From an evolutionary perspective, that's a remarkable change. For hundreds of thousands of years, humans evolved almost entirely outdoors. Our bodies, brains and biological clock developed under the ever-changing rhythm of natural daylight. Yet within just a few generations, we have become an indoor species.

Our homes and workplaces have become more comfortable and efficient, but our biology has not adapted to this new environment. Our need for daylight remains much the same as it has always been.

How did we become an indoor generation?

Our ancestors spent most of their lives outside. They hunted, gathered food, farmed and travelled under the open sky. Their days were governed by sunrise and sunset, exposing them to bright daylight during waking hours and darkness at night.

Today, life is very different. Many of us work behind a desk, study in classrooms, commute by car and spend our evenings watching television or using digital devices. Technology has allowed us to work, communicate and entertain ourselves without ever going outside. Ironically, the more advanced our society has become, the less natural daylight many of us experience.

Indoor light is much dimmer than daylight

One of the biggest misconceptions about lighting is that indoor enviroenments are bright enough.  For vision, they usually are. For your biological clock,they are often not.

A well-lit office typically provides around 300 to 500 lux on the desk. The amount of light actually reaching your eyes is often lower, particularly if the lighting is indirect or you are sitting away from a window.

Now compare that with daylight:

• A cloudy day outdoors can easily provide 10,000 lux.

• A sunny day often exceeds 100,000 lux.

• Even sitting near a window can expose you to several times more light than sitting deeper inside the same room.

The difference is enormous. Our biological clock evolved under daylight conditions that are often 20 to 200 times brighter than what many people experience during the day.

Why this matters for your body

Your biological clock relies on strong daytime light to know when it's daytime.

When the light during the day indoors is too dim, the brain receives a weaker or no signal. As a result, the distinction between day and night for your body becomes less clear. This can affect many aspects of health, such as your sleep quality, daytime alertness, mood and energy levels.

Your biological clock starts running behind the time of day.

We make evenings too bright

The problem doesn't stop there. While our days are often too dim, our evenings have become much brighter than they were throughout most of human history.

LED lighting, televisions, smartphones and tablets allow us to continue exposing our eyes to biologically active light long after sunset.

This creates exactly the opposite pattern from what nature intended, days that are too dim and nights that are too bright. For our biological clock, this weak contrast can make it harder to know when to be alert and when to prepare for sleep.

We weren't designed for indoor daylight

Our visual system and biological clock evolved under a highly dynamic lighting environment. Every day, nature provided bright mornings, extremely bright midday light, gradually dimmer afternoons, warm sunsets and dark nights.

Indoors, many people experience almost the opposite: similar light levels all day and very little variation in intensity or spectrum.

Our eyes, and especially the spheres (ipRGCs) in the retinae of our eyes, which regulate the biological clock, expect a much stronger daily rhythm than most indoor environments provide.

Getting outside doesn't mean spending hours outdoors

The good news is that you don't have to spend your entire day outside to make a meaningful difference. Small habits can significantly increase your daily light exposure. Follow our Six Steps to Good Light here.

These six steps help strengthen your circadian rhythm and reinforce the natural distinction between day and night.