How many lux do you actually need?
We often talk about getting “enough light” during the day. But what does enough actually mean? Is the light in your home or office bright enough? Is sitting near a window enough? And does everyone need the same amount of light?
The answer depends on several factors, including the time of day, where the light is measured and, importantly, your age.
First things first: what is lux?
Lux is a measure of how much light falls on a surface. One lux equals one lumen per square metre. When we talk about light for health and your biological clock, however, the amount of light on your desk isn’t necessarily what matters most. Your body responds to the light that reaches your eyes. That is why we recommend measuring light vertically at eye level, facing the direction you normally look.
An office might have 500 lux on a desk, for example, while the amount of light reaching your eyes could be considerably lower.
How much light do you need during the day?
As a practical rule of thumb, younger adults should aim for at least 500 lux at eye level during the day. This might sound like a lot, especially compared with many indoor environments, but it is still relatively dim compared with being outdoors. Even an overcast day outside can provide thousands of lux.
Bright daytime light helps tell your biological clock that it is daytime. This supports the daily rhythm that regulates alertness during the day and prepares the body for sleep at night.
If you can, spend plenty of time outdoors and sit or work close to a window during the day. When there is not enough daylight available, use electric lighting that provides sufficient light at eye level.
As we age, we need more light
Our light requirements change as we get older. As the eye ages, the lens becomes less transparent and the pupil tends to become smaller. As a result, less light reaches the retina. This means an older person may need considerably more light than a younger person to receive a similar amount of light at the eye.
As a practical guideline, older adults should aim for around 1,000 lux at eye level during the day. So while approximately 500 lux may be suitable for a younger person, an older person may benefit from roughly twice that amount.
This becomes particularly important because older adults often spend more time indoors, where light levels can already be much lower than outside.
light indoors is not the same as daylight
Our perception can be misleading. A room can feel perfectly bright while providing relatively little light to the eyes. Typical indoor lighting is much dimmer than natural daylight. While an indoor environment may provide a few hundred lux, outdoor daylight can easily reach several thousand or even tens of thousands of lux.
This is one reason why simply switching on a ceiling light is not always enough.
During the day, make daylight your first choice. Go outside regularly, open the curtains and position yourself close to a window. If daylight is limited, particularly during dark winter months, supplement it with good electric lighting.
More during the day, less in the evening
Getting the right amount of light is not just about brightness. Timing matters too. During the day, your body needs plenty of light. In the evening, it needs the opposite.
A simple daily light rhythm could look like this:
Younger adults during the day: aim for at least 500 lux at eye level
Older adults during the day: aim for around 1,000 lux at eye level
Three hours before bedtime: keep light levels below 10 lux
During the night: keep light levels below 1 lux and avoid screens whenever possible
In other words: bright days and dark nights.
Check your own light levels
Want to know how much light actually reaches your eyes? Measure the light vertically at eye level using a lux meter. You can also use a lux meter app on your phone to get an indication, although smartphone apps are not always accurate and can overestimate light levels. Try measuring in different places: at your desk, next to a window, in the middle of the room and outside. You might be surprised by just how big the differences are.
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