Good Light Guide
Good light is the right light at the right time tailored to our activities and personal needs,
every day of our life. Good light is natural light, or electric lighting indoors that mimics
the beneficial properties of natural light as much as possible.
The wrong light at the wrong time may result in problems such as mood disturbances,
sleep problems, difficulties with learning and memory, problems with vision on the short
term, and health problems on the long term.
Good light is:
The recommendations are intended to be used by healthy people with a day-active schedule. It is not meant as a treatment for patients; people with eye- or skin diseases or who suffer from mood disorders are advised to seek medical advice. This information is not intended for people who work shifts. Working in early shifts, late shifts, night shifts, forward or backward rotating shifts impacts your circadian rhythm. Light interventions to support shift workers need to be personalised and may depend on individual differences, shift work schedules and job demands.
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Natural daylight is the best light
Being outdoor during the day is very important for people. Daytime light intensities outdoor are always higher than indoor, by a factor of anywhere between x10 and x500. And the high light levels outdoor are full spectrum. Sunshine includes infrared (IR) which warms us, and ultraviolet (UV) which when it reaches the skin, supports Vitamin D production, important for calcium uptake for healthy bone structure, and the immune system. The high light intensities we get when outdoor during the day are also important for wellbeing, mood, performance, how we sleep at night and for reducing our sensitivity to light in the evening. Exposure to full spectrum, high intensity daylight
in the morning prevents our biological clock from getting out of sync with the natural 24h light-dark cycle. It prevents our body from running late, and from fragmented sleep, waking frequently at night. The Good Light Group advises people to enjoy natural daylight as much as possible by being outside during the day. Because we are not able to be outdoors all day, every day, the Good Light Group has come with the following recommendations:
Unless you would like to fall asleep and wake up later, take measures to get a dose of natural daylight in the morning immediately after waking up for at least 30 minutes, e.g. by taking a walk or bicycle ride outdoors, or walking or biking to work or school. If it is dark when you wake, try to ‘see’ the first half hour of natural daylight after sunrise.
Take a walk at lunchtime spending at least 30 minutes outside in daylight.
Play or exercise outside during the day.
Especially for children, we recommend spending at least two hours outside in daylight every day.
Studies recommend that for periods longer than 20-30 minutes on sunny and/or warm days, you should protect your skin and eyes in an appropriate way against an overdose of UV radiation from the sun. The most common ways to do this is by wearing protective cloths, a cap, sunglasses, by using sunscreen and/or simply moving to the shadow. Wearing a cap reduces the light coming into your eyes by ~50%, wearing sunglasses reduces the light coming into your eyes by 5-95% depending on the type of glasses.
If it is not possible to spend time outdoors, the next best alternative is to spend as much time as you can during the day sitting close to (<1m) and facing a window.
Indoor light for healthy daytime-active people
People worked and lived outside in natural daylight for many thousands of years. Since the industrial revolution this has changed significantly. Today, people spend 90% of their time indoors. That makes having Good Light indoors essential for our health and wellbeing.
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Good light is Attractive
Just like in nature, indoor light should be attractive, comfortable and of high quality. This is achieved when indoor lighting shows colours naturally, does not cause too much glare, does not have unwanted artifacts or flicker, provides attractive contrast, lights the space comfortably, does not make noise and feels safe.
Design tips to implement attractive light indoors:
Let daylight in as much as you can through windows and skylights.
Increase the overall brightness of the room, don’t only light the work surface or task but light the surroundings e.g. the walls and the ceiling.
Use accents of light to create attractive contrast.
When you select lighting, choose for a Colour Rendering Index (CRI or Ra) of at least 80.
Avoid Discomfort Glare: design for a Unified Glare Rating (UGR) of 19 or less in longstay areas (≥30 min) and for UGR ≤ 22 in short-stay areas (<30 min).
Avoid Temporal Light Artefacts: Flicker Pst ≤1.0 and Stroboscopic effects: Stroboscopic Visibility Measure (SVM) ≤1.0.
Limit audible noise from the lighting installation to ≤24 dBA at 1m distance.
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Good light is Dynamic
The amount of daylight we are exposed to outdoors varies during the day both because
daylight itself is ever changing and because we are moving around ourselves, changing
what we look at and see, and making changes to the space we are in like sitting in
the shade. It might be advantageous to mimic these changes to some extent indoors.
People need high light levels during the day, and low light levels during the evening
before going to sleep. Good Light indoors is stimulating during daytime with an intensity
that preferably exceeds the traditional standards for indoor lighting by a factor 5, while
during the evening the preferable light level is dimmed by a factor 5, provided it remains
comfortable and safe.
For people 45-50 years and older, higher light intensities and probably spectral changes
may be needed to support visual and non-visual (biological and emotional) needs.
This is largely due to the normal degrading processes happening in the eye. Many people
recognize this as the time when they start needing reading glasses.
Design tips to implement attractive light indoors:
Use a lighting system that enables you to change the light level; dimming =reducing the light level and/or boosting =increasing the light level.
Use lighting systems that enable you to change the distribution of light in the room during the day, effectively mimicking daylight.
Provide horizontal and vertical light levels that ensure adequate visual performance and comfort, while simultaneously providing non-visual (biological and emotional) benefits.
In the next table you will find our recommendations for horizontal light levels. These levels are based on a combination of best practices and scientific arguments.
Please note that these light levels must remain comfortable and adequate for the age
of the user and the specific task. Timing should be personalised so that it supports
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Good light is Optimized
Just like in nature, the spectral properties (colours) of ideal indoor light vary as a function of the time of day. Light spectrum can be optimized to meet personal needs and preferences and to support specific tasks. During the day, the light spectrum should include a reasonable portion of short wavelengths (cyan light colour) to provide the energizing and revitalizing benefits of light. In the evening and at night, the amount of short wavelengths should be minimized to support winding down, enabling a good night’s sleep and preventing disruption of the day-night rhythm. With age, from 45-50 years and older, the spectral characteristics required for optimal functioning may change because of changes in the eye, e.g. in the case of the development of cataract.
Design tips to implement optimized light indoors:
Use lighting systems that are ‘tuned’ or ‘tuneable’ to support a specific activity. A lighting system is ‘tuned’ if the spectrum is selected to support a specific activity at a specific time of the day. A lighting system is considered ‘tuneable’ if the light spectrum can be changed. ‘Tuneable white’ systems are most common and can vary in Correlated Colour Temperature (CCT). Please note that CCT is only a proxy for spectral content: two light sources with the same CCT can have totally different spectra and therefore a totally different impact on the human non-visual system. The real spectrum is more important than a CCT number. For this reason, you may also choose to use a more advanced ‘tuneable colour’ system. These systems vary not only in CCT, but also in spectral content and in colour.
Although not very common yet, some have reported that it may be beneficial to use a lighting system with additional spectral benefits which can be found in the non-visual part of the spectrum, e.g. supporting Vitamin D production or photobiomodulation.
Design not only for horizontal light levels as suggested in most lighting application standards, but also for light on the eye. During most daytime activities, this is the vertical light level at sitting or standing height.
The recommended levels in the table below are partly based on recent recommendations of a group of scientists, and age corrections, and partly based on our own interpretation thereof.
*Melanopic equivalent daylight illuminance (in the table abbreviated to MEDI) is one of the metrics defined in the international Standard CIE S026:218 recommended to be used in measuring the non-visual effects of light
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Good light is Personal
Good Light indoors can be adapted by the user for personal needs based on suggestions by the system. Individuals may differ in light appreciation with respect to intensities and preference for warm or cool tones of (white) light. In addition, individuals can differ in the timing of their sleep-wake phase, also referred to as being a different chronotype. Early chronotypes have a morning preference and late chronotypes an evening preference. This results in individual needs when it comes to the timing of the dynamic 24h pattern of light, and both its intensity and spectral characteristics. In addition, having personal control over the dynamics and spectral characteristics of light is highly appreciated by individuals.
Design tips to implement personal light indoors:
Consider using a lighting system with a pre-programmed pattern over the day, and that provides the proper light intensity and spectrum at the proper time.
Consider using a lighting system that offers pre-programmed, task specific light settings to support a range of different activities.
Many individual users appreciate having personal control over the dynamics and spectral characteristics of the light. The amount of control, or adaption ranges can be selected by the system and made time of day dependent.
Consider using more advanced lighting systems which include environmental sensors beyond those applied to measure and control the lights. Incorporating sensors like temperature, noise detection, air quality can serve to safeguard and support health and wellbeing of the users. This type of Indoor Environmental Quality sensors should be connected to other building automation systems.