Light via eyes
Light is needed for vision, but light entering eyes also has other non-image forming effects. It is the main Zeitgeber for the biological clock in our brain and it has acute effects on our body and on levels of energy and mood.

Right light at the right time of day
Some of the non-image forming effects of light exposure depend on the colour of light in combination with timing of exposure. Some colours and intensities that are beneficial at one time of day may be detrimental at other times of day.


Light and waking up
In nature, daily life is innitiated by the upcoming Sun, and comes to rest after the Sunset. Modern society respects different daily schedules, we often need to get up before the sunrise, and continue activities till long after the sunset.
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Sleep patterns
In modern society we have the capability to prolong the light part of the day by using artificial lighting. Our bodies are not synchronized to the rhythm of the Sun, but to our lifestyle.
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We need light for vision, but light also plays an important role in regulating our sleep-wake rhythm, how we feel and how well we are able to work with our brain.

To keep the 24-hour rhythms in our body in synch with the natural environment, we need light at particular times of the day and darkness at other times. Light in the morning induces our rhythms to shift to an earlier phase, light in the evening shifts our rhythms to a later phase.

Light exposure through our eyes also has a clear effect on our body:
It is in particular the blue part of the light spectrum that is important for all these "non-image forming" responses.

Light during the day and darkness during the night is supporting a good night of sleep and a day full of energy. Most people recognize they feel much more energetic during a bright, sunny, day and often enjoy a sound sleep afterwards. Dark, gloomy days, especially in winter may induce feelings of lethargy, low spirit and sleepiness.

The reason why some people experience mild changes in energy levels, sleep need, and mood in winter, and others do not, is not really known. Whether it actually is the lack of light that is causing the symptoms is also unclear.  What is known is that light exposure through the eyes, either by the sun or by an artificial light source, is able to counteract reduced feelings of well being.

In people experiencing seasonal changes, bright light during the short winter days, and in particular during the morning hours, may fight the low energy levels and improve mood. Already 30 minutes of light is capable of increasing subjective energy levels.

If one recognizes the annual pattern in feelings of fatigue, increased sleep need and mild mood disturbances in winter, it seems optimal to start exposure to 20-30 minutes of bright light in the morning around breakfast time, as soon as the first signs in autumn appear.

Bright light entering our eyes is increasing our alertness, and decreasing sleepiness, and makes us feel more energetic.

This is so during the day and during the night. In the morning, when the eyes are still adapted to darkness, relatively moderate intensity of light, such as the one of Wake-up Light can be sufficient to activate the body and reduce sleepiness. During the day one needs to seek much brighter light to increase alertness, such as light provided by Philips EnergyLight devices, or of the bright sunny day.

In nature, daily life is innitiated by the upcoming Sun, and comes to rest after the Sunset. Modern society respects different daily schedules, we often need to get up before the sunrise, and continue activities till long after the sunset.

These natural gradual changes from dark to light and back to dark are, however, important cues for our bodies optimal functioning and for our sense of well-being. Philips Wake-up Light brings the essence of the natural sunrise to your bedroom: the gradual increase of light intensity before awakening is gently preparing the body for waking up, resulting in a more energized feeling and natural, easy rising. The overall sense of well-being is positively influenced by light and morning mood is improved. 

In modern society we have the capability to prolong the light part of the day by using artificial lighting. Our bodies are not synchronized to the rhythm of the Sun, but to our lifestyle.

Many people are extending their daily activities towards the evening, delaying their bedtime and, in case of work or school obligations on the next day, shortening their sleep. Insufficient rest has impact on daily functioning, and often it is only in the weekend when one tries to compensate for the sleep depth. Reducing the amount of light during the last few hours before bedtime and exposure to bright light in the early morning hours can support timely sleep start and more alertness and energy already at the start of the day. By maintaining a regular lifestyle with low variation of sleep times, sufficient light exposure during the day, low light exposure during the evening and darkness during the night, one can achieve a good balance between rest and activity and reduce a variety of health risks.

145 healthy participants have used Philips EnergyLight (2500 lux) for at least 1 hour per day and at least 5 days per week at their workplace during 2 (out of 4) of 4-week periods (the other 2 4-week periods they used no extra light at their workplace). Even for the participants with no seasonal variation of mood and energy the bright light exposure has improved vitality and mood when compared to the weeks without extra light.
Partonen, T. & Lönnqvist, J. Bright light improves vitality and alleviates distress in healthy people. Journal of Affective Disorders 57, 55–61 (2000).

This laboratory study compares the effects of bright light exposure (5000 lux) during the daytime and nighttime on different psychological and physiological measures. Whereas the impact the bright light has on different bodily functions varies depending on the part of the day, the effect of counteracting tiredness is universal during day and night.
Rüger, M. Time-of-day-dependent effects of bright light exposure on human psychophysiology: comparison of daytime and nighttime exposure. AJP: Regulatory, Integrative and Comparative Physiology 290, R1413–R1420 (2006)

Viola, A.U. et al. Blue-enriched white light in the workplace improves self-reported alertness, performance and sleep quality. Scand J Work Environ Health 34, 297–306 (2008)

The paper describes two sub-studies with Philips Wake-up Lights, evaluating (A) 2 week usage at home against waking up without light and (B) 2 week usage at home of different light intensities of the gradually increasing light (0 lux, 50 lux, and 250 lux). The main results from both groups confirm that waking up with gradually increasing light prior to the alarm time is of overall better quality than without light, the energy level of the users at wake-up is improved, participants reported easier rising, better mood, productivity, and quality of social interactions. A transient period of grogginess after awakening, called sleep inertia, was reduced when participants used Wake-up Light.
Gimenez, M. C. et al. Effects of artificial dawn on subjective ratings of sleep inertia and dim light melatonin onset. Chronobiology International 27, 1219–1241 (2010)

In how far can the effects of Wake-up Light be attributed to the gradually increasing light before the alarm time, and in how far it is the fact that the light is on when the eyes go open, was the central question of this controlled sleep laboratory study. It has shown that the alerting and activating effects are mainly linked to the gradual increase of light while the user is still asleep and that these effects can directly be sensed during the first use. Several physiological measures, such as skin temperature change at and after the wake-up follow the alerting dawn signal. Sleep recordings demonstrate that during the gradually increasing light period the users spend more time in the awake state prior to finally waking up then when they are spending the last 30 minutes of their sleep in darkness. On the average they finally woke-up only 2 minutes earlier than with the sound alarm only, but feeling more ready to wake-up. 
Van de Werken, M. et al. Effects of artificial dawn on sleep inertia, skin temperature, and the awakening cortisol response. Journal of Sleep Research 19, 425–435 (2010)

The new Philips Wake-up Light range uses LED technology, enabling tailored spectrum of light during the gradually increasing dawn signal, starting with deep red, then orange to yellowish white light at the end of the curve. The acute alerting effects of this new colored dawn were verified in a study at the University of Basel. Under controlled laboratory conditions it was for the first time shown that the light at and around wake-up time can have certain sustained effects on performance and wellbeing later during the day.
Gabel, V. et al. Effects of Artificial Dawn and Morning Blue Light on Daytime Cognitive Performance, Well-being, Cortisol and Melatonin Levels. Chronobiology International, 30(8), 988–997 (2013)

Wake-up Lights were used in a study with adolescents, 103 pupils between 7 and 18 years old. During the week they used Wake-up Light, pupils awoke earlier, felt more alert at awakening, got up easier and reported a higher alertness during the second lesson at school, compared to the week when they used their habitual way of waking up. Evening types benefited more than morning types, but the improvement was there for the group as a whole as well.
Fromm, E. et al. Evaluation of a dawn simulator in children and adolescents. Biological Rhythm Research 42, 417–425 (2011)