The primary function of a hotel is to ensure a good night’s sleep for its guests. Ideally, that means room lighting that does not keep its occupants awake. Soft, muted lighting in attractive warm tones will get the job done. Right?
Not necessarily. Now that we have begun to understand the biological effects of light, it appears that a lot of human wakefulness is self-inflicted. Our biological clocks tell us when to wake up, when to become tired, and when to fall asleep. These responses are controlled by the colour and brightness of the light around us. Specifically, high-intensity light that contains a lot of blue makes us feel awake and alert, while its absence helps us to sleep.
"Bright light with high levels of blue is counterproductive in the evening and at night”
Natural vs artificial
We’re meant to start feeling drowsy as the sun sets, when light drains from the sky and cool blue gives way to warm red. This triggers the release of the sleep hormone melatonin and it’s heads down for a good night’s kip. But what we actually do is confuse our biological clock by switching on artificial lights, letting us remain active long after darkness falls.
Research shows that any lighting in the evening or at night shuts down melatonin production. Luc Schlangen, senior scientist at Philips Lighting, explains: ‘The photoreceptors in our eyes, even with eyes the shut, only need to detect a few pulses of light for the body to suppress melatonin production and promote wakefulness.’
The brighter the light, the more extreme the effect – and it’s worse if the light has a strong blue component (which most LED lights do). It means the body doesn’t get the sleep memo until much later. And night lights are an absolute no-no. ‘Melatonin is only produced when you sleep in complete darkness,’ says Schlangen.
Room lighting that is too bright or too blue is not the only problem. Research suggests that the blue spectrum light emitted by TV, computer and smartphone screens and other gadgets also suppresses melatonin. To test this, researchers from Harvard Medical School locked a group of people in a sleep lab for two weeks, some with a paper book for company, others with an iPad. The participants with the iPads produced less melatonin than those with paper books and took longer to get to sleep.
Clearly no hotel is going to remove TVs from rooms, confiscate phones and advise guests to go to bed with a good book. Nor is it going to hand out oil lamps and candles. So what can be done to make bedroom lighting more biologically friendly?
To answer this question, Osram joined forces with the Bergisch University of Wuppertal in Germany to find out if the use of special chronobiological lighting (lighting adapted to biological rhythms) would help hotel guests feel more awake and active in the day and sleep better at night. The study was carried out in the Jammertal Golf and Spa Resort hotel in Datteln, Germany.
One group of 40 people was exposed to standard hotel lighting conditions, and a second group spent two days in lighting conditions designed to simulate the natural sky. The response of the two groups was tested using long-term ECGs, motion sensors, and measurement of cortisol and melatonin levels.
The results showed that the chronobiologically adapted lighting reduced symptoms of stress, fatigue and discomfort in the test group during the study period. The quality of sleep was increased and night-time restlessness reduced due to a rapid reduction of melatonin level in the morning and a rapid rise in the evening. The test group also reported feeling less tired during the day.
The study highlighted the fact that a healthy circadian sleep cycle is not just about dropping off to sleep. It’s also about waking feeling alert and refreshed. And that requires a dose of bright cold light (‘activating’ light) during the early part of the day.
Andreas Wojtysiak, senior light and health scientist at Osram, explains: ‘Bright light with high levels of blue light is counterproductive in the evening and at night, disturbing the circadian system and reducing sleep quality. But warm white light at low illuminance levels is not appropriate for the morning and day because it does not stimulate the body clock and circadian system to toggle between recovery (night) mode and activated (day) mode.’
"To ensure a smooth transition from wakeful to sleepy and back again, hotel guests need a nice warm glow in the evening and high-intensity cool light during the day"
Day and night
In other words, to ensure a smooth transition from wakeful to sleepy and back again, our hotel guest requires a nice warm glow in the evening and high-intensity cool light during the day.
Luminaires exist that address specific stages of the circadian rhythm; Philips’ LED-based Wake-Up Light, for example, gradually increases light levels over 30 minutes to ensure a gentle, natural waking process. But we could be waiting some time for a smart lighting system capable of managing individual sleep cycles around the clock, catering for both night owls and morning larks.
‘We do not recommend an optimum sleep cycle because what is right for one person may not be right for another,’ says Philips’ Luc Schlangen. ‘Our research shows that it is near impossible to recommend an ideal sleep-wake cycle for anyone because we do not all have the same natural circadian rhythm. While we know that most people have a longer circadian rhythm than our 24-hour artificial clock, within this group the variation is vast.’
Realistically, then, what is the best approach for the hotel operator keen to do right by its guests? ‘A general room light that is dimmable and can provide warm white colours, plus ideally an orientation light, yellow to red, that is controlled by a sensor or switchable, to avoid falls when being up in the night,’ suggests Andreas Wojtysiak. ‘A spot-like luminaire would give warm white light for reading.
‘For the morning, a light that slowly dims up before you are awake to ease the wake-up process. During the day, a cool white light with high light levels – if significant time is to be spent there during the day.’