Lighting’s ability to affect mood and sleep is ‘limited’

THE ABILITY OF lighting to affect mood, alertness and sleep in real-world conditions may be limited as a result of differing personalities and motivation, the results of an experiment appear to show.

Led by sleep expert, Dr Neil Stanley, a consultant to Future Designs, the test took place on midsummer’s day to analyse the effects of light on the circadian rhythms of two volunteers, with the intention to record how different types of light can affect the human wake and sleep functions.

Two separated areas were lit to extremes of the Kelvin band - cool versus warm light. One side was lit to 6000 kelvin in a cool white light, the other to 2700 kelvin of a warm white light and both were lit throughout the day and night.

Two separated areas were lit to extremes of the Kelvin band - cool versus warm light. One side was lit to 6000 kelvin in a cool white light, the other to 2700 kelvin of a warm white light and both were lit throughout the day and night.

The two different lighting tones were created, digitally controlled wall to wall lit ceiling panels. The volunteers who were of similar age, height and weight worked and slept in the window of the Future DesignsTechnology Hub in London over a 24 hour period. Passer-bys were encouraged to observe the spaces and read about the experiment dubbed Light Work Sleep.

During the simulated working day, the volunteers had their memory, reaction time and vigilance measured regularly by Dr Stanley, and they were questioned about their mood and alertness. Their cognitive function was tested on the second morning and evaluated.

Surprisingly, 2700K produced lower levels of sleepiness across the entire experiment   while 6000K seemed to have negative effect on reaction time to the stimulus  in th

‘psychomotor vigilance task’, a timed reaction task measuring the reaction to a number of stimuli which requires the subject to be vigilant to the appearance of the stimulus.

The report – sponsored by UK luminaire manufacturer Future Designs – stated that ‘the realities of performing an experiment like Light Work Sleep in the window of a showroom presented some limitations and meant that controlling all the variables to a clinical level wasn’t possible.

‘Given that, we should not read too much into the results of the psychological tests, although the assessments indicated there were some clear differences between the two conditions on some of the tasks’.

Even under imperfect testing environs, it became clear that different lighting conditions can have a significant effect on performance, feelings of alertness and particularly on subjective mood.

During Light Work Sleep the 6000K cool white light subject felt less alert across the day, particularly in the afternoon and evening. This result could be thought as going against the theory that blue light is capable of producing alertness and improvements in performance.

While this may be the case in an ideal environment under more ‘real-world’ conditions, as seen in this experiment many other factors can also have an effect.

Prolonged exposure to 6000K cool white light, particularly in the afternoon and evening, may in itself be wearying given that it is the opposite to the natural changes in sunlight at this time, the researchers concluded.  ‘Additionally, exposure to sunlight may negate the relaxing effects of a simulated 2700k warm white light overhead’.

“Personality and motivation may play a big part, for instance a bright summer’s day causes some people to head to the mountains to hike and others to spend the day lying on a beach, therefore it is possible that there was a paradoxical effect to the 6000k cool white light environment.

‘Humans do not only use light as a zeitgeber (time-giver), we respond to other things such as social interactions and food intake. Although in our experiment we controlled the timings of food, the individuals’ response to feeding e.g. the joy of a nice meal as compared to an average meal could have played a part in their response to the situation.

‘Perhaps this is the most important take-away from Light Work Sleep. A vital contributing factor to the reactions of the volunteers is individual differences. While the subjects were matched for gender, age, build etc and conditions, other than the light, were as far as possible identical, the results are going to be heavily influenced by the differences in mood and sleepiness levels between the subjects.’

'For instance, looking at the KSS raw scores instead of looking at change from baseline we can see that our volunteer in the 2700K warm white light was quite sleepy at the start of the study compared to our volunteer in 6000k cool white light, thus she had less room for change in her scores of sleepiness under conditions that are thought to be more relaxing. I.e. the effect would have probably have had to be proportionally larger in her case for her to have noticed a measurable change. This could also explain why she showed less change in her Line Analogue Rating Scale measures related to alertness.

Dr Stanley sleep consultant concluded: ‘While tuneable white light may have the ability to modulate alertness and performance it is only one of many factors that affect our everyday life, the relative contribution of the effect of light on everyday alertness and performance needs to be elucidated’.



  • Human-centric lighting will be explored in the Workplace and Wellbeing Conference taking place at LuxLive 2018 on Thursday 15 November at London ExCeL. Entry is free if you pre-register HERE.