Light performance

CONCLUSION
The realities of performing an experiment like Light Work Sleep in the window of a showroom created 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 clear differences between the two conditions on some of the tasks.

Even in this imperfect test environment, 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 appears to contradict 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, this experiment suggests many other factors have an effect.

Prolonged exposure to 6000K cool white light, particularly in the afternoon and evening, may be wearying given that it is the opposite to the natural change in sunlight at this time. 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 example, a bright summer’s day causes some people to head to the mountains to hike while others want to spend the day lying on a beach, which means it’s possible that there was a paradoxical reaction 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 interaction and food intake. Although in this experiment consumption of food was timed, the individuals’ response to feeding – the joy of a nice meal as compared to an average meal, for example – could have played a part in their responses.

Perhaps this is the most important take-away from Light Work Sleep. Individual differences were a vital factor in the volunteers’ responses. While the subjects were matched for gender, age and build, and ambient conditions were as far as possible identical, the results were probably 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 noted 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. This meant she had less room for change in her sleepiness scores under conditions that are thought to be more relaxing (in other words, the effect would probably have had to be proportionally larger for her to have noticed a measurable change). This could also explain why she showed less change in her Line Analogue Rating Scale alertness score.

In summary, Dr Stanley explains: “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.”

All data is expressed as change from baseline.