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Light performance

Future Designs conducted an experiment to find out how light affects our mood and work performance. Here are the results

From 10am on Tuesday 19 June until 10am on Wednesday 20 June, lighting expert Future Designs performed an experiment to test and analyse the effects of light on the circadian rhythms of two volunteers. The aim was to record how different types of light can affect human wake and sleep functions.

THE EXPERIMENT
Led by Future Designs’ consultant sleep expert, Dr Neil Stanley, the experiment took place at the company’s technology hub in Clerkenwell, London. Two separate areas of the hub were lit to extremes of the Kelvin band – cool versus warm light. The tones were created by Future Designs’ bespoke, digitally controlled wall-to-wall lit ceiling panels. One side was lit to 6000K in a cool white light, the other to 2700K of warm white light. The lighting was maintained throughout the day and night.

The volunteers, who were of similar age, height and weight, worked and slept in the window of the technology hub over a 24-hour period. Passers-by were encouraged to observe them and read about the experiment, dubbed Light Work Sleep.

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

THE RESULTS
Both volunteers completed 20 tasks several times throughout the 24-hour period to provide the data. The results were as follows:

⇒ Karolinska Sleepiness Scale (a measure of subjective sleepiness)

2700K produced lower levels of sleepiness across the entire experiment.

⇒ Card sorting task 1

6000K generally improved the time to complete this timed card sorting task.

⇒ Card sorting task 2

6000K generally improved the time to complete this task.

⇒ Psychomotor vigilance task (timed reaction task measuring the reaction to a number of stimuli which requires the subject to be vigilant to the appearance of the stimulus)

Overall, 6000K seemed to have a negative effect on reaction time to the stimulus.

⇒ Driving reaction time (timed reaction test)

Both lighting conditions improved the reaction time (they got quicker).

⇒ Number memory task

There appeared to be little effect on this task.

⇒ Word memory task (verbal memory test in which subjects state whether or not they have seen a word previously presented)

Overall, 6000K seemed to have a less negative effect on verbal memory.

⇒ Can-2 task (timed letter search in which the subject searches a grid of letters, cancelling occurrences of two stimulus letters. The score is the number of letters cancelled in two minutes)

Overall performance reduced in both conditions.

⇒ Can-6 task (timed letter search in which the subject searches a grid of letters, cancelling occurrences of six stimulus letters. The score is the number of letters cancelled in five minutes)

Overall, there was little constant effect under either condition.

 

The next set of data is derived from the Line Analogue Rating Scale, a subjective measure of mood.

⇒ Line Analogue Rating Scale: anxiety

Overall, 6000K seemed to produce less anxiety across the day.

⇒ Line Analogue Rating Scale: tiredness

Overall, 2700K produced less tiredness across the day.

⇒ Line Analogue Rating Scale: relaxation

The reaction was mixed, although 6000K produced more relaxation in the later part of the day.

⇒ Line Analogue Rating Scale: drowsiness

6000K produced much higher levels of drowsiness during the afternoon and evening.

⇒ Line Analogue Rating Scale: dizziness

Little effect could be seen on dizziness.

⇒ Line Analogue Rating Scale: happiness

Little effect was seen on happiness.

⇒ Line Analogue Rating Scale: clumsiness

6000K produced a much higher feeling of clumsiness across the day.

⇒ Line Analogue Rating Scale: sadness

There was little effect on sadness.

⇒ Line Analogue Rating Scale: alertness

Overall, 6000K produced much lower subjective alertness across the study, particularly in the afternoon and evening.

⇒ Line Analogue Rating Scale: energy

Overall, 6000K produced much lower feelings of energy during the day, particularly in the afternoon and evening.

⇒ Line Analogue Rating Scale: depression

Overall there was little effect on levels of depression.

About Sarah OBeirne

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