FUTURE Designs with the help of consultant sleep expert, Dr. Neil Stanley, conducted an experiment comparing long-term exposure to cool versus warm light. The study looked at two women who were of similar age, height, and weight. One was exposed to warm LED light. The other was exposed to cool LED light.
Contrary to what the industry seems to portray, the results of the study looking at cognitive ability and alertness were not as predicted. Instead of a straightforward result, the limited study should much more nuanced effects of lighting on cognitive ability and levels of alertness.
Methods of Experiment
The experiment illuminated two separated areas of the Technology Hub to extremes of the Kelvin band, cool (6000K) versus warm light (2700K). The different light tones both came from FUTURE Designs custom-designed, digitally controlled wall-to-wall lit ceiling panels. Both areas were illuminated throughout the day and night. For the test, the volunteers worked and slept in the window of the Technology Hub over a 24 hour period. Pedestrians passing bys were encouraged to watch the spaces and read about the experiment dubbed Light Work Sleep.
During the simulated working day, Dr. Neil Stanley regularly measured the memory, reaction time and vigilance of the volunteers. Then, he questioned them about their mood and alertness. Dr. Stanley also tested and evaluated their cognitive function on the second morning. Both volunteers completed 20 tasks, several times throughout the 24-hour period to provide data.
Results of Experiment
Using the Karolinska Sleepiness Scale, a measure of subjective sleepiness, the 2700K LED light produced lower levels of sleepiness across the entire experiment. This result seems particularly contrary to conventional wisdom surrounding the use of color temperature to alter alertness levels.
However, for the two different card sorting tasks, the 6000K generally reduced the amount of time the tasks took.
Dr. Stanley also conducted a 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 the 6000K light appeared to have increased (slowed) the reaction time to the stimulus.
On the other hand, for the Driving Reaction Time test, both lighting conditions seemed to improve (speed up) the reaction time over the course of the experiment.
For the Number Memory Test, the lights appeared to have little effect on the results. Nevertheless, on a Word Memory Task, which involved saying whether you have or have not seen a word previously presented, both participants got worse over the course of the test. However, the 6000K light seemed to have a less of a negative effect overall on verbal memory than the 2700K lighting.
Another test which both participants seemed to get worse on over the course of the experiment, was the timed letter search. This task involved searching a grid of letters and canceling out the occurrence of the 2 stimulus letters. The score is the number of letters canceled in 2 minutes. Overall both reduced performance over time. Despite this, in a similar test, another timed letter search, which involved searching a grid of letters and canceling occurrence of the 6 stimulus letters over five minutes, found little constant effect under either condition.
Subjective Measurement of Mood
As part of the experiment, Dr. Stanley gave the two participants the Line Analogue Rating Scale. The Line Analogue Rating Scale a survey about their mood and that asks subjects to rate aspects of their mood on a scale.
According to the results derived from this subjective survey, Overall 2700K produced less tiredness throughout the day. The participants indicated that their feelings of relaxation were mixed over the two color temperatures, but 6000K seemed to elicit more feeling of relaxation in the later part of the day.
Contrary to popular belief, 6000K produced much higher levels of drowsiness during the afternoon and evening. And consequently, 6000K seemed to produce much lower levels of perceived alertness and energy as well. The 6000K light also seemed to have a negative impact on perceived clumsiness.
Subjective measures of depression, sadness, and happiness were not affected by either light condition.
Possible Reasons for Contrary Results
Stanley suggested that one of the reasons for the results contrary to conventional wisdom could be the difference’s in the individual participants. One of the participants was in fact quite sleepy at the start of the study.
Stanley also suggested that prolonged exposure to 6000K cool white light, especially in the afternoon and evening, may be wearying due to it being the opposite of the natural changes in sunlight at this time.
So, in conclusion, Dr. Neil Stanley sleep consultant for FUTURE Designs explained, “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.”