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Mental activation and sleep

From "Effect of Illuminance and Color Temperature on Lowering of Physiological Activity"

"...we surmise that the effect of color temperature is greater than that of illuminance in an ordinary residential bedroom or similar environment where a lowering of physiological activity is desirable, and we therefore find the use of low color temperature illumination more important than the reduction of illuminance. Subjective drowsiness results also indicate that reduction of illuminance without reduction of color temperature should be avoided."
These results suggest that low color temperature light creates a smooth lowering of central nervous system activity, and that low color temperature illumination can be used effectively in a bedroom or other such environment where it is desirable to facilitate lowered physiological activity.

From "Effect of Color Temperature of Light Sources on Slow-wave Sleep", Tomoaki Kozaki [1], Shingo Kitamura [2], Yuichi Higashihara [2], Keita Ishibashi [1], Hiroki Noguchi [3] and Akira Yasukouchi [1]

1. Department of Physiological Anthropology, Faculty of Design, Kyushu University
2. Department of Ergonomics, Kyushu Institute of Design
3. Matsushita Electric Works, Ltd.
Seven healthy males were exposed to the light sources of different color temperatures (3000 K, 5000 K and 6700 K) for 6.5 h before sleep. The horizontal illuminance level was kept at 1000 lux. Subjects slept on a bed in near darkness (<10 lux) after extinguishing the light, and polysomnograms recorded the sleep parameters. In the early phase of the sleep period, the amount of stage-4 sleep (S4-sleep) was significantly attenuated under the higher color temperature of 6700 K compared with the lower color temperature of 3000 K. Present findings suggest that light sources with higher color temperatures may affect sleep quality in a view that S4-sleep period is important for sleep quality.

From "The effect of high correlated colour temperature office lighting on employee wellbeing and work performance", Peter R Mills (1,2) , Susannah C Tomkins (1) and Luc JM Schlangen (3)

1. Vielife Ltd, 68 Lombard Street, London EC3V 9LJ, UK
2. Department of Respiratory Medicine, The Whittington Hospital, London N19 5NF, UK
3. Philips Lighting, Global Organisation Applications Lighting, P.O. Box 80020, 5600JM Eindhoven, The Netherlands

Journal of Circadian Rhythms 2007, 5:2doi:10.1186/1740-3391-5-2
The amount of blue light in the spectrum of light sources increases with increasing colour temperature. So far a number of studies have investigated the effects of the colour temperature of lighting on mental activity, the central nervous system and alertness. These studies have demonstrated that higher colour temperatures (7500 K versus 3000 K) are more activating from the viewpoint of mental activity level [12]. Both the parasympathetic and sympathetic nervous systems are thought to be enhanced under higher colour temperature conditions. [13] and drowsiness has been observed to be higher under lower colour temperature lighting when comparing 3000 K with 5000 K [14].

From "Effects of indoor lighting (illuminance and spectral distribution) on the performance of cognitive tasks and interpersonal behaviors: The potential mediating role of positive affect"

In Study 2, subjects exposed to warm white light reported stronger preferences for resolving interpersonal conflicts through collaboration and weaker preferences for resolving conflicts through avoidance than subjects exposed to cool-white light. Additionally, illuminance and spectral distribution (color) interacted to influence subjects' self-set goals on a clerical coding task. In Study 3, receipt of a small, unexpected gift and exposure to warm-white light both increased the amount of time subjects were willing to donate as unpaid volunteers. In addition, in the absence of a gift, subjects volunteered more time under low than under high illuminance.

Terman and Terman report in "Light Therapy for Seasonal and Nonseasonal Depression: Efficacy, Protocol, Safety, and Side Effects" in CNS Spectrums:

Recent attention has focused on the blue region, which actively suppresses melatonin production (23) and elicits circadian rhythm phase shifts. (24, 25) In a comparison of blue light with red light of lower intensity (designed as a placebo control), the antidepressant response to blue was superior, similar to that seen for white light in other studies. (26)

23. Brainard GC, Hanifin JP, Greeson JM, et al. Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor. J Neurosci. 2001;21:6405-6412.

24. Wright HR, Lack LC, Kennaway DJ. Differential effects of light wavelength in phase advancing the melatonin rhythm. J Pineal Res. 2004;36:140-144.

25. Warman VL, Dijk DJ, Warman GR, Arendt J, Skene DJ. Phase advancing human circadian rhythms with short wavelength light. Neurosci Lett. 2003;342:37-40.