The Effects of Red and Blue Light on Alertness and Mood at Night
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Lighting Res. Technol. 2010; 42: 449–458 The effects of red and blue light on alertness and mood at night B Plitnick RN, MG Figueiro PhD, B Wood and MS Rea PhD FSLL Lighting Research Center, Rensselaer Polytechnic Institute, 21 Union Street, Troy, NY 12180, USA Received 23 October 2009; Revised 18 December 2009; Accepted 28 December 2009 This study was designed to explore the roles that long- and short-wavelength lights have on momentary mood and alertness at night. Twenty-two subjects participated in a mixed-design experiment, where we measured the impact of two levels of long- and short-wavelength lights on brain activity and on self- assessments of alertness, sleepiness and mood. Measurements were obtained 60 minutes prior to, during and after light exposure. Results showed that the red and the blue lights increased electroencephalographic beta power (12–30 Hz), reduced sleepiness, and increased positive affect relative to the previous dim-light period indicating that alertness and mood can be affected by light without necessarily stimulating the melatonin pathway. The impact of light was modest, however, compared to the increase in fatigue over the course of the night. 1. Background changes in momentary mood and alertness because optical radiation incident on the Environmental stimuli can affect momentary retina has multiple effects on brain activity mood and alertness. The impact of colour on through parallel neural pathways. momentary mood and alertness is still con- For example, some studies suggest that troversial, at least in part because of the colours seen as ‘warm’ (red, orange, yellow) confusion between three distinct domains, evoke feelings of arousal while colours seen as physical, physiological and psychological. ‘cool’ (violet, blue, green) are associated with Strictly speaking colour is not a stimulus, calming feelings. The colour red, for example, but rather a psychological result of processing has been associated with feelings of danger, by neural mechanisms of the spectral irra- love, rage and excitement as well as negative diance distribution (SID) incident on the feelings such as anxiety, anger and annoy- retina. Some authors suggest that apparent ance. It has been suggested that the colour red colour itself affects momentary mood and increases human receptiveness to external alertness. Other studies have examined the stimuli and increases excitation, therefore impact of different SIDs on hormone pro- affecting a person’s emotional and motor duction and electrical brain activity asso- responses.1,2 Goldstein has argued that red ciated with momentary mood and alertness colours, though arousing, impair perfor- without specific regard to the apparent colour mance on complex activities in which exact- those stimuli evoke. It is usually very difficult, ness is required. The colours green and blue however, to determine the underlying have been associated with feelings of relax- mechanisms contributing to light-induced ation and calmness.2–6 Elliot et al.7 performed a series of studies to investigate the impact of red colour on Address for correspondence: MG Figueiro, Lighting Research performance in achievement contexts, that Center, Rensselaer Polytechnic Institute, 21 Union Street, Troy, NY 12180, USA. E-mail: [email protected] is, in situations in which competence is ß The Chartered Institution of Building Services Engineers 2010 10.1177/1477153509360887 450 B Plitnick et al. evaluated and positive and negative outcomes effect that short-wavelength light is also seen are possible. They hypothesised that red as blue in these studies. This assumption has colour is associated with danger of failure, justification because the results of recent and therefore, there would be an automatic, studies using short-wavelength light as a unconscious decision to avoid the object, stimulus for enhancing alertness and perfor- situation or events. Their findings supported mance and reducing sleepiness are entirely the hypothesis that perception of red colour consistent with the neurophysiological evi- prior to an achievement task impairs perfor- dence that neural pathways from the SCN are mance compared to a green and an achro- important to sleep and alertness.13 These matic colour. Similar findings have been converging lines of research add weight to reported by Stone.8 These results are not the inference that the SCN, through retinal consistent with findings by Hill and Barton,9 stimulation by short-wavelength light, plays however, who reported that red enhances an important role in human alertness and performance of athletes who wore red colour. probably performance. Very recently, how- 14 In general, the studies of colour on emotions ever, Figueiro and colleagues showed that and performance are conflicting. Although the circadian system may not be the only part of the explanation for this lack of pathway associated with light-induced alert- consistency may be due to random, non- ness at night. They showed that both long- systematic effects of apparent colour on wavelength, red light and short-wavelength, human physiology and behavior, or to indi- blue light of the same corneal illuminance vidual differences in apparent colour prefer- evoked similar alerting effects (i.e. increased ence, or to differences in cultural associations power in the electroencephalogram (EEG) with apparent colour,10 some of the uncer- beta frequencies and reduced power in the tainty must arise from a failure to define the EEG alpha frequencies). light stimulus independent of the psychologi- The goal of this study was to expand on cal response that the stimulus evokes, that is, that work by Figueiro and colleagues by its apparent colour. Without a characteri- investigating the impact of long-wavelength, sation of the stimulus independent of the red and short-wavelength, blue light on mea- response it evokes, it is not possible to develop sures of sleepiness and momentary mood an understanding of the physiological (both measured subjectively). The present study was expected to serve as a partial mechanisms mediating the measured outcome. validation of the previous results as well as Other studies have examined the impact of to investigate the dissipation of the alerting SIDs (combinations of both spectrum and effects of light after exposures to blue and irradiance), not simply apparent colour, on red lights. alertness, sleepiness and performance.11,12 Of particular interest for the present study, several studies have examined the impact of 2. Methodology short-wavelength light on nocturnal alertness and performance as it might be mediated by In order to minimise differences in cultural the suprachiasmatic nuclei (SCN), the pace- biases toward colours, 24 native-born subjects maker for regulating circadian rhythms. from the United States (19–27 years of age) Short-wavelength light is an important stim- were recruited to participate in the study ulus to the human circadian system; it is from an electronic posting at Rensselaer known to be maximally sensitive to short- Polytechnic Institute in Troy, New York. wavelength radiation peaking at about All subjects were screened for major health 450 nm. Presumably, it is only a collateral problems and except for women taking birth Lighting Res. Technol. 2010; 42: 449–458 Effects of light on alertness and mood at night 451 control pills, subjects reported not taking affecting the spectral irradiance distributions any pharmaceuticals or medications. Every of the LEDs. Measurements of pupil area subject completed a Munich Chronotype completed after the experiment with a differ- Questionnaire (MCTQ) prior to the study; ent group of subjects (N ¼ 5) were: red at those who were late or extremely late 10 lx, 34 mm2; red at 40 lx, 22 mm2; blue at chronotypes were excluded from the experi- 10 lx, 10 mm2; blue at 40 lx, 6.5 mm2. ment. This study was approved by the The Biosemi ActiveTwo system with active Rensselaer Polytechnic Institute Institutional electrodes was used for EEG recordings. This Review Board. Subjects were asked to refrain system is battery powered, minimising elec- from alcohol and caffeine on the days of the trical interference from alternating current experiment and were asked not to sleep after (ac) during recording sessions. Electrodes awakening for the day. Subjects were also were placed on subjects’ scalps according to asked to go to bed no later than 23:00 the night the International 10-20 system at Oz, Pz, Cz before the experiment. Of the 24 individuals and Fz.15 Two additional electrodes serving recruited for the study, 22 (9 males and as virtual reference electrodes for those 13 females) subjects completed the entire attached to the scalp were attached to the experiment and their results are reported right and to the left earlobes. Another elec- here. Two subjects decided to withdraw from trode was placed approximately 5 cm below the experiment after the first session. the left clavicle to measure an electrocardio- Four experimental lighting conditions, two gram (ECG) signal. spectra (blue and red) at two levels (10 lx and To minimise introducing personal biases 40 lx), were delivered to individual subjects associated with colour into the experiment, from 0.6 Â 0.6 Â 0.6 m3 light boxes, each fitted a mixed-design experiment was conducted with arrays of light-emitting diodes (LEDs). whereby half the subjects only saw blue light The arrays (ICove, Colour Kinetics) were and half the subjects only saw red light. located behind the front box apertures to be Subjects were given the same instructions outside the subject’s direct view, thereby before starting the experiment during which creating a uniform, non-glaring distribution they were informed that the light colour they of light within the box. During light expo- would be seeing (red or blue) was known to sures, subjects placed their chin on a rest have an alerting effect and that we were mounted near the front of a box, ensuring investigating the impact of light level. The delivery of the prescribed light exposure. The light stimuli were approximately equated in spectral emissions of the blue LEDs peaked at terms of visual response (i.e.