It seems rather self-evident that humans after adolescence are not nocturnal. When it gets dark people get tired. When it gets brighter we tend to wake up or stay awake. People can start having trouble getting to sleep or sleeping just because of lighting conditions, unrelated to other causes like medical conditions, taking drugs affecting sleep (like stimulants), or stress, or noise, or… Light is not the only zeitgeber, but the latest scientific consensus says:
23.2 Light therapy
Our modern inventions have granted us control over our lighting environment (Fig. 23.2). We can choose to stay awake and surf the Internet by peering into our blue backlit screens all night if we want, or to retreat into dark, cool shelters of Abercrombie shops or watch the game at a local bar during the day. The temporal restructuring of light can lead to a state of circadian disruption, exposing us to new health risks and disease. Light is the most potent environmental cue able to predictably phase shift the timing of behavior (Khalsa et al., 2003). It is detected by the photopigment melanopsin localized in intrinsically photosensitive retinal ganglion cells (ipRGCs). Melanopsin is most sensitive to blue wavelengths of light and its activation leads to the release of glutamate onto the SCN via the retinohypothalamic tract (Schmidt et al., 2011; Lucas et al., 2012). The glutamate signaling causes immediate molecular and cellular changes in the SCN, including increases in firing rate and the induction of c‐fos and Per1 transcription that eventually lead to a shift in the timing of the molecular clock within the SCN and throughout the body (Chapters 1 and 2).
In diurnal animals, exposure to even low intensities of blue light during the night can interfere with sleep by inhibiting sleep‐promoting neurons, acutely reducing melatonin levels, activating arousal‐promoting orexin neurons and stimulating the sympathetic axis (Duffy and Czeisler, 2009; Ruger and Scheer, 2009; Adidharma et al., 2012). In addition to poor sleep quality, light at night reduces daytime alertness the following day. Over a long period of time, these aberrant light cycles can increase the risk for serious diseases. Therefore, methods or behaviors that help reinforce the timing of natural, environmental light and maintain the normal variance of light intensities between night and day would reinstate a more robust and stable circadian system. Strengthening of the circadian network and enhancing circadian control of tissue function and physiology, will likely restore restorative sleep as well as daytime alertness helping to improve daily life and reducing the risk for disease.
In practice, light therapy has been demonstrated to ameliorate circadian symptoms in some conditions, including advanced/delayed sleep phase syndrome, jet lag, shift work, seasonal affective disorder and depression (Burgess et al., 2002; Barion and Zee, 2007). The scheduled light exposure helped reestablish the daily sleep–wake cycle and improve mood (Magnusson and Boivin, 2003; Wirz‐Justice et al., 2004). The positive outcome is encouraging the use of light therapy for other conditions that present with circadian symptoms, including aging and neurodegenerative diseases. In these groups, light therapy improved daytime alertness and sleep (Lieverse et al., 2011; Friedman et al., 2012; Royer et al., 2012; Rutten et al., 2012) and enhanced motor and cognitive abilities (Yamadera et al., 2000; Ancoli‐Israel et al., 2003; Riemersma‐van der Lek et al., 2008; Willis et al., 2012). Individuals suffering from major depression show improvements in mood when light therapy is included in the treatment regimen (Benedetti, 2012; Chapter 17).
However, other studies show no or small changes in objective and subjective measures of sleep (Ancoli‐Israel et al., 2002; Friedman et al., 2009). These discrepancies point out that a better understanding is needed of critical parameters such as light wavelength, intensity, and duration, as well as the timing of treatment, relative to the endogenous circadian rhythm. But it is worth re‐emphasizing that even young, healthy individuals can be influenced by improved light exposure (Viola et al., 2008). A study found that camping in the beautiful mountains of Colorado and exposure to natural lighting for several days was effective in advancing the phase of melatonin rhythms in young adults by two hours (Wright et al., 2013). Thus lighting conditions provide one of our most powerful tools to influence the circadian system.
(Christopher S. Colwell: "Circadian Medicine", Wiley-Blackwell: Hoboken, 2015, p 339–340.)
So, less light overall is good for sleep. But then only "overall" if temporally related to wanting to sleep soon. Conversely, more light during the day also helps maintaining a healthy circadian rhythm. This rhythm of wake and sleep seems to be almost more important to keep relatively steady than getting enough natural daylight and sleeping in the dark.
(Charmane I. Eastman et al.: "Dark Goggles and Bright Light Improve Circadian Rhythm Adaptation to Night-Shift Work", Sleep, Volume 17, Issue 6, 1 September 1994, Pages 535–543, https://doi.org/10.1093/sleep/17.6.535)
Guessing it does not count as science-related: electronic devices are so bad for your healthy sleep that even Apple offers now a redshifting feature in newer machines. But that is partially because: Evening use of light-emitting eReaders negatively affects sleep, circadian timing, and next-morning alertness:
Moreover, the observation that the endogenous circadian melatonin
phase was 1.5 h later when reading an LE-eBook compared with reading
from a printed book suggests that using a light-emitting device in
the hours before bedtime is likely to increase the risk of delayed
sleep-phase disorder and sleep onset insomnia, especially among
individuals living in society who self-select their bedtimes and wake
times. Induction of such misalignment of circadian phase is likely to
lead to chronic sleep deficiency.
Although it also was quite a small sample: any light at night is not so good, but blue light is the worst.
The American Medical Association's Council on Science and Public Health: "recognizes that exposure to excessive light at night, including extended use of various electronic media, can disrupt sleep or exacerbate sleep disorders, especially in children and adolescents. This effect can be minimized by using dim red lighting in the nighttime bedroom environment."
Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans
Joshua J. Gooley, Kyle Chamberlain, Kurt A. Smith, Sat Bir S. Khalsa, Shantha M. W. Rajaratnam, Eliza Van Reen, Jamie M. Zeitzer, Charles A. Czeisler, Steven W. Lockley J Clin Endocrinol Metab. 2011 March; 96(3): E463–E472. Published online 2010 December 30. doi: 10.1210/jc.2010-2098
Sensitivity of the human circadian pacemaker to nocturnal light: melatonin phase resetting and suppression
Jamie M Zeitzer, Derk-Jan Dijk, Richard E Kronauer, Emery N Brown, Charles A Czeisler
J Physiol. 2000 August 1; 526(Pt 3): 695–702. doi: 10.1111/j.1469-7793.2000.00695.x PMCID: PMC2270041
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The "ideal lamp" shortly before bedtime is easily any lamp that is powered off. The evidence is growing that a lamp that simulates dawn shortly before bedtime is on second place. Dawn is meant here as: decreasing intensity and a reduction in the available spectrum: less blue light or a shift towards the "red" end of the spectrum.
From an environmental standpoint sadly the incandescent lightbulbs of old, coupled with an automatic dimmer-timer would be close to ideal. With modern LEDs things get complicated again since they typically emit rather specific wavelengths of light. Switching to red and yellow LEDs towards night seems necessary, choosing an LED-bulb advertised with "warm" light characteristics would come next. Standard LEDs and "bright", "cold" lights are not really advisable towards bedtime.
