Software to better replicate natural daylight on screens

I will just check my emails one more time before I go to sleep. The bedroom is lit up with ghostly blue light as I scroll through the emails that arrived over the 30 minutes or so since I last checked. Sad but true and research suggests that I am not alone. Apparently, 95 per cent of us use some type of computer/smartphone at least a few nights a week within the hour before bed. Parallel research suggests that 63 per cent of the population experience ‘inadequate’ sleep. Could the two be related?

Evidence for the role of light in synchronising circadian rhythms in animals has existed since the work of Hastings and Sweeney in 1958. They reported that the circadian rhythm of a marine dinoflagellate Gonyaulax polyedra was reset by short wavelength (blueish) light. This paper gathered dust for a few decades as no one thought that these findings held any relevance for humans, whose circadian rhythms were then widely believed to be independent of light.

Research over the past two decades has changed all that and there is now good evidence that both the ‘quantity’ and wavelength of light play a crucial role in setting the human circadian rhythm. A full review of this topic will be included in a forthcoming CET article in Optician – here the author provides sufficient background to provide a rationale for a new software utility known as PC Sun Screen.

Retinal role in the body clock

A milestone in the research in this area was the discovery of photosensitive ganglion cells in 1998. Russell Foster and his colleagues, using mice without rods and cones, was the first to demonstrate that the body clock was preserved in the absence of the ‘normal’ photoreceptors, strongly suggesting the existence of a new receptor type. A rare sub-type of retinal ganglion cell bearing a photopigment known as melanopsin was eventually identified as a possible candidate. Subsequent studies confirmed that these cells projected to the suprachiasmic nucleus (SCN), (an area of the brain known to play a vital role in regulating circadian rhythms) and were indeed intrinsically photosensitive. Furthermore, when these ganglion cells were ‘knocked out’ in mice, the animals were unable to synchronise their circadian rhythms. This provided the last crucial piece of evidence linking these ganglion cells to circadian behaviour.

Subsequent research has shown that approximately 40 per cent of these cell’s axons project to the SCN while the rest project to regions of the brain that are involved in, among other things, sleep and hormone regulation. Evidence that light can impact on various physiological functions has been increasing, with studies showing effects on heart rate, core body temperature, sleep patterns, cortisol production, alertness, reaction time and attention, to name but a few.

The spectral sensitivity of this mechanism has been the subject of some debate. Melanopsin itself has a peak absorption at about 480nm, but there is now good evidence that the response of the intrinsically photosensitive retinal ganglion cells is also influenced by surrounding rods and cones. The relative contribution of the various photoreceptors seems to be context dependent, which makes it difficult to characterise the exact spectral response of the channel. However, suffice to say in this context that it shows a preferential response to blueish light.

Appreciation of this basic biology has led to the development of a number of therapeutic interventions. Light is now used to treat seasonal affective disorder (SAD) and appropriately timed light exposure is also used to treat sleep disorders. Light therapy has also been proposed for the treatment of depression, menstrual-cycle related problems and various cognitive and fatigue-related disorders.

Lighting environment

These inherent mechanisms to synchronise various physiological and behavioural systems to light have presumably evolved over millennia during which natural light was the only source of illumination and therefore the quantity and spectral content (colour) of light provided a reliable temporal reference.

Daylight follows a daily cycle with the illumination increasing from dawn until approximately midday and then decreasing until dusk. Furthermore, the spectral content varies as the path length through the atmosphere changes. At sunrise and sunset, the light has further to travel through the atmosphere and, as the short wavelengths (blues) are scattered more than the longer wavelengths, sunlight has lower blue content (and therefore appears relatively orange/red) towards dawn and dusk (Figure 1).

The advent of artificial light sources and display screens has disrupted this age-old mechanism. Not only can we illuminate our surroundings to levels approaching those of natural daylight long after the sun has set, but we have lost the natural cue provided by the change in the colour of the light.

Recent moves to introduce ‘energy efficient’ light sources have further diminished the natural light cue. The relatively dim ‘orangey’ light produced by conventional tungsten lamps is being replaced by the relatively blue light and higher illumination levels provided by the new light sources.

There are a number of ways in which the spectral content of artificial light can be modified. The lighting industry has started to address these problems by filtering the emitted light to give the desired spectral content. The traditional objectives of lighting design of optimising visual comfort and performance now need to include consideration of the other effects of light on physiology and behaviour. However, until the illumination level and spectral content of lamps can be automatically adjusted according to the time of day, it is difficult to conceive of a solution that will work in all situations at all times of the day.

A variety of blue-blocking tints and filters are also being promoted as a solution. While these may be effective at reducing the blue content of light and thus help if worn in the evening, they might reduce alertness and other positive behavioural responses if worn during the day.

The increasing use of computers, tablets and smartphones in the hours before sleep provides further disruption to the natural pattern of light. The exact impact of this unnatural interference with the diurnal variation in both the level and spectral content of light, is difficult to tease out. However, there is growing evidence that the spectral profile of light emitted by computer screens impacts on circadian physiology, alertness and cognitive performance levels. There is also some evidence that exposure to the relatively blue light emitted by LED-based displays impacts on the length and quality of sleep.

A number of programs/apps are available to change the spectral distribution of the light emitted from electronic devices so that it is more closely matched to natural daylight. For example, F.Lux is a simple program which adjusts the colour temperature of the screen according to the time of day. It is available for PCs, Macs, iPhones and iPads and, according to the website, has been installed on many hundreds of computers. However, the available apps offer limited control over the timing of the changes in screen colour and the exact screen hue. Furthermore, the screen ‘tint’ cannot be easily removed (as may be required for certain colour sensitive tasks) and is always applied across the whole screen.

PC Sun Screen

PC Sun Screen, developed by Thomson Software Solutions, is a powerful new utility which provides PC users with complete control of the hue of their computer screen by placing a ‘virtual filter’ over the screen. The colour of the virtual filter gradually changes between the preferred daytime colour (usually blue) and the preferred night time colour (usually orangey/red) so that the overall hue of the screen mimics natural daylight (Figure 2). The screen colour imperceptibly changes from having a slightly blue hue during the day to an orangey hue in the hours leading up to sleep time.

A unique feature of the software is that it allows the preferred ‘sleep time’ and ‘wake time’ to be set so that the transition of screen colours is optimised for the user’s normal sleeping patterns – particularly useful for shift workers. The program also allows the user to specify the preferred colour and density for the daytime and night time filters to accommodate personal preferences and differences in the colour reproduction of monitors (Figure 3).

Another unique feature of the software is the ability to define different coloured filters for each monitor when using multiple display systems. This is useful for accommodating differences in colour reproduction between monitors.

A potential disadvantage of tinting the screen is that it inevitably causes some distortion of on-screen colours. For applications where accurate colour reproduction is crucial, normal screen colours can be restored at the click of a button. In addition, PC Sun Screen uniquely allows the filter to be moved and resized so that colour critical areas (such as palettes) are not covered by the filter.

Such programs do not provide a complete solution as clearly any benefit bestowed by changing the colour of the screen will be undone if the user is then exposed to relatively blue room lighting. Therefore consideration also needs to be given to managing exposure to other light sources in the evening.

There is now overwhelming evidence that the quantity and spectral content of light are important in synchronising circadian rhythms. There is also strong reason to believe that exposure to bright displays screens with relatively high blue content have the potential to disrupt this mechanism and affect sleep patterns; the research evidence that this is the case is growing. In the meantime, programs such as PC Sun Screen have a growing and enthusiastic band of users who claim that the natural progression of screen colours throughout the day improves viewing comfort and the quality of sleep.

Free download

PC Sun Screen will run on any PC running Windows XP or later. The software is available for download from www.thomson-software-solutions.com for £5+VAT. However, Optician readers may download the software free of charge until March 5 by using the following Discount Code: PCSSOpt15

Essential reading

There is a huge literature on this topic. Two particularly useful papers are:

• Holzman 2010 What’s in a Color? The Unique Human Health Effects of Blue Light. Environ Health Perspect 118:A22-A27. doi:10.1289/ehp.118-a22.
• Lucas RJ, Peirson SN, Berson DM, et al. Measuring and using light in the melanopsin age. Trends Neurosci, 2014 Jan;37(1):1-9. doi: 10.1016/j.tins.2013.10.004. Epub 2013.

Further reading

• 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.
• Berson DM et al. Phototransduction by retinal ganglion cells that set the circadian clock. Science, 2002; 295, 1070–1073.
• Foster RG et al. Circadian photoreception in the retinally degenerate mouse (rd/rd). J Comp Physiol, 1991; A 169, 39–50.
• Freedman MS et al. Regulation of mammalian circadian behavior by non-rod, non-cone, ocular photoreceptors. Science, 1999; 284, 502–504.
• Lucas,RJ et al. Regulation of the mammalian pineal by non- rod, non-cone, ocular photoreceptors. Science, 1999; 284, 505–507.
• Yoshimura T and Ebihara S. Spectral sensitivity of photoreceptors mediating phase-shifts of circadian rhythms in retinally degenerate CBA/J (rd/rd) and normal CBA/N (+/+) mice. J Comp Physiol, 1996; A 178, 797–802.
• Gamlin PD et al. Human and macaque pupil responses driven by melanopsin-containing retinal ganglion cells. Vision Res, 2007; 47, 946–954.
• Lockley SW et al. Short-wavelength sensitivity for the direct effects of light on alertness, vigilance, and the waking electroencephalogram in humans. Sleep, 2006; 29, 161–168.
• Cajochen C et al. High sensitivity of human melatonin, alertness, thermoregulation, and heart rate to short wavelength light. J Clin Endocrinol Metab, 2005; 90, 1311–1316.
• Revell VL et al. Alerting effects of light are sensitive to very short wavelengths. Neurosci, Lett, 2006; 399, 96–100.
• Lockley SW.et al. High sensitivity of the human circadian melatonin rhythm to resetting by short wavelength light. J Clin Endocrinol Metab, 2003 88, 4502–4505.
• Brainard GC et al. Human melatonin regulation is not mediated by the three cone photopic visual system. J Clin Endocrinol. Metab, 2001. 86, 433–436.
• Lewy AJ et al. Light suppresses melatonin secretion in humans. Science, 1980; 210, 1267–1269.
• Ruby NF et al. Role of melanopsin in circadian responses to light. Science, 2002; 298, 2211–2213.
• Rea MS et al. A model of phototransduction by the human circadian system. Brain Res. Brain Res, Rev, 2005 50, 213–228.
• Schmidt TM and Kofuji P. Functional and morphological differences among intrinsically photosensitive retinal ganglion cells. J Neurosci, 2009; 29, 476–482.
• Joshua J Gooley, Kyle Chamberlain, Kurt A Smith, et al. Exposure to Room Light before Bedtime Suppresses Melatonin Onset and Shortens Melatonin Duration in Humans, J Clin Endocrinol Metab, 2011; March; 96(3): E463–E472. Published online 2010 December 30. doi: 10.1210/jc.2010-2098
• Jeanne F Duffy, Charles A. Czeisler Effect of Light on Human Circadian Physiology. Sleep Med Clin. Author manuscript; available in PMC 2010 June 1. Published in final edited form as: Sleep Med Clin. 2009 June; 4(2): 165–177. doi: 10.1016/j.jsmc.2009.01.004
• Farhan H Zaidi, Joseph T Hull, Stuart N. Peirson, et al. Short-Wavelength Light Sensitivity of Circadian, Pupillary, and Visual Awareness in Humans Lacking an Outer Retina. Curr Biol. 2007 December 18; 17(24): 2122–2128. doi: 10.1016/j.cub.2007.11.034
• Lockley SW, Brainard GC, Czeisler CA. High sensitivity of the human circadian melatonin rhythm to resetting by short wavelength light. J Clin Endocrinol Metab, 2003; Sep;88(9):4502-5.

Effects of computers on sleep and performance

• Cajochen C1, Frey S, Anders D, et al. Evening exposure to a light-emitting diodes (LED)-backlit computer screen affects circadian physiology and cognitive performance. J Appl Physiol (1985). 2011 May;110(5):1432-8. doi: 10.1152/japplphysiol.00165.2011. Epub 2011 Mar 17.
• West KE, Jablonski MR, Warfield B, et al. Blue light from light-emitting diodes elicits a dose-dependent suppression of melatonin in humans. J Appl Physiol (1985). 2011 May;110(5):1432-8. doi: 10.1152/japplphysiol.00165.2011. Epub 2011 Mar 17.
• Cajochen C, Frey S, Anders D, et al. Evening exposure to a light-emitting diodes (LED)-backlit computer screen affects circadian physiology and cognitive performance. PLoS One. 2011 Jan 26;6(1):e16429. doi: 10.1371/journal.pone.0016429.
• Chellappa SL, Steiner R, Blattner P, et al. 10 Non-visual effects of light on melatonin, alertness and cognitive performance: can blue-enriched light keep us alert? Chronobiol Int, 2013 Oct;30(8):988-97. doi: 10.3109/07420528.2013.793196. Epub 2013 Jul 10.
• Gabel V, Maire M, Reichert CF, et al. Effects of artificial dawn and morning blue light on daytime cognitive performance, well-being, cortisol and melatonin levels. Chronobiol Int, 2014 May;31(4):496-505. doi: 10.3109/07420528.2013.872121. Epub 2014 Jan 7.
• Heath M, Sutherland C, Bartel K, et al. Does one hour of bright or short-wavelength filtered tablet screenlight have a meaningful effect on adolescents’ pre-bedtime alertness, sleep, and daytime functioning? J Adolesc Health, 2014 Oct 3. pii: S1054-139X(14)00324-3. doi: 10.1016/j.jadohealth.2014.08.002
• van der Lely S, Frey S, Garbazza C, et al. Blue Blocker Glasses as a Countermeasure for Alerting Effects of Evening Light-Emitting Diode Screen Exposure in Male Teenagers.

Professor David Thomson was Professor of Optometry and Visual Science at City University and is MD of Thomson Software Solutions