It’s generally considered that artificial lighting has been a positive development for mankind. Indeed, a measure of progress in the development of a village is electrification and lighting, which these days often arrives before sewers and clean water. In cities, we’re changing our lighting systems by converting from incandescent bulbs to halogen, fluorescent and LED. The stated ambition for this is generally to make areas brighter and to cut down on electricity use. As our built environments grow and the warmth of the sun and the shade of trees is replaced with the cold shadow of concrete, more and more of us spend our days bathed in artificial light. Often, we are staring right at it: fluorescent tubes and LED arrays light the displays of our televisions, laptops and phones. What effect is this having on our physiology?
A recent study has confirmed that computers, tablets and phones can disrupt our sleep:
“The use of [light-emitting] devices before bedtime prolongs the time it takes to fall asleep, delays the circadian clock, suppresses levels of the sleep-promoting hormone melatonin, reduces the amount and delays the timing of [deep sleep], and reduces alertness the following morning.” 
If lights in the gadgets we use can effect our sleep, then what about the lights in our homes and cities? It’s all to do with type of lighting we use and the colours (wavelengths) that they produce. Previously, with incandescent lights (old style light bulbs with a wire inside) we had one colour choice: a warm light (2600K), producing wavelengths of light centred around the colour red, not that dissimilar to that emitted from a camp fire and not particularly sleep disrupting. Now however, with the phasing out of incandescent bulbs with halogen bulbs and LEDs, we’ve got a multitude of colour choices and the most readily available option is also the most sleep disruptive: cool white (4000K) and even worse, daylight white (6000k). These lights produce a more “blueish” light, much like daylight. Blue light is sleep disruptive because our eyes have special, sensitive receptors specifically for absorbing blue light. It’s been suggested that this mechanism has evolved specifically to set our sleep and wake cycles (circadian rhythm) in line with the rising and setting of the sun .
Other biological ramifications of our increasing exposure to artificial light and decreasing exposure to sunlight are yet to be considered and verified. In recognising the direction in which we’re headed - a planet where the built environment and artificial light sources are the norm - it is of utmost importance that we understand the biological effects of light, such that we can make informed decisions in our use and deployment of lighting and lit devices.
What we can do about it:
In our homes we can choose “warm white” lighting (3000k or less, look for a colour temperature number printed on the box). The lighting in our homes should not be excessively bright either.
We can turn the brightness down on our televisions, computers and phones, and even better, we can choose not to use them for extended periods at night.
On our computers we can install f.lux (https://justgetflux.com) which is free software that attempts to minimise the blue light emitted from our screens after sunset.
Councils and Governments can select “warm” lighting of appropriate intensity for our city streets. In addition to not disrupting the sleep rhythms of passers by, this will make our cities at night more appealing places to be. The phenomena of colours of light being more or less appealing at different brightness levels (daylight as opposed to night time, inside as opposed to outside) is described scientifically by the Kruithof curve: https://en.wikipedia.org/wiki/Kruithof_curve
As consumers, we can push for daylight readable, non-backlit screen technology such as the e-ink screens used in e-book readers such as the Amazon Kindle and the Pixel Qi computer display.
In dark, poorly designed office buildings where all-day lighting is required, full spectrum lighting can be fitted to mimic daylight during daylight hours.
- Ott, John Nash. 1973. Health And Light. Old Greenwich, Conn.: Devin-Adair Co.
- Beil, Laura. 2011. ‘In Eyes, A Clock Calibrated By Wavelengths Of Light’. Nytimes.Com. https://web.archive.org/web/20141030084459/http://www.nytimes.com/2011/07/05/health/05light.html?pagewanted=all&_r=0
Chang, Anne-Marie, Daniel Aeschbach, Jeanne F. Duffy, and Charles A. Czeisler. 2014. ‘Evening Use Of Light-Emitting Ereaders Negatively Affects Sleep, Circadian Timing, And Next-Morning Alertness’. Proc Natl Acad Sci USA 112 (4): 1232–1237. doi:10.1073/pnas.1418490112.
Holzman, David C. 2010. ‘What’s In A Color? The Unique Human Health Effects Of Blue Light’. Environ Health Perspect 118 (1): A22-A27. doi:10.1289/ehp.118-a22.