From the "law of unintended consequences" department comes this finding, suggesting that the push for eco-friendly energy savings may be doing more harm to us than good.

Study links night exposure to blue light with breast and prostate cancer

LED Street Lighting
© Watts Up with That
LED street lighting with a strong blue tint.
A study performed by an international team led by the Barcelona Institute for Global Health (ISGlobal), a centre supported by the "la Caixa" Foundation, reports a link between exposure to blue light at night and higher risk of developing breast and prostate cancer. Blue light is a range of the visible light spectrum emitted by most white LEDs and many tablet and phone screens. The results have been published in Environmental Health Perspectives.
"WHO's International Agency for Research on Cancer (IARC) has classified night shift work as probably carcinogenic to humans. There is evidence pointing to an association between exposure to artificial light at night, disruption of the circadian rhythm, and breast and prostate cancers. With this study we sought to determine whether night exposure to light in cities can affect the development of these two types of cancer", explains Manolis Kogevinas, ISGlobal researcher and coordinator of the study. "We know that depending on its intensity and wave length, artificial light, particularly in the blue spectrum, can decrease melatonin production and secretion", says Martin Aubé, physics professor at CÉGEP in Sherbrooke, Canada and study co-author.
The study was conducted within the framework of the MCC-Spain project cofunded by the 'Consorcio de Investigación Biomédica en Red de Epidemiología y Salud Pública' (CIBERESP), and includes medical and epidemiological data of more than 4,000 people between 20 and 85 years of age in 11 Spanish regions. Indoor exposure to artificial light was determined through personal questionnaires, while outdoor levels of artificial light were evaluated for Madrid and Barcelona, based on nocturnal images taken by astronauts aboard the International Space Station.

Aerial image of the city of Barcelona (Spain)
© Image courtesy of the Earth Science and Remote Sensing Unit, NASA Johnson Space Center
Aerial image of the city of Barcelona (Spain) taken by astronauts of the International Space Station. many sections of the city use mercury vapor lamps (orangish) but note the sections that are blue-whitish.
Results obtained for both cities show that participants exposed to higher levels of blue light had a 1.5 and 2-fold higher risk of developing breast and prostate cancer, respectively, as compared to the less-exposed population.

Ariadna García, ISGlobal researcher and first author of the study, says: "Given the ubiquity of artificial light at night, determining whether it increases or not the risk of cancer is a public health issue". At this point, further studies should include more individual data using for instance light sensors that allow measuring indoor light levels. It would also be important to do this kind of research in young people that extensively use blue light emitting screens".
"Currently, the images taken by the astronauts on the Space Station are our only way of determining the colour of outdoor lighting at a large scale, and the spread of blue light-emitting white LEDs in our cities", comments Alejandro Sánchez de Miguel, scientist at the Astrophysics Institute in Andalucía-CSIC and Exeter University.
Reference

Garcia-Saenz A., Sánchez de Miguel A., Espinosa A., Valentín A., Aragonés N., Llorca J., Amiano P., Martín Sánchez V., Guevara M., Capelo R., Tardón A., Peiró-Pérez R., Jiménez-Moleón JJ., Roca-Barceló A., Pérez-Gómez B., Dierssen-Sotos T., Fernández-Villa T., Moreno-Iribas C., Moreno V., García-Pérez J., Castaño-Vinyals G., Pollán M., Aubé M., Kogevinas M. Evaluating the association between artificial light-at-night exposure and breast and prostate cancer risk in Spain (MCC-Spain study). April 2018. DOI:10.1289/EHP1837. Environmental Health Perspectives

The full study is here: https://ehp.niehs.nih.gov/EHP1837/

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I did some research into this.

There's a Harvard study on night light, and in particular blue light.
But we may be paying a price for basking in all that light. At night, light throws the body's biological clock-the circadian rhythm-out of whack. Sleep suffers. Worse, research shows that it may contribute to the causation of cancer, diabetes, heart disease, and obesity.

...

While light of any kind can suppress the secretion of melatonin, blue light at night does so more powerfully. Harvard researchers and their colleagues conducted an experiment comparing the effects of 6.5 hours of exposure to blue light to exposure to green light of comparable brightness. The blue light suppressed melatonin for about twice as long as the green light and shifted circadian rhythms by twice as much (3 hours vs. 1.5 hours).

In another study of blue light, researchers at the University of Toronto compared the melatonin levels of people exposed to bright indoor light who were wearing blue-light-blocking goggles to people exposed to regular dim light without wearing goggles. The fact that the levels of the hormone were about the same in the two groups strengthens the hypothesis that blue light is a potent suppressor of melatonin.

...

If blue light does have adverse health effects, then environmental concerns, and the quest for energy-efficient lighting, could be at odds with personal health. Those curlicue compact fluorescent lightbulbs and LED lights are much more energy-efficient than the old-fashioned incandescent lightbulbs we grew up with. But they also tend to produce more blue light.

See: https://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side
So it appears that a nighttime blue light component equals less sleep and therefore more stress on the body. With more stress, then susceptibility to cancer increases.

I don't know how accurate the methodologies in these studies are, but one thing is for sure, many white LED's tend to have a larger blue light component:
Light Comparison
© EE stack Exchange
Comparison of “cool white” and “warm white” LED color spectrums.
Have a look at the CREE guide to LED color mixing.
LED Color Mixing
© Cree
In cool white LED's, the two colors (blue and yellow) mix to create a white. This is shown below on the CIE 1931 color space:

Color Intensities
© Watts Up with That
The mixed color (white) will be on a line between the two components (blue and yellow). The ratio of the intensities of blue:yellow determines the final color.
Note: about 15 minutes after publication, reference to the Harvard medical study was added.