From the University of Exeter link:
A study led by the Barcelona Institute for Global Health (ISGlobal)
and involving the University of Exeter found that participants living
in large cities with heavy exposure to blue lights at night had double
the risk of prostate cancer and 1.5 times higher risk of breast
cancer. This was compared to populations with less exposure to blue
Older lighting schemes emit a glow within the “orange” spectrum, but
new modern lighting creates a bright “blue” light emission. The
researchers found the bluer the light emission that people in large
cities were exposed to, the higher the risk of cancer. The study also
found that people who lived in homes with darker rooms, by using
window shutters for example, had lower risk than those who did not.
The study, published in Environmental Health Perspectives includes
medical and epidemiological data of more than 4,000 people between 20
and 85 years of age in 11 Spanish regions. It particularly examined
Madrid and Barcelona. Indoor exposure to artificial light was
determined through personal questionnaires. In the first study of its
kind, outdoor levels of artificial light were evaluated based on
night-time images taken by astronauts aboard the International Space
As with any scientific study, the results need to be duplicated by some other groups of researchers, but there's no reason to ignore the study as "irrelevant" or "obviously not true".
But this is far from the only study suggesting this. Mathew Walker, in his book Why We Sleep, discusses the bad effects of LED lighting at some length. Some excerpts:
The light receptors in the eye that communicate "daytime" to the
suprachiassmatic nucleus are most sensitive to short-wavelength light
within the blue spectrum -- the exact sweet spot where blue LEDS are
most powerful. As a consequence, evening blue LED light has twice the
harmful impact on nighttime melatonin suppression than the warm,
yellow light of old incandescent bulbs, even when their lux
intensities are matched.
One of the earliest studies found that using an iPad -- an electronic
tablet with blue LED light -- for two hours prior to bed blocked the
otherwise rising levels of melatonin by a significant 23 percent. A
more recent report took the story several concerning steps further.
Healthy adults lived for a two-week period in a tightly-controlled
laboratory environment. The two-week period was split in half,
containing two different experimental arms that everyone passed
through: (1) five nights of reading a book on an iPad for several
hours before bed (no other iPad uses, such as email or Internet, were
allowed), and (2) five nights of reading a printed paper book for
several hours before bed, with the two conditions randomized in terms
of which the participants experienced as first or second.
Compared to reading a printed book, reading on an iPad suppressed
melatonin release by up to three hours, relative to the natural rise
in the same individuals when reading a printed book. When reading on
the iPad, their melatonin peak, and thus instruction to sleep, did not
occur until the early morning hours, rather than before midnight.
Unsurprisingly, individuals took longer to fall asleep after iPad
reading relative to print-copy reading.
But did reading on the iPad actually change sleep quantity/quality
above and beyond the timing of the melatonin? It did, in three
concerning ways. First, individuals lost significant amounts of REM
sleep following iPad reading. Second, the research subjects felt less
rested and sleepier throughout the day following iPad use at night.
Third was a lingering aftereffect, with participants suffering a
ninety-minute lag in their evening rising melatonin levels for several
days after iPad use ceased -- almost like a digital hangover effect.
Elsewhere in his book Walker discusses at considerable length how lack of sleep, and in particular, lack of REM sleep, can have a significant effect on health, including cancer rates.