A recent article in Gizmodo reports:

Researchers have linked the modern form of LED street lighting to higher rates of breast and prostate cancer, in a grim development that could have repercussions for everything we look at in today's backlit world.

The implications of the study might also imply that overuse of computers or phones are also a problem:

The stats didn't cover LED light exposure from smartphone and computer use, although the researchers warn that: "We must also investigate whether night-time exposure to the blue light emitted by smartphones and tablets increases our risk of cancer. We must now improve our research methods to ensure this is robust so we can advise on how best to protect human health."

Are these credible results derived from a robust analysis? are blue lights giving us cancer?

  • I recall reading an article about this recently, perhaps in Scientific American or an IEEE publication. While I only skimmed it, the numbers are apparently derived, at least in part, from satellite observations of cities, with new satellites which can read street light colors with reasonable accuracy, combining that with cancer stats, etc. (A lot like the linked University of Exeter article.) Commented Apr 30, 2018 at 19:50
  • If a lot of UV light was emitted alongside the visible blue light I could see that increasing the risks of skin cancer. But cancers of internal organs? I see no legitimate way exposure to any electromagnetic radiation below x-rays could trigger that
    – GordonM
    Commented May 1, 2018 at 12:59

3 Answers 3


The thinking is that disrupted sleep results in lower melatonin production which through some unknown mechanism might make the body more vulnerable to the cancers.

This is classical clickbait. Even from the bit of the study that they gave, you can see that it was about the health problems of bad sleeping, caused by too much light in the night and possible health problems with using strong/cheap blue/white lights.

LEDs are just used because they are now the main source for light, especially coloured.

This topic has been going on for years now, often also involving the debate about cheap light sources, which emit "bad light"

Here an example from 1989 in this case with noble gas lighting.

In conclusion, the results are credible. You can find similar studies with similar results all over the internet. BUT the article is nonsense. It isn't about LED, in the same way the debate about industrial lighting wasn't about noble gas lights in general. It is more about overused and poorly made light sources in general.

But as you can imagine, an article with "cheap light sources can be a health hazard" or "we use too much light" don't get as much attention as "Blue LEDs (can) cause cancer".

  • Did you read the link in the link? Commented Apr 30, 2018 at 21:47
  • 1
    @DanielRHicks Did you? The research paper talks about light in the blue spectrum but it's pretty clear that it is really about increased ALAN exposure, which correlates with use of LEDs, and thus blue light. Commented May 1, 2018 at 8:22

As far as I'm aware, there is a intermediate factor which could explain it: the circadian rhythm

In the field of chronobiology, it has already been determined that light plays a major role in synchronization to the circadian cycle. For example see Duffy et al.. The article mentions the "phase response curve", which shows that certain light exposure at certain times will cause shifts in the circadian cycle. In darkness (and no other synchronization factors) the circadian rhythm will desynchronize from the wall clock time. Normal daylight helps living beings to synchronize to the circadian cycle (Experiments proving this were done in the in the 60's and before. I'm tying to find some sources). Artificial light has the potential to disrupt this natural synchronization (Nice literature study by Bedrosian)

Quite a recent discovery are the Intrinsically photosensitive retinal ganglion cells, specific cells in the eye that play a major role in synchronization of Circadian Rhythms through regulation of melanopsin (for example see Hattar et al.) It has been demonstrated that the peak sensitivity of these cells is around 470 nm, which is light blue (see for example Lucas et al.)

Disruption of the natural circadian rhythm has been related to disease (example Golombek et al.) and specifically cancer (example Shilts et al. (in mice), Davis et al. (night shift workers), Straif et al. (more shift work))

Combining the above, it seems especially blue artificial light can disrupt the circadian cycle, which is associated with increased chance of cancer.

  • This establishes that the claim is plausible, but not that it is true. Commented May 4, 2018 at 1:34
  • @BobTheAverage what claim are you referring to? The source in the OP is not making any real claims, just suggesting links and saying more research is required.
    – JHBonarius
    Commented May 4, 2018 at 10:48

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 light.

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 Station.

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.

  • 1
    Does the study merely find a correlation, or does it go on to claim causation? We expect to see more diagnoses of certain medical conditions in urban areas. We expect to see more artificial light sources in urban areas. If it is merely correlation, it is a pretty soft finding.
    – Oddthinking
    Commented May 1, 2018 at 1:46
  • @Oddthinking - From what I glean there is a correlation between cancer rates and the TYPE of artificial lighting. More LED => more cancer. And (speaking from my own understanding) the use of LED lighting isn't highly correlated with socio-economic status. Commented May 1, 2018 at 1:59
  • 1
    And is the research approach (case control study) with data based not on direct observation but on recall questionnaires good enough to detect small effects? Do people with cancer misremember their exposure so they can find something to blame?
    – matt_black
    Commented May 1, 2018 at 8:40
  • @matt_black - This is why it needs to be reproduced. Commented May 1, 2018 at 12:01

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .