Health Effects of Artificial Light
4. What effects on health have been observed?
- 4.1 Thermal and chemical effects.
- 4.2 Effects on the eyes
- 4.3 Effects on the sleep, mood and the circacian rhythm.
4.1 Thermal and chemical effects.
Exposure to light at night can disrupt the circadian rhythm
The body has a pain reflex that makes people move away when
they feel a burning sensation so for a light source to cause
burns, it must be very intense. Lasers or high-power flash lamps
fall in this category but these are not normally used for
illumination. If parts of the skin are regularly heated, this
can lead over a long period of time to
“erythema ab igne”,
which is associated with skin
cancer. However, this is very unlikely from light
sources used for illumination.
The skin can adapt to gradually increasing levels of UV
exposure and in some people this causes tanning. However, it is
harder for the skin to respond to sudden changes in UV as when
people living in northern latitudes take a winter holiday in a
very sunny resort. Some photosensitive individuals also find
that their symptoms become worse in spring or summer if they
have not had the chance to acclimatize their skin to sunlight
during the winter months.
Overexposure to UVA and UVB causes sunburn. At first the skin
reddens and if the dose is high enough there is an
reaction causing an increase in temperature and swelling, and
after a few days the skin peels. Overexposure to UV or long term
exposure to doses of UV which are just below those needed to
cause sunburn, can aggravate
and lead to skin cancer.
People who have been sunburnt severely many times, especially in
childhood, are more likely to develop
melanoma, the most
fatal of skin cancers, as
well as squamous cell carcinomas. Over the last few decades
there has been an increase in the incidence of skin cancers,
probably because of an increase in exposure to sunlight during
holidays and leisure time.
Most of the lamps used for lighting are considered safe but
some emit UV radiation. Under extreme circumstances and over a
long period of time, exposure to these lamps could increase the
chance of developing skin
cancer in later life. The added personal risk is very
small but there could be a significant (in the hundreds of
cases) number of cancer
cases over the whole population. This added risk could be
virtually eliminated if the light was covered with plastic or
glass that absorbs UV.
4.2 Effects on the eyes
UV and IR radiation cause lesions in the
cornea and the
lens of the eye but
these can often be repaired. Long term exposure to UV from
sunlight can also cause
cataracts of the lens.
However, these types of damage are very unlikely from either
short-term or long-term exposure to lamps used for
Damage to the retina is
usually untreatable and permanent. Normal artificial lights are
not intense enough to cause burns but they can initiate chemical
reactions that proceed to harmful levels. The retina is
particularly vulnerable to short wavelength radiation such as
blue light and the susceptibility increases with age.
Natural pigments and
vitamins in the eye protect
the retina by mopping up
free radicals and
reactive species but, over time, people can develop age-related
macular degeneration (AMD), particularly if they smoke. There is
no evidence that sunlight exposure early in life may contribute
to retinal damage that would lead to AMD in later life, but
exposure to blue light could, particularly for older
4.3 Effects on the sleep, mood and the circacian rhythm.
Life on Earth has evolved around a 24-hour day with roughly 12
hours of daylight followed by 12 hours of dark; and many
biological processes follow this circadian rhythm. In mammals,
this 24-hour “clock” is controlled by the hypothalamus but is
also affected by external factors, mainly light.
Specific photoreceptors in the
information on light and send the signal directly to the
hypothalamus and to other parts of the body that influence
sleep, mood and memory.
The production of
melatonin, a powerful
hormone, is also ruled by the circadian rhythm so that it is
synthesized almost exclusively at night. This hormone sends
signals to the rest of the body to tell whether it is day or
night and promotes sleep. Melatonin also has other important
roles as an antioxidant and a protective agent against “wear and
tear” in tissues.
Exposure to light in late evening, at night or early morning
disrupts the circadian rhythm and the production of
hence has an effect on sleep, mood and cognition. Severe
disruption of circadian rhythms is linked to breast
cancer and could
also play an important role in the development of breast,
prostate, endometrial, ovary, colorectal and skin cancers;
diseases, reproduction, endometriosis, gastrointestinal
and digestive problems, diabetes, obesity, depression and sleep
Light itself has an effect on alertness, sleep, mood and the
circadian rhythms regardless of the type of lamp used. Blue
light or light enriched in blue has a more pronounced effect
than other colours or white light but lamps available to the
general population are not blue or blue-enriched.