Lighting for the human circadian clock: recent research indicates that lighting has become a public health issue
Steve Pauley MD FACS from the USA has published a very interesting (and
readble) paper on the effcts of light on humans.
The paper is availble from *http://tinyurl.com/3kaym*
Some sections of interest:
Street lighting
Residential street lighting should employ fully shielded ("full cutoff")
light to eliminate or at least minimize light trespass into homes. The
preferred high intensity discharge (HID) light source is high pressure
sodium (HPS) because of its high efficiency and long bulb life. HPS also
has lower amplitudes of blue light emission. Metal halide (MH) and
mercury vapor (MV) are less efficient and emit higher amplitudes of blue
light. Low pressure sodium (LPS) lights have the advantage of being the
most efficient i.e. LPS emits the most lumens per watt of all the
commonly used outdoor light sources. LPS emits a single wavelength of
yellow light (589 nm), and is therefore least likely to lower human
melatonin levels. LPS is also preferred by astronomers since it is
easily filtered making the imaging of celestial objects less difficult.
A disadvantage of LPS is its yellow color which is not popular with the
public, law enforcement, or emergency personnel. The very poor color
rendering index (CRI) for LPS results in red objects appearing as black.
However, the use of full cutoff LPS residential street lights may prove
to be friendlier to circadian rhythms than the typical HPS, MH, MV
drop-lens, cutoff and semi cutoff HID lamps which emit blue wavelengths.
Conclusion
Lighting only for visual acuity or to achieve decorative effects is no
longer acceptable [58
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;].
Lighting must also be friendly to the circadian clock. We must recognize
the body's need to sleep in darkness which allows for the normal night
time production of MLT. MLT is a long-evolved protective hormone that
should be allowed full expression during early morning hours.
On the basis of the growing body of animal research and human
epidemiological studies the hypothesis that exposure to LAN may in
certain circumstances harm human health should receive more attention.
More research is needed before one can definitively state that LAN harms
human health. But with the knowledge of the newly identified separate
blue light-sensitive, retinal-circadian system, the indirect
epidemiological evidence that LAN exposure to shift workers may
contribute to breast and colorectal cancers, and Blask's and colleagues'
rat–LAN–MLT–human breast and liver cancer cell research, mounting
evidence suggests precautions should now be taken with the design and
application of both indoor and outdoor lighting.
Cheers,
~Al
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