Tip:
Highlight text to annotate it
X
In this nugget we will learn the basic concepts of
Light and Health.
For about 200 years, rods and cones were considered
to be the only photoreceptor cells in the eye.
Around the year 2000, medical scientists discovered
that about one per cent of our ganglion cells in the retina of the eye
are also sensitive to light.
This third type of photoreceptor cell is called
the intrinsic photosensitive Retinal Ganglion Cell,
or IPRGC.
These cells have a nerve connection to the biological clock
located in the brain (also called the suprachiasmatic nuclei,
SCN).
The SCN in turn has a nerve connection
with the pineal gland, which is responsible for
the regulation of many hormones in our body.
So there is a direct connection between light,
bodily timing and hormones.
Lighting is important for our health.
The rotation of the earth about its own axis in exactly
24 hours results in a 24-hour rhythm of light and dark.
This light-dark rhythm
regulates quite a few bodily processes.
These include the sleep-wake rhythm, the rhythm in body temperature
and heart rate, and the rhythm with which
certain hormones are produced.
These 24-hour rhythms are circadian rhythms
Because the biological clock of people is not exactly 24 hours,
we need a daily light dose to keep our body clock
in sync with the 24 hours day rhythm.
If we are healthy, our body temperature varies in the course of the day
and night by about 0.4 degrees centigrade
under the influence of the natural light-dark rhythm.
The same light-dark mechanism controls the hormones
cortisol, which is also called “energy hormone”
and melatonin, which is also called ight.
“sleep hormone” over the course of the day and night
Cortisol levels increase in the morning, then
decrease gradually but remain at a sufficiently high level
to give sufficient blood sugar (and thus
energy and alertness) over the course of the day,
falling finally to a minimum at midnight.
The level of melatonin, the sleep hormone,
drops in the morning, reducing sleepiness.
In healthy persons it then rises again
when it becomes dark to facilitate sleep
sleep (this sleep effect is strengthened because cortisol is then
at its minimum level).
The sensitivity of the recently-discovered photoreceptor cell
varies with different wavelengths of light, as does the sensitivity
of cones and rods.
The spectral non-visual biological sensitivity curve (in blue)
and the visual eye-sensitivity curve (in red)
for photopic vision V(λ),
both as a function of wavelength can be seen in this graph.
By comparing the two curves it is immediately evident
that the biological sensitivity for different wavelengths of light
is quite different from the visual sensitivity.
Where the maximum visual sensitivity lies in the yellow-green wavelength
region,
the maximum biological sensitivity
lies in the blue region of the spectrum. High-colour-temperature light
that contains more blue is thus “biologically”
more effective than low-colour-temperature light.
This phenomenon is important for the specification
and design of healthy lighting installations.
Lighting is also sometimes used as a therapy
for people with disturbances in their biological clock.
Examples are therapies for certain forms of sleep disorder,
especially in elderly, for seasonal
affective disorders, or SAD
(a form of severe winter depression),
for certain forms of eating disorders, for burnouts, and
for sleep-wake rhythm problems as often occurring
in Alzheimer patients. Disturbances in the biological clock
can also be caused by our way of living.
Examples falling in this category are jet lag
(due to long flights through many time zones).
thank you