Page 6 - AquaRay

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4
Light to suppor t life
Always refer to your local fish stockist with regards to the
requirements of your par ticular species
Wavelength and
spectrum
Visible light is actually a form of electromagnetic
radiation that our eyes are sensitive to.This
means that it can be thought of as waves of
energy radiating through space.The length of
one of those waves defines the colour of the
light and for visible light it is measured in
hundreds of nano meters (nm). For example
violet radiation is about 410nm-440nm,
then comes blue at 440-460nm.This
continues through all colours of the
rainbow until we get to red at around
700nm.When these wavelengths are
combined, different colours can be made
– for example 450nm (blue) and 700nm
(red) would look like purple light to us.
When most of the colours are represented
in fairly balanced amounts (par ticularly red,
blue and green), then the human eye will see it
as white light.The amount of each colour in a
light is called its spectrum (see example).
A good spectrum will be as close to natural
sunlight as possible which means there will be
light present from every wavelength throughout
the visible spectrum.
PAR/PUR
Photosynthesis is a process that both plants and
most corals use to turn light into food.This
process allows these organisms to grow and
flourish and, without this light, they would die.
PAR
(Photosynthically Active Radiation) is the
measure of light within the range of
wavelengths used by photosynthetic organisms
(400-700 nanometers). It is measured in
microEinsteins/m
2
/second. In physics, light is
thought of as par ticles of energy, or photons.
An Einstein is one mole of photons, where a
mole is the number of carbon atoms in 12g of
carbon (6.0221415×10
23
).
Like illuminance, PAR measurements will
decrease the fur ther from the source you get,
and so when comparing different lights the
measurements should be taken at the same
distance.
So, PAR is basically a measure of the amount of
light that photosynthetic organisms can use, and
photosynthetic organisms include the plants
and corals in your aquarium.This makes it an
impor tant factor in choosing your lights. If you
are keeping cer tain species that require a lot of
light then you need high PAR levels.This doesn’t
necessarily mean getting the brightest light you
can, because the quality of the spectrum of light
is impor tant.
Example colour spectrum