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Some lights can provide broken spectrums
which mean that although it is delivering high
amounts of light in cer tain colours, it is lacking
in others.The light may still appear to be white,
but it may have serious deficiencies. PAR is
therefore a good indicator of what will work
over your aquarium.
PUR
stands for Photosynthetically Useable
Radiation.This is even more useful than PAR as
whilst PAR is what an organism
can
use, PUR is
what it actually
does
use. Unfor tunately this is
impossible to test for as it differs from species
to species. It is wor th noting though that high
PAR does not guarantee good results.
Photoinhibition
Unfor tunately it isn't quite as easy as just
putting as much light as possible over your
aquarium.There is a point at which light
becomes damaging to plants and corals in that
it actually reduces the ability to photosynthesise.
Plants can get burnt and wither and corals can
bleach. It is impor tant that you recognise this
when choosing your lighting and make sure you
don’t “overdo it”.
Light penetration
As light passes through water it loses energy
and is eventually absorbed completely.This
means that it is impor tant that the light you use
has enough energy to pass through the depth
of water for the tank you are trying to light.
Generally speaking this isn’t usually a problem
unless you have a deep tank and want to keep
animals that need high light levels at the
bottom of the tank.Ways to ensure good
penetration of light is to use very high power
lights (this method can be quite wasteful), or to
focus the light to make sure that it reaches to
where you need it.
Colour
temperature
As light is absorbed by water, it changes colour
because the longer wavelengths are absorbed
first.This is one of the reasons that deep water
can sometimes look blue.This means that
cer tain corals are adapted to a more blue-
coloured white light. Colour temperature is a
way to describe the colour of a white light. It is
based on the colour that a black body radiator
will go as it is heated to very high temperatures
and is measured in Kelvin (K), which is a unit of
temperature used in physics. So, at 3500K the
white light is yellowy – like a standard light bulb.
Natural daylight on a bright sunny day is
considered to be 6500K.The more blue-whites
that are good for keeping marine animals are at
around 10000-20000K. Rather strangely the
colours known as “warmer whites” (i.e. the
more yellowy whites) are actually cooler colour
temperatures (i.e. lower numbers).The “cool
whites” are more blue and have higher colour
temperatures. Be careful not to get confused
here!!
FACT
When changing
lighting, you should
expect a transition
period where the
plants and animals
are adjusting to the
new set up.This can
sometimes take a
few weeks.
What to consider when choosing your aquarium lights
Light is important to us
humans. It influences our
moods, our perceptions,
our energy levels.
JOHN MARSDEN