Page 8 - AquaRay

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Before the emergence of high power LEDs, the aquarist would
have had a fairly easy decision to make on whether to use metal
halide or fluorescent lighting as they each have very clear and
different advantages/disadvantages. LED lighting is now able to
outperform these technologies in most cases, but there are
still impor tant considerations to take into account.
A fluorescent tube is a low pressure mercury
vapour held in a glass tube.When a large
voltage is applied across this tube it causes
the gas to become a plasma which emits
shor t wave UV light.The glass tube has a
phosphor coating which fluoresces to
conver t the UV light to visible light.
The advantage of this technology is that
it is quite energy efficient (around 70-
100lm/W) and is available with fairly low
power consumption (usually 18-80W).
However, light is thrown in all directions
and so an inefficient reflector is needed to
direct the light into the aquarium.This
reflector will also direct heat into the water.
Over the years it has proven to be an
acceptable way to light an aquarium, however
the quality of the light is not that great as the
white light produced has a very broken spectrum.
This spectrum also degrades fur ther as the
phosphor breaks down due to the heat of the
plasma.This results in a need for regular lamp
changes which of course costs money.There is
also a safety issue with this technology as it
means having mains voltage over the tank, with
the associated risks of electric shock, and the
lamps are fragile glass and can break easily.
Broken glass in itself is dangerous, but a
breakage can also release mercury and
phosphor powder, potentially poisoning your
Practically speaking, there are lots of fittings of
varying sizes available and whilst they can be
dimmed, this requires special equipment which
is quite expensive and rarely seen in the hobby.
They can be installed in a variety of ways
including tank mounting, suspending from the
ceiling and fitting within a hood.
3 What types of lighting
are available?
There are three main types of lighting that can be used on
aquaria - fluorescent, metal halide and LED.
Occasionally another type will emerge (plasma lighting for
example) but the three types listed above are the main
staples for most aquarists