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2
Light to illuminate
Lumens
The basic unit of light is the lumen (lm).This is a
unit of luminous flux, which is a measure of the
power of light perceived by the human eye.
Luminous flux is different to radiant flux
(measured inWatts) as it is adjusted to reflect
the varying sensitivity of the human eye to
different wavelengths of light. For our purposes
it can be thought of as the total amount of
visible light emitted from a source.The
more lumens, the brighter the light
will look.This doesn’t necessarily
mean that your tank will
look brighter though
because it doesn’t take
into account in which
direction that light
is going.
Lux
The lux (lx) is derived from the lumen and is a
measure of illuminance.This is the luminous flux
hitting a surface.This is impor tant because it is
effectively the amount of useable light. For
example 1000 lumens spread over an area 1m
2
gives you a figure of 1000 lux; however the
same amount of light spread over a 10m
2
area
gives an illuminance of only 100 lux. In shor t,
illuminance is more relevant to lighting an
aquarium than the luminous flux because this is
the measure of light that can be applied to your
aquarium.This figure will decrease the fur ther
from the light source you get, and so when
comparing different light sources the
measurements should be taken at the same
distance.
Spread
It is impor tant to get a reasonable spread of
light in your aquarium.This will allow you to
view as much as possible and to get an even
lighting effect.This can be affected by the type
of reflector or lenses used on a light.
2 What to consider
when choosing your
aquarium lights
There are two key reasons to light your aquarium
- to view the inhabitants and to suppor t life.
In this section we cover various aspects of both