Page 209 - Encyclopedia of Aquarium and Pond Fish, 3rd Edition

LIGHTING CONSIDERATIONS 207

SPECTRAL OUTPUT OF LIGHTS
Natural daylight is made up of a mixture of wavelengths (colors
of light)—literally all the colors of the rainbow. However, most
fluorescent tubes and light bulbs emit light at some wavelengths
in preference to others. In the marine aquarium, it is vital to select
lighting that supplies the wavelengths of light that are needed
by plants and by symbiotic algae. If you are in any doubt, consult
your aquarium dealer.
A reef tank changes in appearance between day (left)
and night (right). When lit, corals and anemones open; in Natural daylight
the dark, they close up and fish may appear duller in color.
Spectrum of light at Spectrum of light
a depth of 16 ft (5 m) at the water’s surface
The algae within corals and anemones need light at the blue
end of the visible spectrum (see box, right) to photosynthesize.
For this reason, marine aquarists tend to light their tanks
with fluorescent actinic tubes that strongly emit blue Color composition
wavelengths. Often, a more neutral daylight-simulating tube is of light at surface
used alongside the actinic tube to replicate the viewing
conditions under sunlight and eliminate any bluish cast. Color composition
of light at depth
Regular domestic (tungsten or halogen) bulbs are not suitable,
because the light quality is inappropriate, and because they
generate excessive heat, which tends to increase water
temperature and cause evaporation.
Fluorescent tubes are available in a range of lengths to 400 500 600 700
suit almost any size of tank. They have a long life span (up to Wavelength (nm)
two years), and specialized tubes are designed to deliver a Sunlight contains more or less equal proportions of all wavelengths of light. As
consistent high output throughout their life. In the case of it passes through water, red and yellow components are filtered out, which is why
reefs appear to be bathed in blue light. To set up a reef aquarium, it is essential
marine invertebrate setups, however, powerful metal halide to duplicate these lighting conditions using bulbs or fluorescent tubes (below).
bulbs may be the best option but must incorporate an Artificial light
ultraviolet filter for safety. Mercury vapor lights are another
possibility but are costly and run very hot so need to be
carefully mounted in order to disperse the heat produced.

Balanced daylight tubes give out Actinic tubes give out a predominantly
a powerful penetrating light that violet-blue light, which is required by
matches the spectrum of natural light zooxanthellae—the algae that live
for optimal viewing. symbiotically with corals.

Specialist aquarium tubes are Grow lights are used principally in
designed for power and consistency of freshwater tanks; the red-rich light
light output. They promote the growth they emit enhances the appearance
of invertebrates and algae. of many animals.

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