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Lighting
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Light sensors are devices designed to measure light output. Considering the number
of debates that surface on message boards regarding light, it is a mystery why
more people do not own a light meter. The benefits of owning a sensor are:
1. It shows when the bulbs over your tank have color shifted and need to be replaced.
2. You can quantitatively compare different bulbs and lighting technologies. There
is no more guessing which marketing plan to believe or which Internet lighting
guru to trust. You can see for yourself numerically what you are thinking of putting
over your tank.
The two most popular probes are irradiance meters that measure light output
in terms of lux or lumens, and quantum meters that measure light in terms of
Photosynthetic Photon Flux Density (PPFD).
Irradiance meters measure the actual intensity of the light falling over a
specified area. They are generally less expensive than quantum meters, but are
also of less use for coral aquaculture. Irradiance meters focus on the total
light present, which takes into account light radiation outside of the photosynthetically
active range. This technology is better suited for use in other applications
such as photography.
Quantum meters measure the photosynthetically active portion of the visible
light spectrum. They are more expensive on the average than irradiance meters,
but are not astronomically priced. They can be purchased for roughly the same
price as a bulb replacement. An ideal quantum sensor would give equal emphasis
to all photons between 400 and 700 nm and would exclude photons above and below
these wavelengths.
Generally speaking, a light source with a PPFD reading of 100-200 is suitable
for keeping low light corals. A reading of 200-500 should be able to sustain
most corals that are found in tanks today. The most light demanding corals will
benefit from lighting in the 500-1000 PPFD range however the upper end of this
range can be extremely harmful to deeper water corals. These are very general
guidelines, and are meant to be a rule of thumb rather than a hard rule. We
still recommend acclimating corals to intense lighting schemes regardless of
how much light they are accustomed to in the wild.
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