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Aquarium Lighting - Spectrum and Lux
 THE NANOMETER RANGE (SPECTRUM)
A nanometer scale is used to measure the wave length of light energy from cosmic rays to radio
waves. An actinic bulb will have a Nanometer spike at about 420N, a UVC bulb about 265N, and a
daylight bulb about 700N. The difference in the wavelength determines how the wave affects its
surroundings. It is this wavelength difference that allows short-wave x-ray to pass through walls,
while longer-wave visible light cannot pass though the same material; short-wave ultraviolet and
x-ray can destroy DNA in living microorganisms and breakdown organic material while visible light
will not. All light energy is measured on a "nanometer" (nm) scale. Nanometer means one-billionth
of a meter.
This applies to aquariums when we consider the light spectrum and how it applies to our aquariums
individual needs: Red light is the first to be filtered out and can only penetrate a short distance. As
light waves penetrate deeper into the water, orange and yellow are lost next. Of all the colors of the
spectrum blue light penetrates the deepest. Corals need intense equatorial UVA (actinic) and even
some UVB as recent articles (and my own experience) suggest. Most plants need both actinic and
The Nanometer scale and Kelvin temperatures come together when applied to aquarium lighting this
way; Natural sunlight on a clear day registers at 5500 Kelvin degrees. Kelvin temperatures less than
5500 become more red and yellow and the higher the Kelvin temperature the more blue the light is.
Most photosynthetic invertebrates should be kept with lamps of a 20000K rating. Actinic emits a
fluorescent blue light and is usually used as supplemental lighting. Not only is actinic lighting
beneficial to photosynthetic invertebrates, it is also aesthetically pleasing to the eye when used to
supplement "daylight" lighting. Freshwater aquarium plants benefit from lighting with a Kelvin
temperature in the range of 5500 - 6500 degrees. Freshwater plants prefer light with more red and
yellow in the spectrum. What the exact Kelvin output of an aquarium bulb is takes a little faith in the
manufacturer (at least in my opinion), as it is difficult to test each manufacturers claims of Kelvin
and the application of Kelvin to aquarium bulbs takes a little bit of scientific stretching (based on the
definition of Kelvin).
A measure of the intensity of light (referred to the photometry of light), one lux is equal to one lumen
per square meter. This is important for aquarium plants. Once again this is another area of
comparing apples to apples in lights, not just watts.
This is also VERY important to most corals in marine reef aquariums. When the Lux (intensity) is not
enough the zooxanthellae (algae that are inside of corals tissues) do not create plentiful oxygen. The
minimum light intensity should be no less than 3,000-lux when it reaches the deepest part of the
aquarium. You can over light your coral to a light saturation point (quite hard in my experience, but
this should be noted), maximum Lux should be no more than 100,000 to 120,000.
By comparison Lux in tropical reefs has been measured to be between 110,000 and 120,000 Lux at
the surface of the reef and 20,000-25,000 Lux one meter below the surface.
A lux meter is an excellent investment for a serious aquarium plant or Reef hobbyist. Here are two
sites I found with these products: "Ultralife Lux Meter"; "Light Intensity (LUX) Meter"
（article by Carl Strohmeyer：Aquarium Lighting）