Actinic Lights

As far as marine aquarium lighting goes, actinic lights deserve special mention.  Marine aquarium keepers love actinics for the fluorescent glow it gives to their corals.  The pink, orange, red, blue and green colors of SPS and LPS corals simply ‘pop’ under actinics!

actinic lights

Trumpet Corals Under Actinic Lights

For many saltwater aquarium hobbyists, these intensely luminous, other-worldly colors are what drew them in to the hobby in the first place.

Sometimes referred to as ‘actinic-blue’ or ‘actinic 03’ (after the original Phillips Actinic 03 tube that started it all), the wavelength spectrum of actinic lights peaks at around 420nm (nanometers), which is the color violet in the light spectrum.  .

Actinic Lights And Coral Growth

It is importants to note that photosynthetic corals derive little benefit from actinics.  The spectrum of light produced by actinics is just not useable to corals for photosynthesis, and for this reason, actinic lights should not be used as the main light source if you are keeping corals or clams.

Actinic Lights As Supplementary Lighting

The best way to use actinics is as supplementary lighting to your main lights.

If you are using all T5 or VHO fluorescents tubes as your aquarium light source and if you are keeping photosynthetic corals or clams, it would be best to use actinic lighting in a 1:3 combination, that is three tubes of 6,500k and 14,000k and one tube of 420nm actinic.

When using actinics as a supplement for metal halide lighting, 2 or more tubes of actinic lights can be used, depending on the desired effect.

Actinic Lights For Dusk And Dawn Effects

For a ‘dawn’ effect, actinics should be the first lights on at the start of the day’s lighting schedule, before the main lights come on an hour later.  Actinic lights should remain on for the entire lighting duration.

Actinics should remain on for an hour or so after the main lights go off for a ‘dusk’ effect.  Actinic lights should then be turned off to give the aquarium at least 8 hours of darkness.

Actinic Lights | Fluorescent Tubes and LEDs

At present, 420nm actinic lights are available as fluorescent tubes in T8 NO (Normal Output), T5 HO (High Output) and VHO (Very High Output) configurations.   To add to the available choices of actinic lights, LED manufacturers are also coming out with ‘True Violet’ 420nm LEDs.

It is my experience that T8 Normal Output actinics actually provide the most intense actinic lighting! The intensity of a single T8 NO actinic bulb you will find, will bring out the most luminosity in your corals – much more than T5 High Output actinics.

This is to our advantage as we can simply use a cheap single-bulb Normal Output light fixture to supplement our main T5 HO, VHO, LED or metal halide lights.

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