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Actinic Light vs. Blacklight – Highlighting Fluorescent Livestock and Decor

Glo tetrasWith the growing popularity and availability of fish like GloFish and GloTetras and decorations like our own Pure Aquatic Glow Elements line, “glow-in-the-dark” and fluorescent aquariums are becoming more and more common. Most of these animals and decorations are brightly colored in any light but under special lighting, the colors will really glow. There are two main kinds of light that are used in these aquariums: “blacklights” and actinic lights. Knowing the difference between these two can play an important role in making your tank really stand out, as well as in keeping it healthy. For this blog, we will be focusing in general terms only for community aquariums. Aquarium with invertebrates and corals will have different needs since their light requirements are much more specific and extensive.

First, the science…

The colors we see around us come from the light’s wavelength, measured in Terahertz (THz) or nanometers (nm). Most people can see light ranging from about 700nm (reds) to about 400nm (purples). Blacklights and actinic lights both produce light from the bottom of the visible light spectrum (the BIV in ROY G BIV). Most actinic lighting for aquariums has a wavelength of about 420-460nm. The higher end of this range (460nm) produces a more blue color light, while the color shifts to purple approaching the lower end (420nm). This type of lighting is still well within what we are capable of seeing. “Blacklights” emit a light below what we as humans are able to see known as ultraviolet or UV light. Yes, this is the same UV light that we wear sunscreen to protect ourselves against! UV lighting is separated into three major ranges. Blacklight bulbs are UV-A bulbs (315-400nm), the spectrum which causes our skin to tan. For comparison, the UV Sterilizers popular in aquariums for eliminating algae, diseases and parasites are UV-C bulbs (200-280 nm), a destructive spectrum that is mostly filtered out by Earth’s atmosphere and the UV-B range in between is the more damaging rays from the sun that causes sunburn and other harmful conditions.

Glow ornamentRight now, some of you may be saying “But I can see when a blacklight is on….its purple!”. Not exactly. The color you see when a blacklight is on is a by-product of the UV production itself. In order for a light bulb to function, a chemical phosphor inside the glass is ignited. This produces the radiation, but it also produces visible light so a filter is used on the bulb itself to block some of this light. This filter changes the wavelength slightly so it is dampened to about 370-400nm, a range which we can start to see as a purplish or dark blue glow. Think of it like  lighting a fire to heat a room; the flame also gives off light as well as heat and you may put a screen in front of it to block the light and protect yourself from the flames. Unshielded UV bulbs are used in bug zappers to attract insects to their demise.

Now, back to your aquarium…

Making the choice between using actinic or blacklights for your glowing aquarium depends on when or how you would like to view it. Fluorescent bulbs and LED fixtures are both available with a variety of actinic and blacklight option. Both actinic lights and blacklights make things glow when the light they produce is reflected off of the fluorescent pigments in the object, whether this is light we can see (actinic) or light we can’t (blacklight). These pigments could be in the artificial coloration of an ornament or plants, or in the proteins or cells of a living creature, either artificially or naturally. Many plants and animals that we don’t think of as “glowing” have pigments that are fluorescent under the ultraviolet range. This can help them to blend in or stand out to other animals that can see this range that we can’t. Fish like GloFish have been enhanced with proteins from these fluorescent creatures at their embryotic stages so they can share in these glowing traits.

Glow Elements PlantsFor daytime viewing, an actinic light is a better choice since it produces more of a brighter light that we can see and less UV radiation that can be harmful to some more sensitive organisms in higher concentrations. Blacklights are a good option for nighttime viewing only, when you may not want to see anything in the aquarium other than those fluorescent glowing objects or fish. You may choose to use one or the other of these lights or a combination of them or more standard “white” lighting which contains a balance of the entire visible light range. Lighting an aquarium containing glowing elements with a more traditional white light or “50/50 bulb” (half white light, half actinic) during the day and changing to an actinic or blacklight at night can truly give you a dramatic change to the look of your aquarium with no more effort than the flip of a switch!


  1. avatar

    Thank you for another informative blog. Where else could I get that type of info written in such a perfect way? I’ve a project that I’m just now working on, and I’ve been on the look out for such info.

  2. avatar

    Hi, I know that black lights are harmful to turtles. Can you tell me if marine light are safe for them?

  3. avatar

    Hello Lavinia, It is my understanding that turtles do need some UVB lighting to bask but that would be a better question for our That Reptile Blog. There are lots of articles on there that can help you determine what lighting is best for the type of turtle that you have since different species will have different needs. You can view the Turtles & Tortoises category for all related articles, enter the type of turtle you have in the Search field at the top for articles about that species, or try starting with these entries about reptile lighting in general that may help you: The Season Has Changed, Should You Change Your Reptile Bulbs?, Reptile Lighting – Understanding and Using UVB Bulbs.

  4. avatar

    can ultravilot uva blue black lights work for making glowfish glow and also can a blacklight such as the one i just mentioned be visible during daytime i keep my blinds shut everyday please let me know thanks

  5. avatar

    Hi Robbie, As we discussed here, an actinic light would be a much better choice since constant exposure to an ultraviolet “blacklight” can be harmful to fish. It will cause serious health conditions over time. An actinic light can be kept on during the day as well.

About Eileen Daub

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Marine Biologist/Aquatic Husbandry Manager I was one of those kids who said "I want to be a marine biologist when I grow up!"....except then I actually became one. After a brief time at the United States Coast Guard Academy, I graduated from Coastal Carolina University in Myrtle Beach, South Carolina in 2004. Since then, I've been a marine biologist at That Fish Place - That Pet Place, along with a Fish Room supervisor, copywriter, livestock inventory controller, livestock mail-order supervisor and other duties here and there. I also spent eight seasons as a professional actress with the Pennsylvania Renaissance Faire and in other local roles. If that isn't bad enough, I'm a proud Crazy Hockey Fan (go Flyers and go Hershey Bears!).