High Output Fluorescent lights

When should I change my saltwater aquarium lights

High Output Fluorescent lights 

Are you wondering: When should I change my saltwater aquarium lights? The answer, of course, is “that depends…”

How often you need to change the lights for your saltwater aquarium will depend on a few things:

1)      Whether you have a fish-only or reef aquarium

2)      How many hours you run your saltwater aquarium lights each day

3)      The type (style) of lights you have—and how hard they are run

Let’s dive a little deeper into each of these three dependencies:

Whether you have a fish-only or reef aquarium

If you have a fish-only aquarium

If you have a fish-only aquarium, then the answer to this question is easy—you change your lights when a bulb burns out, if you no longer like the look of the light, or if you begin to have issues with problem algae. If all you have are saltwater fish in your aquarium, then there is really no need to worry about when the right time is to change your aquarium lights–because nothing in your tank (besides coralline algae perhaps) depends on those lights for photosynthesis. So change them whenever they become a problem, they burn out, or you get sick of them.

If you have a reef aquarium

If you have a reef aquarium (an aquarium with photosynthetic corals or clams), then you will want to adhere to a routine schedule for changing out your aquarium bulbs–continue reading below to see how the other factors affect when you should change the light bulbs for your saltwater reef aquarium.

How many hours you run your saltwater aquarium lights each day

Every light bulb ever made is manufactured with something called a ‘useful life’. This is how long the bulb is supposed to perform regularly (remain useful). So if you consider two separate aquariums running the same light bulbs—one aquarium has the lights on 18 hours each day, but the second aquarium runs the same light bulbs only 9 hours each day—you would expect that two light bulbs with an identical expected useful life will last twice as long.

The type (style) of lights you have—and how hard they are run

Finally, the style of light you have matters considerably. LED lights generally have the longest useful lives—lasting for thousands (or tens of thousands) of hours. Metal Halide lamps generally last about a year. HO and VHO lamps last somewhere around 9-12 months, and most power compact lamps (PC) last between 6-9 months, depending on how many hours they are run each day.

What does it mean ‘how hard they are run’?

Most lights have a ballast or driver—some electronic gizmo that controls how much energy is being pumped into the light—affecting how much light comes out of the lamp/bulb. Some computerized ballasts and LED drivers are used to overdrive the lights, which squeezes more light output out of the lamp at the cost of a shorter useful life.

So how often should I change my saltwater aquarium lights? 

The best thing to do is check the packaging of your light bulb (or lamp) for the manufacturer’s listed average useful life—then divide that number by the number of hours you intend to run the light each day and mark your calendar. Short of that, consider the rule of thumb listed above if you want to be proactive and organized.

Why do you need to change your light bulbs regularly?

As light bulbs get older, the quality of the light they emit gradually degrades. You may start to notice minor differences in the coloration of your photosynthetic corals and clams—like a phenomenon called browning out (a process whereby the aesthetically pleasing ‘neon colors’ slowly fade to a less pleasing shade of brown). Even worse, old lights can be one of the confounding factors leading to a problem algae bloom or outbreak.


The decision about when to change your light bulbs is often a combination of economics (light bulbs can be expensive), aesthetics, and how many hours you run your lights and how hard they are driven by your equipment. Be watchful of small changes in the coloration of your photosynthetic corals and clams, and change them out if you begin to notice changes and have exceeded the useful life of your particular bulb. Knowing when to change your aquarium lights is as much an art as is a science, and everyone has their own opinions on when exactly is the right time to do it. I will include a few links below to some other opinions.

When to replace your aquarium lights

When should you change your aquarium bulbs

More information about aquarium lighting

Here are a few other SaltwaterAquariumBlog posts on Aquarium Lighting that you might like:

Reef Aquarium Lighting

Color Temperature Experiment

What does PAR stand for?








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