This is How Long Reef Tank Lights Should Be On!

Our reef tanks are a beautiful addition to any home or office so does that mean we just need to keep the lights on when we are there like a freshwater aquarium or do reef tanks need a different lighting schedule? 

Lights should be on for 9-12 hours every day on aquariums containing corals. Corals need light to photosynthesize and require at least 8 hours of strong light each day. Light fixtures that can dim up and down are the best way to simulate the natural lighting cycle and allow easy setting of a light cycle.

In a saltwater reef tank, light is one of the most important parts of the life support system if you plan to keep coral. Light schedules that simulate both periods of day and night are essential for establishing energy production in your coral but also simulate the natural daily cycle in the wild. During the night, fish need to sleep, the coral will feed and scavengers come out to help clean your tank.

What is the Perfect Lighting Duration for a Reef Tank?

There are many factors that go into this but it all comes down to what type of corals you have and what type of lights you have. There is an endless amount of lighting options that are available to you depending on what kind of coral you plan to have in your tank so here is a good benchmark to start with:

Have lights on for 6 hours maximum intensity – This means your lights at 100%, or all bulbs on

If your corals seem to be going brown, or the colors don’t pop, increase the light period by an hour each week. Brown coloration is a sign the coral is not getting enough light.

If your corals seem to be turning white (Bleaching), reduce the light intensity to say 75%, turn off a bulb or two on a T5 setup or reduce your max intensity lighting period to 4 hours.

These are just a starting point. Every aquarium is different but your corals will tell you. Here are some guidelines for the types of coral and lights available for your reef:

Coral Type:

  • SPS Coral & Clams – Require most intense light for the longest period
  • LPS Coral – Require less intense light, and can be for a shorter period
  • Soft Coral – Requires the least amount of light intensity & period

Light Type:

  • High Quality LED – Produce very high-intensity light. Adjustable color spectrum, timing, and dimming functions
  • Lower Quality LED – Produce moderate intensity light. Adjustable color spectrum, timing, and dimming functions
  • Metal Halide – Produce very high-intensity light. Bulb sets the color spectrum, timers to be used, no dimming function
  • T5 Fluorescent – Multiple bulbs required to get high-intensity light. Bulb colors can be mixed to provide the required color spectrum. Timers to be used. Dimming available only with the right lighting ballast and electronics.

Many reef owners will ramp up and ramp down their lights to help simulate a sunrise/sunset and to help corals get a longer lighting period but at a reduced light intensity. This cannot be done with Metal Halide lamps as they are only an on/off system.

A Typical Reef Tank Light Duration Schedule Could Look Something Like This:

Dimmable LED’s

11am – Lights turn on to 20%
12am – Intensity increases to 50%
1pm – Intensity increases to 75%
2pm – Full Intensity – 100% or All Bulbs ON
3pm – Full Intensity – 100% or All Bulbs ON
4pm – Full Intensity – 100% or All Bulbs ON
6pm – Full Intensity – 100% or All Bulbs ON
7pm – Full Intensity – 100% or All Bulbs ON
8pm – Full Intensity – 100% or All Bulbs ON
9pm – Intensity decreases to 60%
10pm – Intensity increases to 20%
11pm – All Lights OFF

Dimmable T5s

11am – Lights turn on to 20%
12am – Intensity increases to 50%
1pm – Intensity increases to 75%
2pm – Full Intensity – 100% or All Bulbs ON
3pm – Full Intensity – 100% or All Bulbs ON
4pm – Full Intensity – 100% or All Bulbs ON
6pm – Full Intensity – 100% or All Bulbs ON
7pm – Full Intensity – 100% or All Bulbs ON
8pm – Full Intensity – 100% or All Bulbs ON
9pm – Intensity decreases to 60%
10pm – Intensity increases to 20%
11pm – All Lights OFF

Metal Halide

2pm – Full Intensity – One Bulb ON
3pm – Full Intensity – All Bulbs ON
4pm – Full Intensity – All Bulbs ON
6pm – Full Intensity – All Bulbs ON
7pm – Full Intensity – All Bulbs ON
8pm – Full Intensity – All Bulbs ON
9pm – Full Intensity – All Bulbs ON
10pm – Full Intensity – One Bulb ON
11pm – All Bulbs OFF

Non Dimmable T5s

2pm – Full Intensity – Half of Bulbs ON
3pm – Full Intensity – All Bulbs ON
4pm – Full Intensity – All Bulbs ON
6pm – Full Intensity – All Bulbs ON
7pm – Full Intensity – All Bulbs ON
8pm – Full Intensity – All Bulbs ON
9pm – Full Intensity – All Bulbs ON
10pm – Full Intensity – Half of Bulbs ON
11pm – All Bulbs OFF

If your light unit is only a single bulb metal halide or the T5 fixture only has one plug, then all you can do is have the lights on at full intensity or completely off. Set the time for 6 hours and go from there. Corals going brown, increase the On time. Corals going white, reduce the On time.

A Stunning Reef Needs Good Lighting

Keeping lights constantly on is also not recommended! This will stress the fish, overexpose corals leading to bleaching and lead to unwanted algae growth. The main thing you want to achieve is to try and have the lighting schedule on for as much time as you are in the room. If the aquarium is in an office, start the lighting period at 7am, so the lights are on for your viewing pleasure while at work.

If the aquarium is at home you will want to have the lights on in the evening when you are sat relaxing. In this case, start your lights to come on early afternoon so you get the viewing pleasure. There is no point in having a beautiful reef aquarium if the lights go off when you finally get to sit and enjoy it. So long as the lighting schedule stays consistent your fish and corals will know no different. This is where timers come in!

Light Timers and Dimmers For Reef Tanks

Aquarium lighting should simulate as close as possible the behavior of natural sunlight as well as the day and night cycle.

Using timers in conjunction with lighting equipment removes the necessity of manually turning the lights on or off. A process that could be, and usually is very unreliable! There are times when you are simply too preoccupied to turn the reef tank lights on or off or there are days when you’ll simply forget altogether, then what about vacations! Successful reef tanks are all built around consistency and stability. As humans, we are hopeless at both of these!

Timers are a perfect way to ensure that the lights go on and off at the same time every day. This regulates the day/night rhythms consistently.

In the real world, the sun rises gradually and sets just as gradually. This can be somewhat simulated by dimmers. They allow for low-intensity light at the start of the reef tank’s day cycle then another low-intensity period before the start of the night cycle. 

For lights like non-dimmable T5s and Metal Halides that can only be turned on and off a timer or a series of timers used on individual or pairs of bulbs is a great way to increase or decrease light intensity as well as duration. Simple electronic plug-in timers like THIS ONE from are a cheap, but very effective way to automate your lights.

Plug-In Timer
Plug-In Timers are Perfect for Non Dimmable Reef Lights!

Dimmers are usually built into the light fixture and are configured either by a digital display, app, or online dashboard. Many dimmable T5 & LED light units can also be controlled by aquarium controllers like the Neptune Systems Apex to allow for all your aquarium equipment to be controlled from one location. These dimmable units may seem pricey but when light plays such an important part in the health of your coral, they are worth it!

The control you can get from the online and app dashboard for your lights is phenomenal! The amount of things you can do is truly mind-blowing and warrants a whole article all to itself. Sunrise, sunsets, coral acclimation programs, lightning storms, moon tracking, are all but a few of the features most dimmable LED and T5 fixtures are capable of.

How to Measure Light In a Reef Tank?

Aquarium lighting power can be measured using a PAR meter. PAR measures the amount of light intensity by using a sensor connected to a meter with a numerical readout. The higher the reading, the higher the amount of light radiation penetrating the water to that location.

As coral owners, there are two measurements of light that are of particular importance to us. The first, Light Intensity or PAR is important for how much light the corals receive, and the second is Color Spectrum.

Corals only produce energy from certain bands within the color spectrum. Ensuring there is enough light within the correct wavelengths is very important. The color spectrum also dictates what color our tank water will appear.

Light Intensity

The intensity of light is defined by a metric known as PAR. PAR stands for Photosynthetic Active Radiation. As the name implies, PAR is a metric related to the support of photosynthesis, the process that the Zooxanthellae algae in the coral tissue use to convert light to energy – Very similar to plants.

In general, aquarium lights with higher wattage have higher PAR and therefore higher light intensity.

The Various Coral Types Require Different Light Intensities to Thrive:

Soft Corals50 – 100 PAR
LPS Corals50 – 150 PAR
SPS Corals200 – 300 PAR
Clams100 – 300 PAR

The only way to truly know how much PAR your lighting system is giving out is to rent or use an aquarium PAR meter. PAR value decreases with water depth, so knowing what your PAR levels are at various depths throughout the aquarium can help you decide what corals to place where in the tank. has a 7-Day PAR meter rental which you can find HERE

Most good-quality lights designed for reef tanks will have spikes in certain wavelengths to ensure the corals get the required amount of correct PAR. Cheaper, no-name lights generally lack this and are one of the reasons why corals will not grow, even though to the naked eye the light looks nice and bright.

This is why I always recommend buying the best you can afford and buy it once. So many aquarists buy the cheap lights only to find out they don’t work and then buy the good quality lights later – Money wasted!

Color Spectrum

Color Spectrum is measured in Kelvin or K rating. This is a light metric that has to do with the ambient feel of light in the aquarium. This is also referred to as color temperature. The higher the K rating, the bluer the light. As the K rating becomes lower the light becomes distinctly warmer or yellow/white in tone. 

A good gauge for K rating would be the K rating of a noon day sun which is about 5,500K. The light of the ocean depths can be recreated by using lights with a rating of 20,000K. 

Some aquarists prefer a higher K rating for reef tanks because of the attractive ambiance of the bluish light. High K ratings also penetrate deeper into the tank allowing corals to derive more benefit from the lighting. For reef tanks the typical K range would be 6,000K to 20,000K.

Lighting Options for Reef Tanks

T5 Fluorescents

In T5 fluorescent lights an electric current reacts with mercury vapor to produce light.

A T5 Light Fixture from ATI

Bulb intensity is around 24 to 80 watts depending on its length, the longer the bulb, the higher its wattage. Each T5 bulb comes in various K ratings from a white 6,500K to the deep ocean blue of 20,000K. Actinic bulbs are also available. Actinic bulbs produce very blue light that supports photosynthesis in corals and are generally used to provide a ‘Moonlight’ style glow for late evening viewing.

Most T5 reef tank lighting fixtures come with multiple bulbs and by mix-&-matching the types of bulb color you can fine-tune the color spectrum to suit your particular taste. Most reef tank T5 fixtures also come with either full dimming capability or multiple plugs to allow pairs of bulbs to be connected to timers for individual ON/OFF control.

If you wish to find out more information on T5 fixtures or DIY kits please check out

Metal Halides

Metal halides produce light by running electricity through a compound of metals that include bromine and iodine, this metal halide compound is what gives the light its name. These are extremely high-intensity lights with typical home aquarium wattage ranging from 150 watts to 400 watts. Color temperature is obtained by the bulb/s that are inserted into the fixture. Bulbs vary from 10,000K, 14000K, and 20,000K, and bulb replacement is recommended every 12-18 months to ensure peak performance.

A Metal Halide & Reflector Light Fixture

Metal halides were the ‘Go To’ lights for decades until LED lighting technology came along. Most aquariums that run metal halide lights will require a chiller as the heat radiated into the water can increase the water temperature by several degrees while running.

Metal halides give a stunning shimmer to the aquarium and only a select few LED lights are able to replicate this. The great thing about metal halide lights is they are great for deep aquariums. The light is able to penetrate further allowing for high PAR reading on the sandbed – Great for clams!

For more information and pricing on Metal Halide systems please check out a nice selection Here at


LED stands for Light Emitting Diode. LED comes in several form factors such as tubes, rails, floodlights, or pendants. LEDs are a group of diodes arranged on a circuit board. Most reef tank LED fixtures arrange the LEDs into clusters under a single lens to help evenly spread the light to give even PAR readings across a 20″-24″ spread.

An LED Light Fixture from Ecotech Marine

Some of the best benefits to LEDs on a reef tank are that they are very energy efficient, colors and intensity can be individually controlled, they can be dimmed to simulate sunrise and sunsets and they are very low-profile units. To help penetrate deep into the aquarium many come with alternate lens covers to help focus the light a little more and by adding multiple units above the tank they can provide tremendous PAR at deep depths.

There are many great LED fixtures on the market and because of this, I created an entire article dedicated to helping you pick out the perfect LED light system for your reef tank! You can find that article here:

Best Reef Tank LED’s – Your Guide For Softies, LPS & SPS 

To Finish

For most reef tanks having the lights on between 10-12 hours will provide the maximum light for feeding your corals and for you to enjoy your aquarium. Be sure to start out at around 6-8 hours when first adding corals to your tank and see how they react. Slowly ramp up the lights ‘ON’ period or their intensity over a week or two after adding your first corals.

Whenever you buy a new coral be sure to place it on the sandbed for a few days before slowly moving up the rock work until it reaches its final placement. By doing this you allow it to slowly acclimate to your lights and prevent it from bleaching.

If you are unsure of an exact lighting schedule to follow, have a look around the forums for others with the same light fixture and use their programs as a benchmark.

Further Reading

If you found this article helpful may I suggest a few more for you:


Hi, I'm Richard and I have been an avid aquarist for over 30 years with a passion for Saltwater Aquariums. I love to pass on my knowledge to help others get the same amount a pleasure out of this hobby as I do. View my About Me page to find out more about me & my mixed reef aquarium.

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