Are you confused about the duration of lighting hours for your reef tank? You are not alone. Many reef aquarists, especially the beginners, get confused about how many hours of LED light they need to supply for their reef tanks.

It is recommended to ensure a photoperiod of 9 hours where 7 hours will be under the core spectrum and 1-hour of ramp-up and 1-hour of the ramp-down period. The total time can be as low as 8 hours and as high as 12 hours if required.

LED light is replacing the metal halide and T5 lights for the reef tank. But, you might not be aware that LED lights differ from them in many aspects such as the watts and lighting standard.

While we count the efficiency of the other lights with wattage per hour, we do the math differently for LEDs by determining the PAR (Photosynthetically Active Radiation).

In this article, I will share with you important tips about LED lighting hours along with other related topics regarding LED lighting in reef tanks.

Understanding Par Reading in LED Lighting

How many hours of led light for a reef tank

You can measure the fruitfulness of LED lighting with two basic measurements. You have to examine and read them immaculately to get an idea about the exact efficiency level of the LED fixtures.

The first thing you should measure is the PAR or Photosynthetically Active Radiation. PAR can be defined as the emission of light within a photosynthetic range, usually between 400 nanometers to 700 nanometers. This is the measurement of the lighting area the aquarium plants will need to prepare their food through photosynthesis. This will also help them grow.

So, how do we measure PAR? Generally, the PAR can be measured by the micromolar amount of light per square meter/per second.

Additional Read: How Much LED Light is Required For Reef Tank

Understanding the Spectrum in LED Lighting

Note that, there is no doubt that PAR plays the role of a vital measurement. But, it does not necessarily mean that it gives us a full view. It just narrates half of the story of the situation.

If you have a deeper look, you’ll discover that plants do not absorb all the quantities of the PAR scale equally. Green range (560 nanometers), for example, is absorbed by plants in a small quantity.

This is the time when comes the role of the second factor, the light spectrum. You must take the reading of the light spectrum into account along with the PAR reading to determine to what bandwidth and to what extent those most micromoles get generated.

By the way, how do you measure the spectrum? Usually, you will require a spectrometer to get the correct spectrum reading.

Importance of Understanding the PAR and Spectrum in LEDs

Measuring the PAR and Spectrum is immensely important to know how well your LED lights are performing. PAR and Spectrum together bring the whole picture of the LEDs’ effectiveness.

Long story short, PAR stands to portray the strength of the LED fixtures and the Spectrum gives an idea about how this strength works with the proper wavelength proportion to let the plants collect their food from photosynthesis.

PAR and the Spectrum help us know not only about the emitted color or wavelength from the LED lights but also about the absorption value of any specific wavelength.

When you have both the PAR and Spectrum graph at your hand, you can determine whether your light is efficient enough to supply the proper amount of light maintaining the proper wavelengths.

You should understand by now that If you want to ensure robust plant growth and correct absorption peaks for photosynthesis, you must analyze the PAR and Spectrum of your LED fixtures.

It will help you to get the PAR in the right areas (instead of the wrong ones) and at the appropriate wavelength so that the plants get the desired spectrum.

How Many Hours of LED Lighting Do You Need for a Reef Tank?

Every tank is different. The lighting period for your reef tank depends on a variety of factors such as type of corals, amounts of algae, and the position of the tank and the lighting fixtures.

Though the reef aquarists vary in their opinion about reef tank LED timing. Here I am going to give you some general recommendations about LED lighting hours.

Total Photoperiod: Total photoperiod consists of lighting with full intensity, ramp-up time, and ramp-down time. Reef aquarists differ about the total photoperiod time.

While some argue that a tank can run even if the total photoperiod is as low as 4 to 7 hours, some increase the range from 8 to 12 hours.

The total photoperiod depends on the types of corals you have in your reef tank and the PAR and spectrum that the tank is receiving.

However, I recommend you to use about 9 hours of total photoperiod. In that total time, keep 7 hours LED lights in the core spectrum with the desired PAR. Allocate the other two hours for ramp-up and ramp-down.

Core Spectrum Period: The core spectrum period indicates the amount of light with the highest intensity. The PAR also remains at a peak at this period. A core spectrum period in a reef tank should not exceed 7 to 8 hours.

Ramp-up: The ramp-up period is the length of time when the reef tank light intensity grows up from 0% to the desired core spectrum. I recommend keeping one hour of ramp-up period for the reef tank.

Ramp-down: The role of the ramp-down period is turning back the tank light from the core spectrum to dark ((0%). When it comes to the ramp-down period, I prefer it to be 1 hour.

Dark Period: Like any creature on the earth, the fishes and corals need to have some dark atmosphere around them to take rest. The dark period in the reef tank lets the corals get rid of CO2 created by the photosynthesis.

Make sure that you maintain at least 12 hours of the dark period in your reef tank.

How to Determine the Photoperiod Hours for Your Reef Tank?

To determine the exact amount of photoperiod, you have to keep the following aspects in mind.

Types of Corals: You must consider the dominated types of corals in your tank to determine the hours of LED lighting in the reef tank.

If your reef tank is dominated by SPS corals, you will need to ensure 250 to 350 PAR. On the other hand, LPS dominated tanks need only 50 to 150 PAR.

When it comes to mixed reef tanks, the PAR amount can be as low as 75 and as high as 350. And finally, the soft corals dominated tanks need only 50 to 100 PAR of light to keep the corals healthy.

PAR Amount or Light Intensity: When the PAR is high in your LED lights, you can only 6 to 8 hours of light at the high spectrum is enough for the tank. On the contrary, low PAR and low with medium or low spectrum will require more hours of lighting.

In case you have high-intensity lighting, that will fit best with LPS and SPS corals whereas low-intensity lighting is ideal for soft corals.

Light Colors: The colors of your LED lights are also important to determine the LED lighting hours. Softies or blue lights use the lowest intensity. Those can be used for the longest period without causing any negative impacts on the corals.

You can use red and green lights moderately at an equal proportion.

And when it comes to using the white lights, you have to be the most careful. It is because if you use them for a longer period than necessary, they might cause coral bleaching. It is best if you can limit the white light intensity within 50% at the beginning.

Position of the Fixtures: The position of LED fixtures affects the water temperature and that’s why it is an important parameter to define the LED lighting hours. If the LEDs are fixed at a lower position, the water will have much temperature and PAR out of them.

On the contrary, if the LEDs are in a raised position, the water will take time to consume the temperature and the PAR.

So, if you place the LEDs at a higher position, you will need to ensure more hours of light. On the other hand, LEDs at the lower position might require 1 or 2 fewer hours of light a day to keep the corals and fishes healthy.

How to Program the LEDs for your Reef Tank?

When it comes to using T-5 or metal halide lights, you just need to think about the duration and intensity of running the lights.

However, times have changed and in case you move to LEDs, you have to think about how you can program the multiple channels of lights that come with different colors.

You also need to figure out the length of time, brightness, PAR, spectrum, and the right color while you set LEDs for a modern reef tank.

We can make three groups to categorize the type of LED lights we need:

  1. Blue (including UV)
  2. Red and green.
  3. Warm white and white.

Let me explain how to program these three types of lights in your reef tank.

How to Program the Blue LEDs for Reef Tank

Using lights of the blue spectrum can be viewed as the foundation of coral lighting. But, you might find it difficult to enlighten all the corals with blue lights only. You can ramp them up from zero to the fullest in one hour or two. However, you can keep the tank under these lights for 8 to 10 hours.

You might just try to use blue lights for corals avoiding other lights. But, though it is good to start with the blue and corals might be okay with it, only the blue spectrum can’t help the corals grow and flourish.

How to Program the Red and Green LEDs for Reef Tank

I consider the red and green as accessory colors. If you are a beginner, programing the red and green in combination with other colors of light might seem confusing to you.

Our first recommendation for programming the red and green light for your reef tank is using both the color in equal proportion.

Keep in mind that excess red light might attract more nuisance algae in your tank. Moreover, deep corals like Stylocoeniella and Leptoseris do not like to get under excess red lights for too long. So, refrain from using unnecessary red lights in the reef tank.

Use them in a way so that they are bright enough to get noticed and that’s enough.

How to Program the Warm White and Warm LEDs for Reef Tank

White LEDs are incredibly bright and offer more PAR than other light types mentioned above. Sometimes they can be so bright and powerful that corals strive to get used to them.

To avoid coral bleaching, I recommend you use bright white lights for half of the time of the photoperiod. On top of that, you should not use white lights with more than 50% intensity.

If you can manage a PAR meter, make sure that the lights do not exceed 400 umols (micromole) light for longer than 6 hours.

To avoid any harm to your corals due to overlighting, it will be wise to keep the bright light corals at the top and low light corals at the bottom of your reef tank.

Are There Any LEDs Specifically Designed for Reef Tanks?

There are not many manufacturers out there who have ventured to make specialized LEDs for reef tank use.

The case is that there are many LEDs available to use for different purposes. They come with specific properties like CCT and CRI.

However, it is not impossible to use them for your reef tank if you know how to acclimate the tank inhabitants with the PAR and spectrum of the LED lights.

When I am writing this, LED bulbs of 8000k are available for reef tanks. But as the manufacturers are trying their best, we can expect to get LEDs with a higher power soon.

Pros and Cons of Using LEDs for Reef Tank


“Why should I replace my T5 or fluorescent with LEDs in my reef tank”? Is it the question that pops-up in your mind? Well, the reasons for moving to LEDs are many.

  1. Most of the people love the long life of the LED bulbs along with the low wattage. You will find some manufacturers who are even selling their LEDs with a claim that those will last up to 50,000 hours. Long service duration is a unique selling point of LED fixtures.While a T-5 light will last for 1 year, a good-quality LED can last as long as 11 years if you use them for 12 hours daily.
  2. Another reason why LED lights will be a better alternative is low energy consumption.  Though the price of LEDs might discourage you to buy, the energy-saving efficiency of them is extraordinary. You will pay less when it comes to electricity bills.
  3. Next comes the amount of heat LEDs produce. Keeping the tank water temperature normal is tough with T5 and fluorescent as they produce much heat.But, with LEDs, you will experience something different. LEDs produce a very low amount of heat that keeps the tank much more liveable for inhabitants. Many reef aquarists just love to talk about the shimmering effect LEDs create.
  4. LEDs can help you control the growth of nuisance algae in the reef tank. Many LED users have reported that they have experienced an immediate reduction in nuisance algae when they have turned to LED fixtures.


So, do LED lights come without any drawbacks? The answer is, no. Let’s see two disadvantages of using LEDs for reef tanks.

  1. Setting an LED fixture for the reef tank is costly. You have to add more money with the cost of T-5 and fluorescent lights to get LEDs in your reef tank. However, the fact of the matter is you do not need to replace them as frequently as you would replace your T-5 and fluorescents.
  2. As most of the LEDs come with increased PAR and light intensity, it might be somewhat difficult, especially for hard corals, to acclimate with the changed intensity.

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