This article is the second in a series of articles where we will discuss our work over the last few years. To better understand the information in this article, we recommend that you read the first article [1].

When selecting a luminaire, you should consider the following criteria, which we regard as important for aquarium lighting.

1. The local luminaire needs a local controller with a microcomputer

In the first article, we tried to figure out precisely what you need in a multi-channel LED luminaire. It is important to create an aquarium that is visually pleasing to the individual aquarist. The luminaire can only perform this task if it has a controller that controls each color of the LEDs individually. Microcontrollers are usually used as controllers for aquarium lighting luminaires, which work with specialized software programs. This program can run either on the local computer or in the “cloud” (i.e.,  a remote computer connected to the local one via the Internet).

Before considering the options of the controller, it is necessary to note a critical feature that it should have. When buying a luminaire for an expensive system with light-sensitive corals/plants, the aquarist must ensure the tank’s inhabitants will be safe. That is, the controller should ideally provide the possibility of remote control. It is important that the aquarist has the ability to change the settings of the light if necessary from anywhere. Such a feature is also advantageous to those who maintain aquariums for their customers as they can manage their customer’s light settings remotely.

The Cloud Approach

First, let’s look at the “cloud” option. It is the easiest one for the programmer because they can use the remote computer’s almost unlimited hardware capabilities. Therefore, programs “for the cloud” are written relatively quickly and easily. But this control option has a critical disadvantage in that whenever there is an internet outage, the light cannot be operated. There are also some locations where the Internet may not be available (e.g., basements of buildings and remote/rural locations).

Light For Aquaria: Convenient Control and Error Protection

This management option also has another significant drawback. No matter how reliable cloud services are, they can fail precisely when you need them the most. Of course, it is not unreasonable for professionals to believe that cloud technology is very reliable. But even colossi such as Google suffer from global failures that make services unavailable worldwide for some time [2]! Of course, cloud technology is great because it allows the organic collection of statistical data and the possibility of remote control. But for most users, it is important to have reliable and instant control, “here and now”.

The Local Approach

Now consider another possibility where the control program is located on a local computer. This can be a desktop computer, a laptop, a tablet, or a smartphone. The main disadvantage of using a local device is that all your devices (desktop PC, laptop, tablet, smartphone) likely use different operating systems! Of course, the computer industry leader, Apple, has been working for several years to unify all these devices under a single operating system, but so far, this work is far from complete. As a result, controller software developers are forced to write multiple versions of the software, adapting it to different operating systems. As a result, the control software may look very different on different devices, which is inconvenient for the user.

Another significant problem is that the user must always check to make sure that their current device is compatible with the light unit’s software program. Also, installing the control program and ongoing software updates can be inconvenient for the user, particularly for those with little experience of using such software programs. An additional limitation is that not all locally run controllers are capable of internet remote control.


Ideally, the luminaire controller should be controlled locally, not through the cloud, and its interface should look the same on all control devices. At the same time, the control program should not require complicated installation and setup, and of importance, there should be intuitive and seamless wireless control.

Utilizing a web-based application, a controller can work with almost any modern device with a Wi-Fi connection and an Internet browser. In this instance, everything is simple – the control program must be made in the form of a website, which the user enters using a standard Wi-Fi connection and a standard Internet browser. Computers, laptops, tablets, smartphones, and smart TVs, smart refrigerators, and so on have long had such functionality. Of course, a computer is more convenient to work with than a tablet, and a tablet is more convenient than a smartphone. But if you happen to have none of the above, you can also use a smart TV.

luminaire controller should be controlled locally

Of course, this approach requires the controller to have a microcontroller and a high-powered microcomputer that will contain the site with the control program. Such controllers are often not contained within the light unit (i.e., they are separate devices) and are not cheap [3]. They also need to be safely situated in an aquarium cabinet or hood.

It is possible to make tiny controllers with high functionality that can be housed directly inside the luminaire. Look at how the microcomputer required to create such a controller looks like compared to an Intel Pentium II processor:

Pentium Processor and A Full Microcomputer

Notice the processor at the top and the full microcomputer at the bottom, which has a processor, RAM, ROM, and many other devices necessary for a computer to work, including the Linux operating system. Comparing these two devices, you can see the progress made in the last 14 years. This tiny microcomputer will have about the same speed as this larger processor for some tasks in terms of pure processor speed!

Of course, this approach to creating a controller has disadvantages as well. Writing a program for such a microcomputer is much more complicated than for the usual “big” one. Fortunately, this is only a problem for the controller’s developers, not the luminaire users. But the advantages of such a controller are not limited to those mentioned above. The presence of a microcomputer in the controller allows you to implement various functional improvements with it. Also, the use of a standard Linux operating system opens up the possibility of creating additional capabilities of the controller that the customer already owns. Such as controlling any external Wi-Fi devices – for example, pumps, maintaining power consumption counting, or even keeping a diary of observations for a given tank, which will be placed right in his luminaire.

2. Prevention of the most terrible thing – Too Much Light

There is a widespread myth among marine aquarium hobbyists that you can never have too much light. As an argument in favor of this point of view is the fact that in nature, the natural illumination in the tropics reaches more than 150 thousand lux [4]. In fact, the average daily illumination is several times less [5]. It is encouraging that recently, more and more information is emerging to show that the optimal light levels for corals are 100-150 PAR for LPS corals and 250-350 PAR for SPS corals [6]. These numbers are much less than what has thought necessary just a few years ago.

The problem is that high-powered light leads to an accelerated consumption of nutrients and trace elements, which means that the aquarium becomes unstable as a system. Some nutrients such as nitrates, phosphates, calcium, and magnesium can be monitored quite accurately with available, inexpensive test kits. But the vast majority of trace elements we cannot detect with available home test kits. Simultaneously, according to the law of the minimum [7], there are no nutrients consumed by a photosynthetic organism that does not limit its growth in its absence. In other words – If just one key element is missing, and all the others are present in sufficient quantities, this one element that is missing will stall coral growth.

This rule is easy to understand if you look at the so-called “Libich’s barrel”:

Libich’s barrel

In the example image above, it does not matter at all how long the long boards are. The shortest board will determine the water level in the barrel. Similarly, the photosynthetic organism will do well and grow well as long as the aquarium water contains all the macro and micronutrients required for its growth.

The problem is compounded because almost all aquarist novices want their corals or plants to grow as fast as possible. Then, with experience, it is realized that fast growth may not always be desirable. Furthermore, rapid growth will necessitate periodic trimming. In the case of corals, this should be done much less frequently than with plants. Shaping a bundle of plants is relatively easy. However, shaping a coral is often tricky. Therefore, sooner or later, the aquarist concludes that it is better to have slow coral growth but good coloration. However, it usually takes a long time before this conclusion is reached, during which time the aquarist may become disillusioned with the hobby.

Unfortunately, many novice aquarists try to copy experienced successful aquarists, who often use a very powerful light [8].

Too Much Light

New inexperienced aquarists who use very powerful lights often run into trouble. Photosynthetic organisms rapidly consume a particular trace element, for example, iron, manganese, and the aquarist may not replace this element,  resulting in corals that begin to stagnate, allowing algae to run rampant. In the case of a freshwater aquarium, due to the relatively high rate of biological processes (consuming all the nutrients by plants are far faster than by corals) in it, this problem is usually solved by a thoughtful aquarist. But for the marine aquarium, invasion of some parasitic dinoflagellates, such as the Ostreopsis genus [9], often leads to a complete collapse of the system. Usually, the fascination with the home saltwater aquarium ends there. This is the reason why the first year or two of the aquarium marine hobby is the most difficult.

Alongside aquarium lighting, there are two other important and related factors that should be considered -the replenishment of all necessary nutrients, i.e., macro- and microelements, and the rate of nutrient consumption.

The Replenishment of Macro & Micro Elements

Determining the depletion of trace elements is difficult as it is unique to each aquarium. In the case of freshwater aquariums, this issue has been well researched as aquarists have been keeping freshwater systems for much longer, and there are far more of them. Therefore, micronutrient supplements that satisfy most plant aquariums have become widespread. Also, protocols for keeping plants in high light conditions are widespread. There are even developed protocols for the “run-up” plant aquarium, where the young aquarium is initially under low light. As the plants begin to grow, trace element additions are adjusted to match this growth, optimizing the system. The difference in illumination for new and matured aquarium, both for marine and freshwater, can be five times or even more. But even experienced freshwater aquarists find it difficult to handle such an “overclocked” aquarium. This research will soon be shown on the YouTube channel of an experienced aquarist [10].

Unfortunately, in the case of a saltwater aquarium, the situation is not so good with trace element supplements. A few years ago, several dozen Russian-speaking aquarists teamed up to investigate the composition of widespread trace element supplements for marine aquariums [11]. All available trace element supplements were tested with the ICP test [12], totaling several dozen. This investigation revealed that none of the tested supplements had a balanced composition of elements needed for marine aquaria. Even worse, some supplement compositions were extremely illogical, and some were very similar to ordinary tap water!

Therefore, the use of supplements to compensate for trace elements in a saltwater aquarium is, in most cases, a lottery. The aquarist is forced to either periodically do an ICP test and make up for the lack of trace elements based on the test results or periodically make large water changes prepared by tested salt, which contains all the necessary trace elements in the correct proportion. In truth, the first method is quite tricky. The second does not guarantee perfect results because the trace element composition of salt can vary from batch to batch, as marine aquarium enthusiasts have repeatedly discovered.

The Rate of Nutrient Consumption

The rate of nutrient consumption depends on the temperature of the aquarium. The fact is that aquarium photosynthetic organisms can not self-regulate their body temperature, so they have the ambient temperature and the corresponding metabolic rate. A higher temperature increases their metabolic rate, their need for higher light, and the whole set of nutrients. Related to this is another widespread aquarium myth that any aquarium, whether freshwater or saltwater, needs mandatory heating. In fact, in most cases, both household freshwater and saltwater aquariums do not need additional heating.

The vast majority of corals in home aquariums are stenothermic  organisms (i.e., living within a narrow temperature range), living in nature, often at the upper limit of their temperature tolerance. Therefore, an increase in water temperature by only one °C above the long-term average maximum causes either loss of bright coloration [13] or discoloration and death [14]. The range of acceptable temperature for the vast majority of species kept in home aquariums is between 21° and 29° C. However, most corals, especially deepwater, produce the most brilliant pigments just by keeping them at 22-24 °C. Of course, at this temperature, the nutrient requirements of corals will be very low. Also, the growth rate will be very low. Consequently, the light requirements at this temperature will be close to the minimum recommended at the beginning of this section of the article. The aquarium, as a biological system, will be extremely stable in this case. As a consequence, the probability of any problems will be minimal. It is important to note that almost all fish living in a saltwater aquarium also do quite well being kept within this water temperature range (i.e., 22-24 °C).

In the case of freshwater aquarium plants, we have a greater variety of optimal temperatures. This is caused by the wider range of aquarium plants, many of which grow far away from the tropics in nature. But the same rule works for these photosynthetic organisms as well. In order to get the brightest possible coloration, they must be kept at temperatures close to the minimum for the species. Unfortunately, it is difficult for many species to obtain such a temperature in the home because, for example, some species of the genus Echinodorus can live at about 4 °C, and it is at this temperature that they have the brightest coloration.


Therefore, we have to recognize the optimum temperature, achievable in reality, which is in the range of 18-22 C. Of course, the plant’s needs in terms of  light will be relatively small at this temperature. In this case, the aquarium as a biological system will be extremely stable, and as a consequence, the probability of any problems will be minimal.

It should be noted that most species of fish living in freshwater aquariums tolerate this water temperature very well. And many of them – live much longer, are healthier, are more brightly colored, and retain fertility longer than at higher temperatures.

To summarize. The best way to build a stable and beautiful aquarium is not to accelerate the consumption of nutrients by photosynthetic organisms using higher temperatures but to provide just enough light for successful growth and maximized coloring, but no more. Of course, this approach does not eliminate the need to control the microelement composition of the aquarium water, but it gives much more time to correct the situation if a deviation occurs.

3. How much light a luminaire gives: Instantaneous, daily, and over time amount of radiation

As we have shown in a previous article [1], all photosynthetic organisms have very wide ranges of acceptable illumination, often exceeding a difference of 10 times. Simultaneously, the optimal illumination is closer to the minimum than to the maximum possible for a given photosynthetic organism.

Often the radiation of aquarium lights, especially for marine aquariums, is in the area of low visibility to the human eye. Recall that the light visibility diagram for the human eye looks like this:

light visibility diagram

The eye sees the radiation in the range 400-500 nm, which is essential radiation for corals; however, on average, the total radiation that is outputted is 20 times greater than what we see because we mainly see the yellow-green part of the spectrum. Therefore, it is not possible to estimate the amount of radiation “by eye” for typical “marine” spectra and many “freshwater” spectra, even approximately. That is why advanced aquarists believe that purchasing a PAR meter increases the probability of creating a successful aquarium by 3-4 times, or even more [6].

Quite accurate, Full Spectrum Quantum Sensors from Apogee are available today [14]. This is what one of these devices looks like:

full spectrum quantum sensor

There are also cheaper devices sold under the brand name SENEYE REEF [16]:

Seneye Reef

These devices have a noticeable error when measuring short-wave radiation, in that they have an error of about 30% of the actual radiation at a wavelength of about 400 nm. But it is possible to measure this part of the spectrum and then correct the instrument’s readings.

Since conventional light sources give a huge gradient of illumination, up to 10 times or more, it isn’t easy to correctly position photosynthetic organisms in the aquarium, even if you have a PAR meter. Even within one bundle of plants or a large coral, the illuminance can vary several times. The only possible solution to this problem is to use luminaires with true uniform illumination, which we discussed in the first article [1]. In this case, it is easier to predict the illuminance of photosynthetic organisms inside the aquarium.

Moreover, if you use such fixtures in sufficient quantity, it is possible to obtain a relatively small illumination gradient with depth. First, let’s talk about the theoretical basis of this phenomenon.

In the case of a point light source, illuminance decreases proportionally squared to the increase in the light source’s distance. If it’s a line source of light, the illuminance decreases linearly, and if it’s an infinity plane light source, it does not decrease at all, given that the environment around it is optically transparent. When you install a good number of lights with evenly distributed light, you can see this effect in real life. When the light source’s distance increases, the illuminance decreases very slow, especially if the water is transparent.

In most cases, this interesting effect allows you to place corals in more places throughout the aquarium’s surface area and depth because the light is more evenly distributed. As a result, you can place the corals that require a lot of light relatively close to the aquarium’s bottom. The long stem plants’ lower leaves will get enough light in freshwater aquariums, and their internodes become short. So the plant becomes dense and ornamental, taking on a more pleasing appearance.

This effect is almost impossible to achieve by combining light sources that do not provide uniform illumination. For example, look at the top view of the aquarium of one passionate aquarist, who tried to achieve good lighting uniformity by combining conventional LED lights:

Combining Conventional LED Lights

After installing lights that provided an even lighting distribution, his aquarium started looking like this:

even lighting distribution

And this is what the result of switching from the old set of lights to the new set of lights looks like [17]:

With New Light Set

You can see the new luminaires’ PAR values in blue and the old ones in red. As you can see, the uniformity of illumination is close to perfect, and even in the shadow area has doubled!

Unfortunately, PAR-meter measurements alone are not enough to ensure that your photosynthetic organisms are getting enough, but not excessive, light. Of course, the instantaneous luminosity that the PAR meter registers is a significant value. However, it measures just instantaneous luminosity. But photosynthetic organisms can assimilate the instantaneous illumination many times more than the optimal level. This peculiarity is especially developed in shallow photosynthetic organisms, which in nature often receive so-called Solar Glitter Lines [18].

A more critical parameter for photosynthetic organisms is the amount of light it receives during the day, called Day Light Integral, or DLI [19]. Fluctuations of instantaneous illumination in nature within a few minutes can be up to 10 times [18]! However, the DLI, in this case, changes very slightly [5].

Can we infer the DLI from our programmed lighting schedule?

Before answering this question, we would like to focus once again on the two most important points, without execution of which, it is impossible to control the amount of radiation and spectrum of the luminaire. The first we have already touched on in this article. Extremely important is a high uniformity of light and diffuse light, which the correct aquarium luminaire must provide. For a luminaire that cannot offer this, light control and DLI make little sense simply because the aquarist cannot determine, even approximately, the illuminance at a particular point in the aquarium.

The second important point is that the luminaire user must know exactly what type of LED is installed in it, that is, the exact bin of the wavelength and the amount of radiation. As we have shown here [20] even for the same type of LED, the amount of radiation depending on its bin can vary by a third. The peak wavelength of its radiation can also vary so significantly that, for example, a royal blue LED can become either almost violet or almost blue!

Unfortunately, manufacturers of aquarium luminaires rarely provide information on the set of LEDs used in their luminaires. The fact is that the careful selection of LEDs by wavelength and amount of radiation is not always possible because the required LEDs are not always available on the market. Usually, the information provided on the set of LEDs used is reduced to just stating their type, and no further information is provided at all. Below is an example of what a typical description of a set of LEDs in an aquarium luminaire looks like:

typical description of a set of LEDs

Sometimes manufacturers do not give any information about the LEDs used, showing only the appearance of the spectrum obtained by turning on all the LEDs of the lamp at full power:

showing only the appearance of the spectrum

This state of affairs is all the more surprising because for the vast majority of other technically sophisticated devices, from gadgets to cars, very detailed technical information is available. It is unlikely that you would buy a computer if the seller did not specify the RAM’s amount, right?

For comparison, this is an example of what we believe should be provided to potential customers to make an informed choice.

Ideal Spec shit of a luminaire

By clicking on the LED type highlighted in blue, the interested aquarist can download the LED manufacturer’s datasheet for more information on the LED and its amount of radiation.

Similarly, most popular aquarium luminaire controllers do not give any information about the luminaire’s amount of radiation. For example, this is how a typical interface of an aquarium LED luminaire controller looks like in spectrum forming mode:

typical interface of an aquarium LED luminaire controller looks like in spectrum forming mode

The spectrum and amount of radiation are formed by moving sliders. In this case, the user does not see the luminaire’s most critical parameters, which he controls: the spectrum of the luminaire and the amount of radiation. Combined with the fact that it is impossible to determine by eye neither the spectrum of the luminaire nor the amount of its radiation, such an interface leads to difficulties in determining the actual spectrum and the amount of radiation.

To control the luminaire logically, you must first define the basic logical units. This is quite simple. Just ask yourself the question – what do we want to control? The answer is banal – the spectrum and amount of radiation. So the controller interface needs to display both the spectrum and the amount of radiation. A good example of this shown below:

controller interface needs to display both the spectrum and the amount of radiation

Here, the luminaire spectrum is shown on the left, and above it, the amount of radiation expressed in relative units. Please find out the inscription “Total emitted power: 102%” on the screenshot. Because the manufacturer knows exactly the type of LEDs installed in the luminaire, it is also possible to indicate the amount of radiation of the luminaire in absolute units – micromoles per second. Thus, the user is accurately informed of both the spectrum and the luminaire’s amount of radiation. The spectra that the user likes can be stored in the spectra gallery.

Next, let’s move on to the formation of the daily cycle. It shows the spectra by dots, with their height indicating the amount of radiation across time. The graph might look like this:

formation of the daily cycle

Or like this:

Daily cycle another example

Other options are also possible, including the simplest, for example, when the daily cycle consists of only 4 points.

When recording the daily cycle in the gallery, the computer calculates the DLI. As a result, the gallery with these spectra looks like this:

recording the daily cycle in the gallery

The most critical parameter of the luminaire – the total amount of its radiation during the day, expressed in moles of photons, is shown clearly and very simply.

In continuation of this paradigm, long cycles look just as simple. For example, this would be what an adaptation cycle of 10 days would look like, during which each day the controller automatically gives the luminaire a new cycle, gradually moving from the first cycle with little radiation to the second one with more radiation and so forth:

long cycles

It is also possible to use another type of long cycle. Suppose a user wants to use the first variant of a daily cycle on weekdays and the second variant on weekends. In this case, the user makes such a long cycle and loops it by pressing a single screen button in the interface:

another type of long cycle

Of course, for each long cycle, the total amount of radiation emitted is also calculated, which in this case is called TGE – Total Growing Emission:

Total Growing Emission

Thus, the user has simple, logical, and quite informative control over the luminaire’s emission.

Recall the recommendations for the amount of luminaire radiation given at the beginning of this article’s second section.

Optimal illumination for corals is 100-150 PAR for LPS corals and 250-350 PAR for SPS corals. 

Furthermore, experience has shown that if the tank is not overheated, good results can be achieved with even less radiation, starting at 75 PAR for LPS corals and 200 PAR for SPS corals.

As we have already noted, DLI is the most informative and fundamental indicator. Its correlation with the instantaneous PAR value is very simple. You need to multiply the number of seconds in the daylight hours by the instantaneous PAR. Since coral habitats have a daylight period of about 12 hours with about an hour for sunrise and sunset, during which time the light hardly penetrates the water [5], it would be reasonable to mimic a similar pattern in a home aquarium. That is, we take the duration of the light day with high illumination in 10 hours. It is converting this to seconds, which equates to 10*60*60=36000 seconds. Then, we multiply PAR by 36000 and divide by a million, converting micromoles to moles, resulting in DLI. It is convenient to indicate DLI per square meter of the aquarium’s illuminated surface, which assumes uniform illumination of this area by light with a particular PAR. For example, for 100 PAR, we get DLI 36000*100/1000000=3.6 mols.

For ease of remembering, let us round up the recommended DLI. Thus, we obtain:

The recommended DLI for LPS corals is 2.5 – 5, and for SPS corals, 7 – 12 per square meter of tank surface.

The recommended DLI for plants in a freshwater tank also depends on their light requirements and is generally 2 – 3 times lower than for corals.

Recall that DLI values close to the minimum should be used for aquariums with relatively cool water and maximum values – with relatively warm water.

Of course, it is necessary to keep in mind that the recommended illuminance, and, accordingly, the DLI, is formed at a small distance from the luminaire. At some distance from it, both illuminance and DLI decrease. However, in the case of using luminaires with a uniform distribution of luminous flux, which has been repeatedly mentioned in our article, it is possible to create an unsophisticated program that will give practical advice for most photosynthetic organisms that live in home aquariums [21].

If you use luminaires with the features described in the first article and set up your daily cycles with recommended DLI, your corals will receive predictable and adequate radiation levels. Simultaneously, the likelihood of problems related to the amount of luminaire radiation will be minimized.

We hope that our articles, based on the results of our research and observations of the aquarist community, will better inform home aquarists so that more can successfully keep and grow healthy corals, which will help build a more sustainable hobby and preserve this precious wonder of the world that is sadly becoming increasingly threatened in nature [14].


  4. Christel Kasselmann “Aquarienpflanzen” (

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