Advanced Guide to Planted Tank Lighting

Advanced Guide to Lighting a Planted Tank

Talking about plant aquarium lighting is really hard because of how massive this topic is. Due to its complexity, people often do not even understand what kind of lighting they need for their tanks or even what all these terms (like PAR, PUR, spectrum, watts per gallon, lumens, kelvins, etc.) mean.

I do not claim to be an expert or guru but unlike many other detailed guides to planted tank lighting on the Internet, I have tried to make complex things simple and easy to follow through (with pictures :)).

For those of you who are too impatient to read on, I can make a quick summary here. First, in absolute majority cases, we give our plants way too much light they need. Second, choose LED lights and you will not make a mistake.

Now, if you want to read everything in detail, get comfortable and let’s start. In this article, I will start from the basics and go towards more practical things.

Types of Aquarium Lighting

Nowadays there are so many options that if you are only getting into planted tanks, learning about lighting can be overwhelming and totally confusing. So, which one is better and how do you know if you have enough light for the plants?

Let’s take a look at 4 main types of lighting:

  • Incandescent
  • Fluorescent
  • Metal Halide
  • LED

Incandescent Lighting

Incandescent bulbAlthough these bulbs have been with us over 100 years, when we are talking about modern aquarium lighting, their time is long gone.

The main disadvantage of incandescent bulbs is that they are not the most efficient light source. In fact, only 5 – 10% of the energy makes light, while the rest makes heat. Therefore, there is no point in discussing them, in terms of our growing plants in our tanks.

Metal Halide Lighting

Metal Halide bulbInstead of electricity passing through a coil, these bulbs produce an arc of electricity through a halide gas at high intensity. That is why it is called a Metal Halide.

Although Metal Halides are much more efficient than an incandescent bulb, they still have lots of drawbacks:

  • They need time to warm up.
  • High maintenance (for example, Metal Halide bulbs live 5 – 10 times less than high-quality LEDs).
  • It is not uncommon to lose as much as 20% light intensity in the first 6 months alone.

Nonetheless, depending on the quality, about 25 – 45% of the energy used by Metal Halide lamps produces light. These lamps are also pretty big and it makes them a popular choice for the reef tanks. In addition, depending on the particular mix of metal halides, they can have a very high color temperature – Kelvin (I will talk about later).

Fluorescent Lighting

Fluorescent bulbFluorescent lights used to be the pinnacle of modern technology before LEDs came around. Actually, they are still easy to find and pretty popular because they come in a huge variety of sizes to fit any aquarium hood.

Fluorescents lights do not have to ‘warm up’ thanks to “instant on” technologies. In addition, Fluorescent bulbs are designed to produce light without so much heat. For example, 40 – 60 % of the electricity they use produces light. They are pretty cheap and energy-efficient. All these qualities made them a great choice for planted tanks.

LED Lighting

Light Emitting Diode bulbLED (Light Emitting Diode) is the most modern technology in aquarium lighting. It is the new guy in the town and it is rapidly replacing and making all of these other light bulbs obsolete.

LED lighting is up to 85 % more efficient than incandescent bulbs and produces significantly less heat. Even when it works for hours we can touch it without fear of getting burned that is not true for any of the types of lights. It is small, light, the most energy-efficient, so it will produce a lot of light.

Lastly, high-quality LED lights have more average rated life compared to fluorescents.

On the downside of LEDs is they are of course more expensive. However, prices decrease each year and now it is possible to buy simple LED light for low-tech tanks for relatively small money.

Without any doubt, we have a clear winner here. LEDs have surpassed all other lightbulbs in terms of efficiency. So if you are going to buy some sort of light for the planted tanks, I will definitely recommend LED lighting. However, energy efficiency is not the only thing that makes LED lights better.

Aquarium Lighting Terminology

What is Spectrum?

We can often hear that our plants need the light of a certain spectrum to thrive in our tanks. But what is the spectrum? In order to understand the concept, we need to know what the light is. Bear with me a little bit, it will make sense.

Light is the smallest quantity of energy that can be transported – a photon. Photons are elementary particles that cannot be split, only created or destroyed. They also behave like a wave, propelled by two perpendicular fields.

These waves can have different lengths. While some of them are smaller than atoms, some waves can be up to 100 000 kilometers in diameter. So when we are talking about different types of waves, we are referring to the spectrum. For example, a human eye can see photons particles between ultraviolet and infrared wavelengths.

light spectrum for aquarium plants

So, the type of wave your light is producing will determine its spectrum that can be:

  • Narrow (produces at the same time only a few types of waves, for example, only blue and red)
  • Wide (produces at the same time multiply types of waves, for example, blue, green, yellow, red, etc.)

Narrow and Wide Spectrum

So, different types of light bulbs will have different spectrums, because it depends on the way they produce light.

Aquarium Lights Spectrum Comparison

Aquarium Lights Spectrum ComparisonIf we look at the pictures, we will see that:

  • Metal Halide light has a fairly broad spectrum but it also has spikes all over the scale.
  • Fluorescent spectrum is characterized by the maximum in the blue, green and red regions.
  • LED lights produce a fair amount of lighting the blue spectrum (because they are fundamentally blue. However, we do not want to have only blue lights. Therefore, the LED-chips are coated in a phosphor that converts part of the blue light into other colors.

Note: There are also RGB (red-green-blue) LED lights, they have 3 separate chips inside one. So, they will have basically three different lights coming out and will also have 3 almost equal spikes.

What Spectrum Aquarium Plans Need

So, we have come to one of the most important parts – how does the spectrum effect aquarium plants?

All plants have special pigments that absorb photons (light) and produce their food (sugar). These pigments are called Chlorophyll A and Chlorophyll B.

photosynthesis in plants

However, in plants, these pigments also cannot use (photosynthesize) all types of waves produced by photons. Plants cannot use such waves as X-ray, gamma, etc. Like a human eye, plants are limited within a certain spectrum of waves and outside this range, plants cannot photosynthesize.

Here comes an interesting part.

According to different studies, Chlorophyll is the most efficient at absorbing red and blue light. These pigments are not great at using other types of color (such as green and yellow). The green portion of the solar spectrum is reflected not absorbed thus giving the plant its color.

Based on these results people started testing lights that produced mostly red and blue to get a better effect on plant growth. Seriously, why give our plants green or yellow lights that they do not use?!

However, all tests showed that Red and Blue lights spectrum was not as efficient as a spectrum with additional green and yellow color. Everybody was confused until recent studies showed that almost 70 –  80 % of the green and yellow spectrum also drives photosynthesis. Whereas only 20 – 30 % is reflected.

Photosynthesis is not a simple process and plants need different colors to optimize their growth. They do use all possible spectrum available to them.

Therefore, as we can see, the LED lights spectrum is best suited for planted aquarium because it provides a wide and stable range of colors. This is yet another victory for LED lights.

Planted Aquarium Lights and Spectrum. Kelvin Measurement 

We can often see in different guides that this or that plant in the tank requires 5500K or 6000K or 6500K, etc. What does it mean?

This is another term people use to describe the source (temperature) of the color. So, the spectrum of color temperatures is assigned numerical values, measured in degrees of Kelvin, noted by the symbol K.

The easiest way to remember is to imagine:

  • Candlelight. It gives off a dim glow of light that is equivalent to 1800 – 2000K
  • Sunrise/Sunset 3000 – 4000K
  • Daylight 6000 – 7000K
  • Blue sky 8000 – 10000K

The lower the K, to more red the color. To 3000K – 4000 K, the color of the light appears less yellow and more white. As we go higher on the Kelvin scale, it will progress to blue.

So, now you can ask how Kelvin measurement actually does with the growth of plants?

The answer is – It does not!

Kelvin measurement does not have any practical value for our goal. This is a very misleading term in the aquarium hobby. It can only determine the look of the tank and nothing more.

Aquarium Kelvin measurement ExamplesI will give you some examples:

  1. Kelvin rating of 3000 – 3500 will add your tank a very warm and cozy color that can be really nice if your tanks full of red plants.
  2. Kelvin rating of 6000 – 7000 is literally a white light. So if you have a tank full of green plants it will make them look very green and very lush.
  3. Kelvin rating at 8000 and higher will bring more bluish tint. This type of light is preferred in reef tanks. I believe you have seen many beautiful pictures of these tanks. Well, a lot of them are taken under 15000 – 20000 K spectrum.

Even more, it is that human eyes can see. In fact, our eyes are more sensitive to green frequencies than any other. While plants are more sensitive to red and blue, as I have said earlier. Therefore, Kelvin rating is different from the optimal spectrum of colors plants need to grow.

Planted Aquarium and Watts per Gallon Measurement 

‘Watts per Gallon’ measurement originated a long time ago when aquarists used mostly basic fluorescent bulbs that came in wattages. Nonetheless, even then a lot of hobbyists said that it was a very inaccurate way of determining the light to use for aquariums or planet tanks. They were absolutely right. This now is quite outdated for most modern lights.

Incandescent bulb vs LED lightThe problem of ‘watts per gallon’ is that:

  • Watts is a measurement of power not light! It simply tells us how much electricity is used over a set time period and nothing more. Obviously, it is absolutely useless measurement because different light bulbs have such a wide variety of efficiency.

For example, do you remember that incandescent bulbs produce only 5 – 10 % of the energy. So, a 40-watt incandescent bulb will be much dimmer than a 20-watt LED bulb because this just produces way more light.

  • Light intensity decreases exponentially over distance.

There are tall and long tanks in our hobby. So, the distance of the light to the bottom of the tank plays a huge role. The actual light intensity of the same bulb will be different at the bottom of the tanks. In long tanks, it will be much brighter.

Planted Aquarium and Lumens Measurement 

Lumen is how much visible light is the bulb giving out that we see. For example, a 40-lumen incandescent bulb and a 40-lumen LED light will produce the same amount of light, despite the fact that the incandescent bulb will consume several times more energy in terms of watts.

Incandescent bulb vs led lumenThis measurement system is a good step forward because it actually tells us how much light we are giving our plants. Unfortunately, it is not completely accurate because lumen does not solve the problem that – Light intensity decreases exponentially over distance.

Nonetheless despite its flaws, hobbyists still use lumens to figure out how much light they need for their planted tanks. After all, we do not have to be rocket scientists to have planted tanks! In most cases, we simply want to know that this light will work well enough for the plants.

Therefore, the rule of thumb says that being within a reasonable limit should be sufficient:

Lumens per liter Lumens per gallon
Low light 10 – 20 40 – 80
Medium light 20 – 40 80 – 160
High light >40 >160

Note: Keep in mind that it is the distance from the light source to the plants that matter. Although lumens cannot solve this problem, it can be still used to get a very rough estimation of whether these lights are enough for the planted tanks.

Planted Aquarium and PAR Measurement 

PAR is photosynthetically active radiation. In simple terms, PAR is how many photons are hitting a 1 square meter area or, even simpler, how much energy our plants can use in the process of photosynthesis.

Aquarium and PAR measurementPAR does not measure all the light coming from a light source (like lumen). PAR measures the amount of light that’s applied to plants. Great! You might think that this is exactly what we need for our planted tanks!

Well… there is also a small problem.

The point is that PAR meters let us measure the intensity of light but PAR does not tell us the quality of the spectrum that light produces. Of course, I can start talking about PAR meters and that they give you an average number but not the number of a certain color in the spectrum but, luckily, there is no need for that!

We already know that the spectrum of LED lights is better for planted tanks, therefore, this problem should not bother us anymore.

Below you will see the table of PAR for planted tanks. I have to say that all those numbers are the result of a general consensus that hobbyists’ derived over years of experience.

PAR for planted tanks
Low light <30
Medium light 30 – 60
High light >60

What PAR is Optimal for the Planted Tanks?

Almost everybody knows ADA Aquariums. ADA Team does an unbelievable amount of work with the gallery aquariums. Their breathtaking nature aquariums are standards of quality.

Guess what!

Some years ago, famous aquascaper and creator of the dry start method Tom Barr was there and tested PAR level of planted tanks. He discovered that every single tank had low to medium lighting in the ranges (PAR) between 30 to 50 for some tanks in the window, to 20 for some tanks in the corners.

Despite pretty relatively low levels of lighting carpeting plans (like Dwarf baby tears, Glossostigma elatinoides, Echinodorus tenellus, Cyperaceae sp, etc.) thrived.

Why?

Because aquarists often overkill when it comes to lighting requirements. We give our plants so much light that they cannot absorb all of it. In the best-case scenario, we are wasting energy and ‘losing’ PAR efficiency. In the worst-case scenario, excess of light can burn the plant or even kill it.  But how can we figure out the efficiency?

The answer is – PUR.

Planted Aquarium and PUR Measurement 

PUR is Photosynthetic Usable Radiation. Ideally, this is what we need when we are talking about growing plants or even corals.

Basically, PUR tells us how much PAR plants can absorb to grow. For example, let’s say we have 60 PAR in the tank and the plant can use only 50% (30 PAR) of this energy. It means that another 50% of this energy is wasted.

However, if we have 40 PAR in the tank, the plant will use 75 % of this energy. It means that only 25% of the energy will be wasted.

Aquarium plants. PAR and PUR measurement comparison

As you can see, PUR is more accurate reading than PAR. So, how can we measure PUR level in our tank?

Unfortunately, we have to buy a PUR meter and it is pretty expensive. The good news is that today’s LED manufacturers know about PUR. That is why their new models of LEDs often bringing in less PAR than their previous versions, and still they grow plants even better. Efficiency.

In any case, maybe with time, we will use this new measurement constantly. But for right now, PAR is the most popular way and good enough.

LED Lights Summary

To put it in a nutshell, there is almost no reason left to compare LED aquarium lights to other types of light in terms of maintenance, safety, watts, spectrum, lumens, efficiency and energy consumption, PUR and PAR, etc.

Without any hesitation, I can say that the modern generations of LED fixtures are mostly the best available aquarium light for planted tanks on the market.
Do you need to buy ultra-premium LEDs for your planted tanks?

Frankly saying, I do not think so unless you want to participate in aquascape competition or do some other crazy stuff and, what is more important, you have a clear understanding of what you are doing with your planted tank and why you are doing it.

Aquarium LED Light – Examples

Our aquarium LED light options depend on the type of tank we are planning to have – high-tech or low-tech planted tank.
Low-tech planted tank (PAR <30 at 18 inches (45 cm) from the light to the substrate) means that it is good for low-light demanding plants and that you will not use CO2.

1. Finnex Stingray Aquarium LED Light (link to Amazon)

2. Fluval Eco Bright LED Aquarium Light (link to Amazon)

3. Fluval A3998 AquaSky(link to Amazon)

High-tech planted tank (PAR 30 – 50) means that it is good for moderate to high-light demanding plants and that you will use at least CO2 and/or fertilizers. This is extremely important! Your tank must be balanced in terms of light, CO2, and nutrients. Otherwise, your tank will be covered with algae in no time.

1. Finnex FugeRay Aquarium LED Light Plus Moonlights (link to Amazon)

2. Finnex Ray2 Aquarium LED Daylight (link to Amazon)

3. Kessil A80 Tuna Sun LED Light (link to Amazon) 

There is tons of different products on the market and I cannot mention them all. I just wanted to show you some of the popular models in our hobby, so that you could have a general idea of what to expect.

Conclusion

Understanding the basics of aquarium lighting is important, especially if you are going to build a planted tank. It can save you money and frustration.

  • Plants use all the light spectrum that is visible to us (between 400 to 700 nanometers). Although green is less efficient than red and blue for photosynthesis they still need it.
  • Currently, PAR measurement is the most popular but it is about to be removed by PUR that does not care about watts, lumens, reflections, distance, and other funky stuff.
  • Many people overthink the lighting problem, they can certainly do well at 40-50 PAR at the bottom for almost any aquarium.
  • Adding so much light (as most of us used to) causes many a great deal of problems.

Research is everything. Spend a little time to understand these things especially lighting because that is probably the major factor that is going to help your plants grow.

Related articles:

Top 10 Low Light Aquarium Plants. Pros and Cons

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