Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (2023)

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (1)

The tank below uses a custom build BML LED bar on this tank. You can see the mix of Red, Blue and Warm white LEDs mixed with neutral white LEDs being used. The fixture gives a long height clearance above the tank, which enables pruning work without the need to move the lights - to achieve this the LED bar uses a narrow 45 degrees lens. The light bar is 34 inches away from the tank floor, and yet we can grow demanding carpeting plants in the scape. With the right knowledge we can customize our fixtures to suit our aquascaping needs. In this particular setup, it is not that the light is super high powered (though it is very efficient at only 75 watts), it is that it uses narrow angled lens (25 degrees) to focus the light produced onto the floor area of the tank. The light will not work mounted lower as it will then not cover the whole tank.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (2)

The right aquarium light affects everything: it can increase aquarium plant coloration, determine growth rates, and impact algae control. We need to determine suitable strength as well as ​colour spectrum, and cut through the science jargon that tends to be thrown around liberally here.

No other topic is filled with as much misinformation and marketing gimmickry as aquarium lighting, for example the idea that 6500K is an "ideal" spectrum - my light above is rated at 3600K, far different from a plain 6500K light and we have grown tanks with 12000K lights as well. K rating is no indicator of whether a light is suitable to grow plants or not. It simply measures the visual color hue of the light. However, light manufacturers will claim that 6500k is like daylight and assign tags such as 'full spectrum' to the light. Neither of those points are actually important in choosing a light.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (3)

A mix of tanks grown using different K rating lights.

"Full spectrum" is similarly a marketing term that has no bearing on how well a light grows plants. Any white light can be labeled full spectrum as all white light contain RGB (red, green, blue) wavelengths of light by default. More over, one can also grow plants just as easily without full spectrum light. The international space station uses just red & blue LED diodes to grow plants for example.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (4)

Even many biology textbooks have also yet been updated to reflect new data in this area; for example, that plants are found to use a significant amount of green light for photosynthesis.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (5)

So what actually matters? 3 important factors to grade a light unit

Strength

Spectrum

Spread

Factor1: Strength - measured in umols of PAR

PAR (Photosynthetically Active Radiation) is the most accurate gauge of a light's relevant 'strength' for plant growth as ​it directly measures the amount of light available for plant photosynthesis. PAR numbers are given by most esteemed light manufacturers. Go hereon how to read manufacturer's PAR tables. If PAR readings are not given by the light manufacturer, you can often find readings taken by hobbyists who own PAR meters.

What if no PAR tables or hobbyist data is available? The other way to gauge whether a light will grow the plants you want is to see tanks that are running that particular light. If other hobbyists using the same light can grow the same plants you want to grow, chances are it'll work.

(Video) Planted Aquarium Light. Plants 101 Lighting

Why Lumens and watts are poor indicators for light strength

Lumens is what some outdated websites use, however, it is a poor measurement as it measures light brightness with respect to human eye sensitives to the electromagnetic light spectrum. This means that lights that are heavy in green wavelengths have a higher lumen value as human eyes are more sensitive to green than red or blue. Plants however, use red and blue light efficiently for photosynthesis, so red/blue heavy lighting may have low lumen values but can be really great for growing plants. Similarly watts per gallon, was the old rule used when fluorescent lighting for aquariums was the norm. However, watts measure how much electricity a light unit consumes - not how much it outputs. An inefficient light may have very high wattage, but channel a lot of the energy in inefficient heat rather than light energy. The tank at the top of the page uses a 75 watt LED light on a 65 gallon tank (1.2 watts/gallon) - despite being mounted 16 inches from the tank's rim, it still produces enough light to grow colored plants well because of the efficiency and lens of the LEDs use.

The farm tank below uses T5 tubes; (39w x 8 tubes = 312watts). Over a 46 gallon tank, it comes in at 6.8 watts per gallon. This is a huge difference from the LED system used in the top tank.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (6)

How much PAR should a tank have?

The light should produce sufficient PAR at the substrate depth of your tank. The broadguidelines as commonly used by the aquatic plant community is as follows :

PAR ValuesSuitable for
20 to 30 umols

Low lighting - suitable for shade aquarium plants such asAnubias, Java fern, Cryptocoryne and mosses. If you are growing these, using low lighting just makes life easier - less algae issues to deal with. Less light means slower growth rates and less maintenance overall.

~50 umols

Medium Lighting. With good CO2, you can grow any commercially available plant, but may not get the most intense coloration in colored plants. Good for carpets. Most carpets grow denser with at least medium levels of lighting.

90+ umols

High lighting - Good for red/colored aquarium plants. Higher lighting will bring out coloration more strongly. Allows for greater density and self-shading effects. However, this level of lighting requires good control of tank cleanliness and plant health to avoid algae issues.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (7)

Using a PAR meter shows that this tank has 128 umols of PAR at that point on the substrate. Areas that are shaded will measure lower values. Light manufacturers often publish PAR tables to show how much light is produced by a light unit at a certain water depth. Alternatively, many hobbyists own PAR meters and take their own readings.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (8)

How muchPAR will you get if you squeeze 8 X 39w T5 tubes onto a 90x45x45 cm tank ? Around 200+ going by PAR meter measurements. Extrapolating from this; most 90x45x45cm tanks will grow well with half the number of T5 tubes that we are using, 4 x 39w will be expected to give around 100+ umols of PAR.

(Video) 5 Things I Wish I Knew About Planted Aquarium Lighting

This article explains how to read PAR tables by different manufacturers

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (9)

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (10)

A 4 tube T5 unit over a 2 feet tank is cheap and still produces a lot of light.

Downside of strong lighting?

The main downside of having too much light is increased chances of triggering algae growth. This sounds trivial but managing algae is probably the biggest challenge for beginners in this hobby, so it is smart to use weaker lighting if you keep only shade plants.

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Using very strong lighting without good tank fundamentals trigger spectacular algae blooms. That being said, if a tank is run on poor fundamentals, using low lighting doesn't guarantee an algae free tank - algae just grows more slowly. The important thing to remember when facing algae is removing the potential triggers. Even tanks at 100+++ Umols of PAR at the substrate can be kept perfectly algae free if it is clean of organic waste and plant mass is healthy. More details on the algae page.

That being said, stronger lighting, coupled with good fertilisation/CO2 brings out richer colours in coloured plants.

Factor2: Colour spectrum

The goal is a balanced spectrum with emphasis on the red and blues. The accurate way to is to look at the spectrum graph itself - if available. The K rating is only a loose proxy.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (12)

Which spectrum works best? Heavier reds/blues improve contrast of fish and plants

(Video) Planted Tank 101: LIGHTS - The Best Aquarium Lighting

While aquarium plants use all colours of the spectrum for photosynthesis, we find it advantageous to have stronger reds/blue in a fixture as it gives better colour contrast for the colours commonly seen in aquariums. Having stronger red/blue spectrum also stimulates coloration in red/coloured plants. We will never use an LED fixture with just plain white LEDs due to the lacking spectrum of plain diodes.

Ultimately the main deciding factor is that the spectrum has to look visually good to the tank owner. Aquariums are visual art, and aesthetic color rendering is essential. A basic way to choose a light is to copy the light choices of tanks that you like. You can do this by browsing tank pictures on the internet, but due to the issues of photography this may not be as accurate as seeing the light over a tank in person.

The K rating of a light gives the approximate colour hue of the light but doesn't tell whether the light has a good spectrum distribution or not.

Read more here on what K rating measures.

Reading Spectrum Charts

Most serious light manufacturers will publish spectrum charts for their light units. Below shows the spectrum chart of a BML LED light unit and my tank under the light. The amount of each color light being produced is equivalent to the area under the curve. This particularly light unit has large spikes in blue and red, and produce little yellow and cyan light. This spectrum profile highlight reds and blues in the tank.

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What is important is the relative area/size of peaks. To appear neutral white light, a light will have spikes in blue, green and red. A light that is all blue and red, with no green will appear pink/purple and cast a reddish hue over the tank. In this way, we can roughly gauge the overall colour rendering tone of the light by reading the spectrum chart.

Does a higher CRI rating on the light matter? In short, it does not. For most aquarium hobbyists, color accuracy is not as important as color saturation. CRI measures color accuracy of light units whereas hobbyist over overwhelmingly prefer lights that have high color saturation and contrast. Again referring to the tank at the top of this page; it's CRI rating is only 78, however, it gives good color saturation and contrast for viewing.

This article explains how the CRI is actually calculated, and why it does not really matter.

Higher amount of red/blue gives better color contrast and better pigmentation in plants

(Video) Aquarium Lighting 101 | LED Light Specs Explained

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (14)

Higher percentage of Red/Blue in lights grows plants with better pigmentation (stronger colors) and also gives better visual contrast & saturation. This tank is grow using the T5 arrangement below with a mix of red/blue and orange bulbs.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (15)

Read more here on what light spectrum planted aquariums should aim for

Factor3: SPREAD

Here, the important thing is that the fixture spread must match tank dimensions. We have found thatdual LED fixtures or a T5 array serves complex hardscapes that have shaded areas, as having two or more light sources will tend to reach most areas of the planted tank. A setup with poor spread (e.g. single bulb) will have very high PAR values in certain areas (often the centre of the light) while the edges are shadowed.

Point sources have circular areas of coverage and are best suited for square planted aquarium or tank dimensions that can be divided into squares with minimal overlap. Aquascaping rocks and other tall hardscape easily block the light from point sources from getting to plants. Using 2 fixtures, front/back or going for lighting sets that come in an array may work better.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (16)

A wide angled LED light bar has a dispersion pattern where higher pieces of hard scape can block light from reaching plants behind the hardscape. Object simulated by blue block in the diagram.

Planted Tank Lighting 101: Understanding the basics of planted aquarium lights (17)

A more distributed light source; such as a wider LED array or T5 array will not face a similar issue.

Here are links to further reading:

1. Algae control

2. How to read PAR tables

(Video) Best Planted Aquarium Lights Buying Guide - Top 7 Review [2022]

3. What light spectrum do plants use for photosynthesis

4. What does the K in 6500K actually measure

5. What light spectrum work best for planted aquarium light fixtures

FAQs

What should I look for in a planted aquarium light? ›

A soft, warm reading light that gives everything a yellowish glow may have a rating of 2700K, whereas a cool white light with a bluish tint may be labeled as 10,000K. To be honest, color spectrum doesn't matter that much when it comes to growing aquarium plants because they can thrive under a wide range of Kelvin.

What color light is best for plant growth in aquarium? ›

Colors of Light for Healthy Growth of Aquatic Plants

Red and blue lights are used in photosynthesis of plants. Red light is attenuated rapidly in water while blue light has better penetration in water.

How many watts of light do I need for a planted tank? ›

A good basic rule to follow is to provide 1 to 2 watts of lighting per gallon for fish-only aquariums, 2 to 5 watts per gallon for freshwater planted aquariums, and 4 to 8 watts per gallon for reef aquariums.

How long should I have my lights on planted tank? ›

How long should I keep my aquarium lights on? To provide animals and plants the lighting they need, 10 to 12 hours a day is sufficient. Installing a timer or purchasing a unit with integrated timing can make lighting easier––just set it and forget it. Keep in mind algae loves light as well.

How do I know if my aquarium plants have too much light? ›

Signs Of Too Much Light On Aquarium Plants And Its Effects
  1. 0.1 1. Overgrown Leaves.
  2. 0.2 2. Leaves Changing Color.
  3. 0.3 3. Brown Edges On Leaves.
  4. 0.4 4. Algae.
  5. 0.5 5. Rotting Leaves.
29 Jul 2022

What color light is calming for fish? ›

Blue lights are great for your aquarium plants. They're also exceptional for your fish because of the calming effect of blue.

What does blue light do to aquarium plants? ›

Blue light is good for aquarium plants as it is the most important part of the light spectrum for driving photosynthesis. Plants grown under blue light abundantly will have strong and healthy leaves and stems. Also, blue light enhances the color of aquatic plants which helps aquarium to look more rich and vibrant.

Can I leave blue light on in fish tank? ›

No, you should not keep a blue light or any other colored light on in your fish tank through the night. Unless you have nocturnal fish, they depend on light cycles to maintain their sleep cycle. Leaving a light on at night will disturb this cycle and result in sleep-deprived and stressed fish.

Do aquarium plants need red light? ›

Can You Use Grow Lights For Aquarium Plants? Whether grow lights can be used in planted aquariums is a really tricky question to give a straight answer to. Even so, it a well-known fact that all plants need light to grow, including aquatic species. Aquarium plants do exceptionally well with red, blue, and green light.

How many LED watts per gallon planted tank? ›

How much watt LED is needed for the planted tank? In general, you need about 1-5 watts per gallon to light a planted tank.

Do blue LED lights cause algae? ›

Contrary to what you may have been told, LED lights do not cause algae growth any more than other aquarium lighting options.

Is 6500K good for aquarium plants? ›

Every website out there that claims 6500K is better for plants is purely a marketing gimmick. For aquarist purposes, K rating is useful when buying household lighting and re-purposing it for aquarium use.

Is blue light good for aquarium plants at night? ›

Blue light bulbs promote aquarium plant growth. They are also compatible with the fish species, preventing them from harming them. The moonlight bulbs or the blue light bulbs are perfect for the skittish fish species and keep them calm during the night.

How high should my aquarium lights be? ›

How high do I need to mount my Aquaillumination lights above the water? Answer: To achive the best light spread and to help prevent water spashing on the lights we recommend the bottom of the units are between 12" (31cm) and 15" (38cm) from the surface of the water.

Can I leave my aquarium light on 24 7? ›

You should never keep your aquarium lights on for 24/7. There are are several reasons you should not do so but the most important is it will cause algae growth in your tank. And you can spend literally weeks if not months to clean out algae from your aquarium. Besides, just as we do fish also require darkness to sleep.

How do I know if my aquarium plants are healthy? ›

If your plants are turning yellow, another possibility is that the plants in your tank are not receiving enough nutrients to facilitate healthy growth.
...
DIAGNOSING PROBLEMS WITH AQUARIUM PLANTS.
Symptoms ExhibitedLikely Cause
Leaves turning yellow or redNitrogen deficiency
Leaves turning brown/black, plants dyingExcess phosphate
5 more rows
24 May 2022

Can Too Much light cause brown algae? ›

Not only can too much light cause you problems, but too little light can also lead to excessive algae (in particular, brown algae). Therefore, it is not generally a good idea to simply stop turning your light on to get rid of the algae.

Can there be too much light in planted tank? ›

Yes there is such a thing as too much light. Using an intense led flood light with a narrow beam of light will cause the plant to turn white and die back. An inch from that beam and the plants will thrive. Easy fix is to hang the light up higher for better coverage and reduce the intensity.

Do fish prefer white or blue light? ›

Like guppies and rotan, some types of fish develop better from fry to adult under blue light. Other species of fish prefer green light, and most don't grow as well under red light.

What color light is best for freshwater aquarium? ›

FULL RGB SPECTRUM

This is our go-to spectrum and we HIGHLY recommend this spectrum for most freshwater aquariums. Nothing brings out the vivid colors and enhances your tank like a full, rich RGB (Red,Green,Blue) spectrum of light. It not only makes your fish pop in color, it also won't promote algae growth.

What is the best lighting for freshwater aquariums? ›

Your best lighting options for freshwater aquariums are standard fluorescent bulbs, compact fluorescent bulbs, metal halide lights, and LED lights. You want to avoid incandescent bulbs as they are suitable only for small aquariums and can give off too much heat.

What is a full spectrum aquarium light? ›

Full Spectrum/Daylight Bulbs - Emit all the wavelengths of visible light and closely approximates the visual effects of natural sunlight. Contains a blend of all the colors of the color spectrum. These general-purpose bulbs are ideal for all types of fresh and saltwater aquariums.

Are aquarium lights the same as grow lights? ›

As we know, grow light is designed to provide a light spectrum similar to that of the sun. And additionally, you can create a spectrum that is more tailored to the needs of the plant being grown. On the other hand, regular aquarium lights are less focused on emitting the right spectrum and more on illumination.

Should I turn off my aquarium light at night? ›

Aquarium fish do not need light and it is best that you turn it off during the night. Leaving the light on can cause stress to fish as they need a period of darkness to sleep. Too much light will cause algae to rapidly grow and make your tank look dirty. So the short answer is no, do not leave your lights on.

Is moonlight good for aquarium? ›

Another important benefit of Lunar LED light applies specifically to saltwater and reef aquariums. Moonlight triggers natural biological activities, both internal and external, for a variety of reef-dwelling creatures and it plays a very important role in the growth and spawning of corals, specifically.

Is moonlight good for fish? ›

Benefits of Moonlight for Reef Tanks

In the case of aquarium moonlights, the benefits are many: They offer nocturnal creatures precious illumination to aid in nighttime foraging activities. They provide comfort to diurnal species that might become scared in total darkness.

What fish will glow under blue light? ›

Bringing Color to Life!

GloFish® fluorescent fish come in a variety of species and colors of tropical fish. From bettas and danios to tetras, barbs and even sharks - all are brilliant under white LEDs and their color dazzles under blue LEDs!

How many lumens do I need for planted aquarium? ›

That all depends upon which plants you have chosen for your aquarium. If you have chosen nothing but "Easy" plants, 10-20 lumen (0.25 to 0.5 watts) per litre is adequate. For "Medium" plants, we recommend 20-40 lumen (0.5 to 1 watts) per litre, while "Advanced" plants require more than 40 lumens (1 watt) per litre.

Do fish like blue light? ›

Blue is associated with calmness and serenity. It's also known to have an astringent effect. So, yes, blue light definitely helps calm the fish and encourages their bodies to slow down and rest. Also, the blue light in the tank helps to mimic the natural moonlight that fish are exposed to in the wild.

How long can aquarium plants go without light? ›

Aquarium plants can live up to 3 days without light, but for more fragile plants I would definitely recommend keeping it under 2 days. Leaves will turn pale quickly, and can in turn weaken the plan.

How many lumens do I need for aquarium plants? ›

Lighting information for Planted Tanks

Here I have tried to create a basic guideline about how much and how often you should give lights to your aquarium plants for better growth. Lumen: Plants that require low light do fine on just 15 to 25 lumen.

Are LED lights good for planted aquariums? ›

Will aquarium plants grow under LED light? Yes, aquarium plants will definitely grow under LED as long as the light emits in the right spectrum. Regular white LEDs are great and will allow your plants to thrive. Just make sure you know what brightness your plants desire.

What type of light is best for freshwater aquarium? ›

Your best lighting options for freshwater aquariums are standard fluorescent bulbs, compact fluorescent bulbs, metal halide lights, and LED lights. You want to avoid incandescent bulbs as they are suitable only for small aquariums and can give off too much heat.

Are LED aquarium lights good for plants? ›

LED lighting is an excellent choice as aquarium light for plants.

Can you have too much light in a planted tank? ›

Most people turn on their aquarium lights between 8 to 10 hours per day. The duration can vary depending on the brightness of your light, the needs of the specific plant and the ambient light in the room. Too much light can cause excessive algae growth.

Can aquarium lights be too bright? ›

But in general, the lighting shouldn't be too bright for a regular tank since it could stress the fish. Too-bright lighting can also lead to algae growth.

How many LED watts per gallon planted tank? ›

How much watt LED is needed for the planted tank? In general, you need about 1-5 watts per gallon to light a planted tank.

Will algae grow under LED lights? ›

Contrary to what you may have been told, LED lights do not cause algae growth any more than other aquarium lighting options.

What does a blue light do in an aquarium? ›

Blue LED lighting creates a calming ambiance in your aquarium. Many fish enthusiasts say the blue light serves best as a transition light between light and darkness. So, you can use the light in the evenings to help your less curious fish to come out of the hiding spots as blue light mimics the moonlight.

Does Bluelight stress fish? ›

It's also known to have an astringent effect. So, yes, blue light definitely helps calm the fish and encourages their bodies to slow down and rest. Also, the blue light in the tank helps to mimic the natural moonlight that fish are exposed to in the wild.

What color LED light is best for fish? ›

FULL RGB SPECTRUM

This is our go-to spectrum and we HIGHLY recommend this spectrum for most freshwater aquariums. Nothing brings out the vivid colors and enhances your tank like a full, rich RGB (Red,Green,Blue) spectrum of light. It not only makes your fish pop in color, it also won't promote algae growth.

Should I turn fish light off at night? ›

Aquarium fish do not need light and it is best that you turn it off during the night. Leaving the light on can cause stress to fish as they need a period of darkness to sleep. Too much light will cause algae to rapidly grow and make your tank look dirty. So the short answer is no, do not leave your lights on.

What is the best background color for fish tank? ›

Light blue is a safe choice. Fishes can easily be seen against a light blue background as the background provides a good contrast to the fish. Even blue colored fishes, of which there are really very few species, can be seen.

Why do my aquarium plants keep floating? ›

Aquarium plants are lighter than water. That is why they start floating on the surface instead of going deep down. You have to anchor the plants properly so that their roots can grow deeper and they can get stable.

Is purple light good for aquarium plants? ›

Plants use very little yellow, orange, violet, and almost no green light. These colors are present in bulbs so that you can see them reflected off your plants, animals, and décor. They are important for creating a vibrant, beautiful aquarium, but not for actual plant growth.

Videos

1. Planted Aquarium Lighting Guide - Introduction - Part 1
(The Water Box)
2. Aquascape Guide - Selecting a Light For a Planted Aquarium / EP 2 - Lighting
(Aquascape Guide)
3. Aquascaping 101 Tutorial: Planted Tank Lighting
(Aquascape Supply)
4. Advanced guide to lighting a planted tank - Choosing light fixtures
(Dennis Wong)
5. Planted Tank Lighting Conclusions - Planted Aquarium Lighting Guide – Part 8
(The Water Box)
6. Advanced guide to lighting a planted tank - Basics first
(Dennis Wong)
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