Your Cart is Empty
Understanding planted aquarium LED lighting
Introduction
Aquarium lights are the power house of any planted aquarium. They power plant photosynthesis, but also play an equally important role in rendering attractive visual color tones of both fish and plants. There have been tremendous improvements in LED technology in the past 10 years for aquarium plant lights. Modern LED lights are more energy efficient, more powerful than older light systems such as T5 fluorescent tubes, and many light systems can also enhance the visual color tones of plants and fish.
Many modern light systems give a wide range of features, from spectrum tuning and in-build timers. Some lights even have fancy programming such as simulating lightning or a disco show, but such features are gimmicks and offer little real value in the long run. The choices can be bewildering for new aquarists and in this article we will focus on the few key aspects of choosing a light for your planted aquarium.
Cardinal tetras under Week aqua M600
Hyphessobrycon wadai under Week aqua a430
Tank top vs hung lights
Lights can be hung from the ceiling for a cleaner presentation for rimless tanks or they can be mounted on the edges of aquariums. Raising the lights a far distance from the tank significantly lower light levels within the tank. However, pendant lights designed to be hung a distance away from the tank takes this into account and are usually quite high powered to compensate. While it takes quite a bit of effort to hang lights, having clearance on the top of the tank gives great views and easy access for tank maintenance.
Light above: Twinstar S series sitting on rimless tank's edge.
Pendant lights attached to ceiling: Week aqua a430.
Pendant light offers easy access to tank and great top views: LEDSTAR AQ-X
So what really matters? 3 important factors to evaluate a light fixture
Power |
Spectrum |
Coverage |
Factor 1: Power - measured in umols of PAR
PAR (Photosynthetically Active Radiation) is the most accurate measure of the 'strength' of light relevant to plant growth, as it directly measures the amount of light available for plant photosynthesis. It counts all photons between 400-700 nanometer range, which is what plants use for photosynthesis.
Click here for information on which part of the light spectrum powers photosynthesis.
PAR figures are provided by most reputable luminaire manufacturers in the form of PAR charts. One can also refer to PAR data taken by hobbyists who own PAR meters. What if no PAR tables or hobbyist data are available? The other way to judge whether a light will grow the plants you want is to see tanks with that particular light. If other hobbyists using the same lamp can grow the same plants you want to grow, chances are it will work. Many more powerful LED units produced today allow one to tune up or down the amount of light produced.
Click here for information on how to read manufacturers' PAR charts.
Moving a PAR meter around the tank shows that PAR levels at the top of the tank near the light fixture can have many times the light levels hitting the substrate level. The rate at which PAR drops off with aquarium depth depends on a few factors and is often not completely linear. This is because the glass walls internally reflect light and different light units may produce more focused or diffused lighting which affects how effectively light penetrates water.
How much PAR should a tank have?
When folks say that they are using 100 umols of PAR in their aquarium, this is usually the average measurement taken at the substrate level of the aquarium. The broad guidelines as commonly used by the aquatic plant community are as follows:
| PAR Values | Suitable for |
| 20 to 40 umols |
Low light levels - suitable for shade aquarium plants such as Anubias, Java fern, Cryptocoryne and mosses. Light levels are so low, algae is easily dealt with. |
| 40 to 90 umols |
Medium light levels - With good CO2 levels, you can grow most common aquarium plants, and can good colours for red plants at the higher end of the range. Good for Iwagumi and nature-style aquascapes. Carpeting plants grow at good speed at this level of light. |
| 90 to 150 umols |
High light levels - Great for bringing out colouration for red/non-green aquarium plants and cultivating demanding species. High light levels give greater density and speed to plant growth. However, this level of lighting requires good control of aquarium cleanliness and plant health to avoid algae problems.
|
| 150 umols + |
Very high light levels - Sun tanning effect on red/non green plants to produce the most intense color tones. Allows even greater plant density and tightly stacked bushes. Requires expert maintenance for a tank to be algae free.
|
Contrary to popular belief, carpeting plants such as Dwarf hair grass do not need a ton of light to grow well. Iwagumi aquascapes are better off using the lower end of Medium light levels - this minimizes algae.
Tank with coloured stem plants grown with 150 umols of PAR on the substrate level. This means that at mid and higher levels of the tank, the plants are receiving 200-300umols of PAR. This PAR level gives good coloration and density to stem plant bushes.
Higher light levels give an edge in propagating difficult species and give great coloration and density to colored plants. Rotala florida, and Eriocaulon quinguangulare are two picky, light demanding species. Grown here under 250 umols of PAR at substrate from a Week aqua a430 fixture. About 300+ umols of PAR is hitting the purple Rotala florida bush.
What are Lumens ?
Lumens are quoted by some outdated websites, but Lumens is a poor unit of measurement because it measures the brightness of light with respect to the sensitivity of the human eye. This means that lights that are high in green wavelengths have a higher lumen rating because the human eye is more sensitive to green than red or blue. However, plants 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.
Trend of over-powered lights
Do you need 167 umols of PAR to grow Anubias and Java fern in a low tech tank? Probably not, and running excessively high light exacerbates algae issues.
Due to industry competition, aquarium light units have become more and more powerful over time. Higher end units of popular brands such as Week aqua, Netlea, Chihiros, produce a tremendous amount of light for their given size. Using much more light than what is necessary to achieve their tank goals is the downfall of many inexperience aquarists.
Most carpets and common plants can grow even as low as 40 umols of PAR as long as CO2 levels are sufficient. Most powerful LED units have controls that allow one to tune down the power level - folks should start their planted aquariums with lower light levels and adjust upwards as their tanks grow in.
Factor 2: Colour spectrum
Any light that produces enough PAR can grow plants. The main reason aquarium fixtures cost more than industrial floodlights is that they render plant and fish colours better. Below is a comparison of cheap household lights vs higher end aquarium specific light units on the same tank.
Another comparison pic taken from the internet:
It is the same tank in both pictures above. The Fluval 3.0 produces terrible color rendition compared to the Netlea AT5.
The chief role of colour spectrum in LED lighting is to light up the tank in a visually attractive manner. Colour spectrum has some impact on plant growth form and colouration, but these concerns are dwarfed by the visual aspect that aquarium lights play.
The way best to choose a colour spectrum profile that works for you is by seeing an aquarium lit by the light unit you are interested in. The visual colour hues in real life can be quite different to what one sees in photographs, especially for folks with sensitive eyes. Modern LED units can oversaturate certain colours (or under saturate them depending on what look you prefer). The alternative is by judging aquariums based on well taken photographs.
Lights with tunable spectrum can present quite a range of colour tones depending on the exact ratios used for the Red/Green/Blue diodes. Aquarists are spoilt for choice with the spectrum tuning capabilities of most modern LEDs.
To read more on how to read light spectrum charts and read in-depth about what makes a great LED spectrum go to here.
R=Red, G=Green, B=Blue, diode settings for the pictures. Aquarium on the right has the most neutral colour tone, with increasing blue spectrum towards the left.
Top left has the most neutral colour spectrum programming, shifting to increased red and blue at top right, and even more increased in red and blue spectrum in the bottom row.
If you like lights that give strong colour saturation to red and other coloured plants, and have spectrum tuning to give shifts in colour tone, the following brands offers great value for their pricing: Week aqua, Netlea, Chihiros, Twinstar (S Series), LEDstar (AQ-X), ADA solar RGB. Their light units are powerful, and higher end units all come with spectrum control and in-build timers.
Week aqua and Netlea LEDs offer a tad more colour saturation in real life than the Twinstar III S series, however they can look very similar in photographs. All 3 offer attractive colour rendition. If you want to spot small differences in spectrum for LED fixtures, you must do a real life comparison.
If I get an LED light with spectrum tuning, does it mean that I can get any color tone?
The short answer is no. LED lights with spectrum tuning make use of Red/Green/Blue diodes which produce white light when used in combination. You can shift the light's colour tone towards Red/Green/Blue by changing the ratio of power to each coloured diode. However, each coloured diode is of a fixed colour denoted by its nanometer designation. Some brands use brighter red diodes (shorter wavelengths in the red spectrum) while some brands uses deeper red diodes (longer wavelengths in the red spectrum). The brands that make use of deeper red diodes will always render red plants a shade of red darker compared to say brands that use brighter red diodes.
For example, ADA solar RGB (below), uses deeper green diodes compared to say Week aqua LEDs. So the ADA solar RGB will always render green tones a shade of darker green compared to a Week aqua LED which render greens in brighter green tones. No amount of adjusting of RGB values on either set can make them render a tank the same way.
Photo from Viktor Lantos, Green aqua, showing ADA solar RGB.
Does CRI (Color Rendering Index) rating matter?
Does a higher CRI rating on the luminaire make a difference? In short, it does not. For most aquarists, colour accuracy is not as important as colour saturation. The CRI measures the colour accuracy of lighting units, whereas hobbyists overwhelmingly prefer lighting that has high colour saturation and contrast. The tank below is lit by a custom LED unit with a CRI score of just 78.
This article explains how the CRI is actually calculated, and why it does not really matter.
Is K rating important?
No other subject is as full of misinformation and marketing gimmicks as aquarium lighting, for example the idea that 6500K is an "ideal" spectrum because it matches the colour hue of the sun. The K rating is not a good indicator of whether or not a light is suitable for growing plants. It simply measures the visual hue of the light (as perceived by human color vision). Visual color hues can hint at the underlying spectrum profile of a light, but it does not fully describe the underlying spectrum profile.
We have demonstrated growing a wide range of tanks successfully across a large range of K rating values.
A mix of tanks grown under different K-rating lights.
Click here to read more in-depth what the K rating actually measures.
Does a light need to be "Full spectrum" to work well?
"Full spectrum" is also a marketing term that has nothing to do with how well a light grows plants. Any white light can be described as full spectrum as all white lights contain the key red, green, blue wavelengths of light by default. Furthermore, you can grow plants just as well without full spectrum light. For example, the International Space Station uses only red and blue LED diodes to grow plants.
Many biology textbooks have yet to be updated to reflect new data in this area, such as the fact that plants use a significant amount of green light for photosynthesis.
Factor 3: Coverage
It is important that the coverage of the fixture matches the dimensions of the tank. We have found that dual LED fixtures works better than a single light bar for complex hardscapes with shaded areas, as having two or more light sources tends to reach most areas of the planted tank. A low spread fixture (e.g. single point) will have very high PAR in certain areas (often the centre of the fixture) while the edges will be shaded.
Point source lights have circular areas of coverage and are best suited to square planted aquariums or tanks that can be divided into squares with minimal overlap. Rocks and other tall hardscape can easily block point source light from reaching the plants. Using 2 fixtures, front/back, or going for lighting kits that come in an array may work better.
A single wide-angle LED lightbar has a dispersion pattern where higher parts of the hardscape can block light from reaching plants behind the hardscape. Object simulated by the blue block in the diagram.
A more distributed light source (above), such as a wider LED array will not have a similar problem.
Raising pendant lights higher gives better spread but a lot of light will be cast outside of the tank. However, most modern pendant lights are quite powerful to compensate for such usage. Aquarium lit by Chihiros vivid 2.
Using a pendant light system that is shorter than the length of the tank in this example leads to deeply shadowed areas to both the left and right sides of the tank where light is partially blocked by the wood hardscape, leading to poor plant growth in those areas. This can be corrected by using hardscape decorations or shade plants in the shaded areas instead.
Here are links to further reading:
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
unlock your true potential
Grow anything, defeat algae, create amazing aquascapes
