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PUR, PAS, PAR in Aquarium Reef/Planted Lighting; LED Wavelengths
By Carl Strohmeyer-PAMR 35+ years experience
- Lighting Overview
- Water Depths & PUR Plant & Corals; Including Acropora Reefs:
- RQE, PAR Meter Use
- Real World Application of RQE, PAR. PUR, PAS, & Photons
- Further Depth Penetration Information
Lighting Overview (Planted & Reef Aquarium):
This article is to understand how we can achieve optimum lighting for growth of a photosynthetic organism in our planted freshwater & reef aquariums, while considering having a limited artificial energy source, like a aquarium light fixture. We know we cannot create the amount of useable light the Sun gives, so we try to optimize the light we are able to make for a given about of watts (input energy).
I should note that a lot of aquarium lighting use history has gone into this subject, as we already know based on use of "warm white" fluorescent shop lights in the 1970s that we can grow plants, just not as efficiently as the lights we have now (Advanced reef keeping was not even possible with the available lights then).
So for some aquarium lighting experts to dismiss subjects such as the concept PUR as "theory" I have to respectfully disagree and I would state that this is showing a lack of knowledge or experience of the history of aquarium lighting.
We know that many man made white sources will grow plants, how well depending upon the PAR at the level where the plants are located (PPFD) and the efficiency of the often limited light energy we can provide (PUR).
However, we also know based on aquarium lighting history that when tri-chromatic, actinic and other "tuned" spectrum light sources were employed, in other words PUR, we did a better job growing these plants and eventually photosynthetic corals, etc. with the same exact input wattages.
Example: 40 watt warm white versus a 40 watt Trichromatic or a 40 watt cool white versus a 20 watt trichromatic plus a 20 watt actinic for anemone aquariums.
In the end, we know that long before the advent of LED lighting, improved PUR would provide more light energy for the same given input energy, which is why along with other efficiencies (including drivers, etc.) the many economy LED lights such as the Finnex require as much as 4-5 times the input wattage as a better higher efficiency LED, often making any savings go out the window.
Related as per the importance of knowing aquarium keeping history: Bioavailable Carbon - CO2 and a Proper Gas Exchange---
PUR stands for Photosynthetically Useable Radiation. It is also sometimes simply known as "useful light energy".
Another description could be: "Quality of light per application" compared to PAR (Photosynthetically Active Radiation) being the "quantity of light energy" used by photosynthetic life.
I think many in the hobby get "hung up" on this term, as it is a "fuzzy term (which I would partly agree since each plant, coral, etc, can be unique), but there are many aspects of science such as we have moved through the discovery of subatomic particles that are based on subatomic behavior, but not as easily measurable such as PAR is.
As well, we also know based on aquarium lighting history that we simply cannot dismiss the evidence supporting PUR as a fact either. It is unfortunate that many in this hobby will dismiss this term which has been around long before many even were born. The FACTS are, it was and is a useful term in that we knew decades ago that there was a pronounced difference in many fluorescent lights when everything else was equal; from input watts, lumens, length, type, etc and the only difference was the spectral output (PUR).---
In the application of considering most the "useful" energy for plant or zooxanthellae mass growth, we need to consider the measurements of light, which triggers the main fuels for photosynthesis.
PPFD stands for photosynthetic photon flux density.
PPFD is a measure of the number of photons in the 400-700nm PAR range (photosynthetic active radiation) that fall on a square meter of target area per second. This is noteworthy since many light manufacturers might state high PAR numbers directly under the light source, but not at say 400mm (which is a more scientific measuring point employed by more reputable manufacturers). If that light energy isn’t getting to the target, along with less optimal PUR, you are not going to have as effective a light source for the input energy used. (Reference #20)
Another way to phrase PPFD is this is PAR at a distance, which in water can mean more energetic spectrums that penetrate deeper such as blues/violets, but may not necessarily be the optimal light energy for a given photosynthetic organism at a certain point in their growth cycle.
Photosynthetic Action Spectrum (PAS) describes the "rate of a physiological activity plotted against wavelength of light" for a given biological component of an organism. In this case, it would be chlorophyll A&B (main growth of a plant or coral zooxanthellae. (Reference #11).
PUR is a more broad and generic term here, since it can be used in other applications, like the overall useful radiation (PAR) for best plant health, not just growth.
PAS more addresses the specifics, since this is where the light energy (photons) activate photosynthesis. Another way to look at this (an analogy using biology), is that proteins are made up of amino acids, of which we know the specific amino acids we need for our physiological processes. Ditto PAS, which describes the specific action spectrums where photons begin photosynthesis.
PUR and more specifically PAS differs from PAR, because the basic definition of PAR is ANY light in the spectral range (wave band) of solar radiation from 400 to 700 nanometers, which photosynthetic organisms are able to use in the process of photosynthesis (Reference #12).
PUR is the usable portion of PAR or better is defined as the photosynthetically available radiant energy of such wavelengths, which can be absorbed by the algal and plant pigments more efficiently. Or stated another way, the photons of light at frequencies most readily usable for photosynthetic life, keeping mind that a photon is a photon, and they differ based frequency (more or less energized/energetic)
PAS is where an "action" begins of utilization of light energy by the photosynthetic life.
Of this "action spectrum" (as shown in the graph to the above left), we know the general range of photosynthetic response for most photosynthetic life forms. However, there are slight variations among different photosynthetic species, which will have a different PUR range to which they respond optimally.
Even within these variations, we do know certain wave lengths, such as green/yellow are generally less efficient for growth (mass) when considering trying to get the best growth with the limited input energy. OR in other words, getting the more useful output energy for the given input energy.
As noted in PUR (reaction) and PAS (action), there are variations in plants, aquatic plants, and zooxanthellae, in what these optimum exacting spectrums may be.
In nature, often these are influenced environmental differences, such as water depths, which will filter out red light spectrums more than blue, since blue is of a higher frequency, which can pass deeper into water (or even plant tissue). This is why zooxanthellae will generally require higher "spikes" in the blue spectrums.
However what we do know are the generalizations of what these photosynthetic action spectrums are.
As a simplified example; if one were to use a scale of 1 to 100 to represent PAR, and say one species might need more at 15 while another need more light energy at 20, these still fall within what we know as PUR. What we also know is that any light, which has its primary energy at 50 on our simplified scale, this middle energy is at least as 30% less efficient by itself for the vast majority of photosynthetic life intentionally kept in aquariums or grown in vertical farms. Yet, we also know based on studies, there appears to be a certain synergy from all wavelengths, which can aid in growth.
Further References (there are many more reference throughout and at the end of this article):
*Aquarium Lighting; PUR
*St. Mary's College LED Experiments
In the St. Mary's reference we see evidence of what LEDs using more precise PUR/PAS emitter/LED technology can do for coral growth.
Here is a more recent update from St. Mary's utilizing high efficiency LED lighting:
Sustainable Science Thesis & Abstract Update
In a recent CBS news story, a large "Vertical Farm" in Portage, Indiana is using LED lights, which are specific to the light energy used most efficiently by plants, NOT PAR (combined usefulness from all light), which so many aquarium keepers seem greatly confused by.
This farm uses just the red and blue spectrum emitters, NOT additional green emitters or other emitters such as cool or warm white, which are used by some of the most popular LED fixtures. These emitters might be pleasing to us and certainly have useful light energy too, but it's demonstrative that these are simply less efficient. Better for our aquatic use might be more efficient emitters using high amounts of energy in useful blue and a overall spectrum including all colors (including. green and yellow) (such as the Cree XB-D 6500K). This gives us the "useful" PAS, with the "useful" PAR.
This is a real world application, which shows where NOT JUST using lighting, which are high in CRI (Green-Yellow) (pleasing to us), rather lights specifically using applicable PAS.
Just using PAS would use the least amount of input energy for output of useful light energy.
The billion dollar question as of 2016 is how to create the most effective white light (all color light mixed), considering how effective all the colors in the white light produce photosynthesis.
This question can be asked of PUR/PAS naysayers:
Why would a business use lighting, which might look better by containing all PAR light spectrums, including more yellow and green (common with most aquarium LED lights in varying amounts, including the AquaRay, EcoTech, BML, and more, many of whom do not even publish their emitter spectrograms), but then would use more electricity, when using ONLY optimum wavelength/frequency lighting would produce the same or better results for much less electricity costs?
To be blunt, part of the problem is the aquarium hobby being a "non essential business", often thrives on hype and marketing. But when it comes to well funded research in horticultural businesses, they can care less about this hype and go with what works best of the lowest input energy for the most output energy.
Reference: Vertical farms: "Making nature better"
This targeting of optimum wavelength lighting is becoming more and more widespread in industry, it's only a few in the aquarium hobby that are behind the curve.
Why this becomes important is understanding the differences in growth when not considering PUR/PAS, when we have a limited energy source, such as as light fixture.
Fixtures focused on PUR/PAS produce far more growth than fixtures not using high PUR fixtures. Growth is night and day, with less than optimum PUR/PAS fixtures taking far more energy to produce typical growth. They might even produce less than typical growth. Certainly not optimum growth.
I'm NOT saying LED lights (or other lights) with high percentages of green, yellow or use of cool/warm white emitters cannot keep photosynthetic life, only that this is just one reason why a light of lower PAR and input wattage, can actually produce more optimum wavelength or output energy.
As an aquarium keeper, we certainly want our corals and plants to look pleasing, but often this comes at the expense of more wasted light energy then needed. This is also not a new question/problem, as this goes back to the use of T12 fluorescent lights too where we later moved on to more efficient T6 & T5 lights.
For clarity, let me emphasize that I am NOT stating PAR is not an important measurement, just that this "light measurement" should never be the only consideration in determining the best light for your reef, planted or even just mixed aquarium. Understanding how much of the PAR is focused the important PAS, which becomes critical in aquarium lighting.
With LEDs, we are able to select nanometers of lighting, we wish to focus our energy.
Just using one brand so as to be comparing "apples to apples", the AquaRay Fiji Blue (about 450nm) and Marine White (10,000k) #600 LED strips both have the same input energy (12 watts), the same drivers, the only difference being the emitter spectrums. Yet the PAR at 400mm (output energy) from the Marine White is considerable higher than the Fiji Blue.
Does this make the Marine White superior to the Fiji Blue? The answer is not necessarily as it depends upon the application. In this same line of fixtures the Reef White #600 also has a lower PAR than the Marine White #600, yet in most reef applications deeper than 12" of water, the Reef White would be the better choice!!
The aquarium above is a planted 75 gallon aquarium utilizing two GroBeam LED lights. It's kept "low tech" with no added CO2 other than Flourish Excel and minimal other supplements. The only high tech aspect of this aquarium is the LED lighting, which uses high PUR/PAR, licensed emitters, and PWM technology.
The aquarium to the right is a planted tank utilizing (4) TMC Aquaray Growbeam Ultima 600's before and after pruning.
This growth happens in about 2 weeks.
Also used in the 2nd tank: 1500 TMC FSB Filter, AAP Sunsun canister, NilocG EI Ferts, AAP Wonder Shells (Courtesy Chris O'Hara)
Besides of course the measurement of output energy (PAR, also called Photosynthetic Photon Flux Density, which is a measure of the number of photons), Useful Light Energy/PUR/Optimum Wavelength has become one of the more important aspects of choosing an aquarium light since the advent of high end Aquarium LED Light Fixtures.
By high end I mean better and targeted emitter bins, advanced drivers/circuitry versus the many low end LED fixtures available (generally out of China), which essentially are not much better that household LED emitters (Christmas lights) daisy chained together with even much of the input energy wasted as heat energy before it even becomes PAR photons of energy.
Since even the best of fluorescent lights such as T5, T2, and SHOs still emit a considerable amount of light energy in light spectrums not targeted for photosynthetic life, acquainting oneself with this aspect of light energy is very important if you are considering a new light fixture, especially a high end LED (such as the TMC AquaRay).
Water Depths & PUR Plant & Corals; Including Acropora Reefs:
Environmental factors for natural light and water penetration.
PUR & PAS are also affected by water depths, with blue light around 420-480nm (within the PAR range) having the best useful depth penetration (including for our aquariums).
This is an important note for many zooanthellic algae symbiotic dependent corals, clams, etc. in choosing the correct light as well as per specimen placement to achieve the best PAS/PUR light energy.
The picture to the above left shows Spectral Light Absorption in certain water depths.
What is noteworthy is that essential near red light energy becomes less viable not much under water surface, as per PAR requirements of Photosynthetic response and Chlorophyll synthesis of plants and green algae.
Further Reference: Aquarium Lighting, PAR, Photosynthetic Response
Plants and zooanthellic algae have adapted to certain depths and is why a 6500K (white light focused in the middle of the visual spectrum) light generally works well (or best) for planted freshwater or refugium aquariums under 20-24 inches of water. While zooanthellic algae dependent corals require more blue and higher kelvin daylight energy such as 9000K, 10,000K, 14,000K, & 20,000K lights (more intense energy), because of the more energy corals need and the depth as aquarium depths increase (such as 24+ inches of water depth).
Even in a planted tank over say over 24" in depth a higher Kelvin temperature light such as 8500K might be better, when more energy is needed for higher demanding plants.
With this information about actual sunlight penetration, we can safely make some accurate assumptions, even if relatively general.
As you can see, the Photosynthetic response and Chlorophyll synthesis do NOT penetrate much past 25 and 50 meters of water respectively.
So using Acropora Coral as an example, these have been found at varying depths mostly less than 25 meters, but generally thrive at 6 meters, producing an environment, which is deficient in these photosynthetic response and Chlorophyll synthesis light PAR spikes would result in less than optimal results.
What the above means to the aquarium keeper is no artificial light; not LED or Metal Halide or any other is going to be equivalent to the energy of the Sun (tropics at noon is closer to 6500K at the surface of water).
So using a 20,000K fluorescent, Metal Halide 20,000K, or LED setup that is 2/3 blue is likely NOT going to produce optimum results in a tank of approximately 20 inches or less of depth.
With this lighting in a shallow tank you're more than likely producing environment, which simulates many meters deeper than optimum. This still might be fine if this is the depth the specimens being kept are naturally adapted to as per specific wavelengths of light (nanometers).
Of course this begs the question of what the comparison would be and at this point I don't have a scientific equivalent (maybe there's one, but this would be difficult with the plethora of lighting choices and their subtle differences).
The picture to the left clears up the confusion in my opinion (& experience too), since this displays an aquarium lit with 20,000K lighting and a natural Acropora reef.
It's obvious the aquarium is much more blue than the natural reef.
However, since NO artificial light, the best LEDs or even Metal Halide (such as the top notch "Radion" 20K MH) can approach the Sun's energy even in the color temperatures, which make up CRI (what looks best to us). The result is it often takes more "blue" appearing man made light energy to achieve the best possible PUR/PAR for your aquarium 'reef'. Often man-made lights, in particular many of the Johnny-come-lately LEDs will utilize lower kelvin white emitters and red emitters in an attempt to make a more human pleasing light, but as a result often waste more energy outside the essential PUR spikes needed by photosynthetic reef life.
Further Information: Aquarium Lighting; CRI
To the left is a picture of a 150 gallon reef aquarium that also has Acropora corals (for 6 months at the time of the picture).
PLEASE NOTE; this picture is much closer in color to the natural Acropora reef than the 20,000K light aquarium to the left in the picture above that is unfortunately more common with how many light their aquariums with Metal Halide or LED lights.
The picture to the left is courtesy of "Aquarium Lighting, Facts & Information"
This Reef tank is running AquaRay/AquaBeam NP 1500 & 2000 tiles which employ the more natural patented Osram Olson NP Blue emitters.
What is also noteworthy is that PAR readings taken in 2011 on Bali Island at a coral farm, is that they kept corals for best growth about 1.5-2 meters under water surface. For best pigment intensification, even deeper; 3.5-4 meters.
Here is the point, the average PAR reading was 160 and never exceeded 200, not the higher reading often cited by many for their high intensity lights, especially Metal Halide.
WHY, quite obviously they is much more at play than just PAR and many of the best lights, including Metal Halides simply make up for lack of optimum PUR with higher PAR numbers than needed, in other words while quantity of light is most important, there is still a quality of light too!!!
The previously noted comparison picture also makes the point that while at 6 meters, an Acropora Coral colony is not all that deep by ocean standards, but try getting your Metal Halide, T5, or LED light to penetrate 6 meters (over 18 feet)!!
This then can be applied to lighting our standard high (24" inch aquarium), for whatever we are trying to growth (plants, harder plants, soft coral, hard coral).
This is why we MUST pick a light, which will closest meet these key photosynthetic response 'spikes' (PAS), while still considering more intense energy is needed (from more blue light), more depth is involved, and the all the other light needed for photosynthesis (PAS), as well as consideration of RQE (discussed more in the next section). Rather than pick a light, which most looks like the sunlight underwater at a certain depth to our eyes.
This said, one LED emitter SPECIFICALLY designed for reef life, the Osram Olson NP Blue emitter is probably the closest to this same softer white/blue found naturally in reef containing Acropora coral, while producing more intense energy found in higher kelivn ratings of lights (Such as 20K-50K).
What is also noteworthy and a popular trend is the use of "Near Ultraviolet" emitters (basically roughly between 300-400nm UVB- mostly UVA). This is intended to give a cool "pop" to many LPS and SPS corals, but what readers should note is that EVERY watt of energy used for these emitters is mostly useless for your photosynthetic corals as it is outside the known PAR/PUR spectrums.
This simply is a fad, which many LED manufacturers are following, including EcoTech and TMC AquaRay. At least with AquaRay they came out with this NUV emitter in a 600 Ultima fixture, which is a separate supplemental light, NOT as part of a premier self contained reef light fixture as EcoTech has done.
Quantum PAR Meters & Relative Quantum Efficiency (RQE):
These are a useful tool, in fact often the starting point for measure light "usefulness" in measuring light photon quantity. But it is sometimes over used for determining how effective a light is if other aspects are ignored. I will give a brief explanation along with resources about their use.
Here is an excellent description of what a PAR meter measures:
"When measured in photon terms, PAR is also called Photosynthetic Photon Flux Density (PPFD), which is a measure of the number of photons in the 400 nm to 700 nm waveband that are incident per unit time on a unit surface. When expressed in photon terms, all the photons are considered equal (Red Line), independent of their energy. The quantity of photons is measured in moles of photons (1 mole of photons = 6.022 x 1023 photons = 1 Einstein). In practice, PPFD is measured in microEinstein/m2/second, or µE/s*m2"."
Referenced from: http://www.personal.psu.edu/sbj4/aquarium/articles/MetalHalideLamps1.htm
It is noteworthy that a PAR Meter is not 100% accurate in important light energy spikes WITHIN the 400 to 700 nanometer range, so while one light might measure a higher PAR mmol reading, another light might be still superior due to the more wavelength output one is trying to achieve.
An example could be the 6500K Daylight XB-D emitters with 12 watts of input energy, and the same drivers with a PAR of 61 µMolm versus the same exact fixture with XT-E blue emitters with a PAR of 38 µMolm. Does this mean the Daylight fixture is superior or higher "quality" of light output? NO, as it depends upon the application where the daylight fixture might be better for a planted aquarium application, while the 450 nm XT-E blue might be a better choice as part of a reef lighting application.
We now also have some very pricey PAR meters (Li-Cor PAR Meter) (Measure Yeild Photon Flux (YPF) Mcree Weighted PAR) that can measure approximately 390nm to 720nm, and much more accurately within these parameters. This might be the better choice for those looking to get more scientific about their lighting, especially with new research showing use of light outside the accepted PAR being utilized. Li-Cor meters do not consider photons equal (Green Line).
"Quantum efficiency"; this term generally refers to the efficiency to incident photon to converted electron (IPCE) ratio of a photosynthesis.
This does not mean that this is the PUR/wavelength (or photosynthetic action spectrum-PAS) of a Zooxanthellae or plant, but does give an idea of overall PUR (PAR/YPF/RQE) of all light working together for photosynthesis.
To the left is a graph showing the Relative quantum efficiency curve (aka the McCree Curve of 1972). This is related to the photosynthetic action spectrum of photosynthetic plants, algae, and Zooxanthellae
According to the quantum theory, radiant energy is transmitted and absorbed in discrete particles called quanta or photons which this curve "predicts" the efficiency and CO2 assimilation rates.
Along with the quantum theory, we have the electromagnetic theory that together in my understanding provide the most relevant explanation of those characteristics of radiant energy that are useful for understanding photosynthetic requirements and illumination. Besides the quantum theory, the electromagnetic theory states that the radiant energy is propagated in the form of an electromagnetic wave. As with any wave, radiant energy has a wavelength and a frequency associated with it. The wavelengths of light are usually expressed in nanometers, where 1 nm = 1 billionth of a meter.
Plants usually convert light into chemical energy with a photosynthetic efficiency of 3–6%. Any absorbed light that is unconverted is dissipated primarily as heat, with a small fraction (1-2%) re-emitted as chlorophyll fluorescence at longer wavelengths.
Actual plants' photosynthetic efficiency varies with the frequency of the light being converted, light intensity, temperature and proportion of carbon dioxide in the atmosphere, and can vary from 0.1% to 8%.
This curve/graph has been used a lot of late, and it certainly holds a lot of merit, showing that green light is indeed used in photosynthesis; at a generally accepted 30% lower efficiency rate (based on reflection).
We do also know based on real world plant growth studies, white light, which is green heavy (around 50%) actually begins to slow plant growth.(Reference #5). So there's a balance to all colors needed.
Be careful about making the assumption that this means plants, especially water plants and even more so photosynthetic corals need yellow and orange light spectrums in large quantities as some online articles imply, as both extensive practical experience by many as well as the documented experiments shows this to simply not be true.
Blue has shown better growth, but yellow is still important synergy.
Even with Terrestrial plants under artificial lighting, we know that blue lights along with even more so reds are what matter for optimal efficient growth, this is demonstrated both practically and factually by the Vertical Farms link I provided earlier where 2/3 of the light is provided by the red spectrums and 1/3 by the blue and NO light from green, yellow or even orange. This is again why (as noted earlier too) why a white LED such as the AquaRay GroBeam would not be the best choice for an application such as a vertical farm since it too adds all cyan, green, yellow and orange color spectrums!
However it is noteworthy that green light does penetrate better than reds due to the higher photon frequency, but our cited references and this graph show at least 20-30% lower efficiency as well as practical experience has shown that green is less efficient and while part of photosynthesis, in amounts over 25-50% of overall light energy actually slows growth. As well it has been demonstrated that green can be only 20% as efficient as certain blue spectrums, as I will demonstrate in the next section. (Real World Applications)
We also know from both science and decades of practical experience that without the blue, corals such as acropora will not thrive.
To the left is another graph that displays most electrically efficient colors of LEDs, based on moles of photosynthetic photons per joule. These are blue, red, and cool white, respectively.
We also know that some of the earliest LED emitters and common LED emitters still used in LED flashlights tend to be in these more spectrums or type (you can see this when comparing a LED flashlight to halogen flashlight).
Another term that we should know is "Quantum Yield in Photosynthesis".
Quantum yield in photosynthesis is the moles of CO2 fixed per mole of quanta (photons) absorbed, or else the efficiency with which light is converted into fixed carbon. Typically about 0.06 moles CO2 are fixed per mole of quanta under favorable conditions (and normal (ambient) CO2 concentration).
Real World Application of RQE, PAR. PUR, PAS, & Photons:
The two pictures above make a real world application point as to the real outcome of light wave lengths.
The first picture to the left displays plant growth with three different light sources, driven at lower and higher PAR values.
It is clear from the graph that the green is 50% less efficient than the red and a whopping 80% less efficient than the blue. So this study somewhat destroys the 30% argument!
The next study, which is one that made me really start looking into LED lights more in 2007 including in my "Aquarium Lighting" article. This one obviously has a few added variables, most notably the input energy in joules of a Metal Halide is considerably higher with vastly more energy being wasted as heat energy, never going to photons of light.
However when you get down to the actual lumens of energy, the Metal Halide is still higher yet the growth rate is still considerably and very measurably lower!
Why? The only answer is the photons of light coming from the 6500K LED Grow Light (generic brand) are at a frequency more readily used by this plant, in other words a higher useful energy or PUR.
Here are a few more example based on the history of aquarium lighting which I alluded to at the beginning of the article:
- Using T12 Fluorescent lights of equal length & wattage as an example, where by lumens per watt, light spread, input energy is ALL EQUAL; when we switched from a warm white light to a trichromatic daylight T12, plant growth increased
- Again using a T12 fluorescent lamp, except this time two 20 watt cool white, when we changed to one triton and one actinic, we able to maintain some photosynthetic marine life we previously could not
- Using equal sized "aquarilux" T8 lamps (made by PennPlax), while these really made the aquarium fish and decor "pop" with color, better growth was achieved with a 6500k daylight lamp of the same size and type (T8).
What the three examples only differ on is spectrum or "PUR", all other variables were the same.
What also stands out is that while some lighting professionals might state that all "white light can grow plants", this is based on recent history. As most modern LEDs CAN grow plants since so much light energy is being delivered, there is generally enough energy to grow the plant (or corals), just not as efficiently as a more targeted single light source with a spectrum imitating the spectrum of noon-time tropical sun such as pure daylight 6500K versus blended light colors.
The above make for easy to understand examples because we were still at very marginal energy delivery with a 40 watt Trichromatic T12 light, so having an optimal spectrum was VERY noticeable where it would not be with a light that puts out copious amounts of PAR (but why still waste energy and not have the best when it it possible?)
There are many more real world examples, including those we have already provided such as the average PAR at a Coral Farm that uses sunlight and is still lower PAR than many drive their artificial lights at to maintain a healthy reef aquarium, which obviously screams out that there is more at play than just quantity of photons.
Finally, let me clear something up based on feedback; I am well aware that a photon IS A photon having a very strong science based background (as a child, I rarely read novels, but as my parents can attest to, I read the entire World Book encyclopedia set cover to cover and more than once at that).
Just as I know based on radio wave navigation being a pilot as well that a FM radio wave is line of sight while an AM wave bounces, it is basic science that the only difference between one photon of light and another is the frequency and energy level. We know that a blue light is simply a photon with a lower wave length but higher frequency and energy level than a photon of red light, but they are both photons.
Think of how an X-Ray, which is lower waver length and higher energy yet than a blue 420 nm blue photon, penetrates your body. Would a 420nm blue blue light work if you need a light that penetrates as an X-Ray does? Of course not as there IS a QUALITY of light/photons based on the application at hand!!!
Ditto how the visible blue, green, and red spectrum behave, but with much smaller differences in frequency.
Bringing this back to photosynthesis, photosynthetic plants and alga respond differently to these varied frequencies of each photon, with water adding to the equation since shorter wave lengths penetrate more readily with a given energy level. This is where we get our useful light energy term from, as do know (as graphically demonstrated above) that certain photo frequencies react differently and thus are likely used differently by photosynthetic life forms. It is noteworthy that while we can certainly make generalizations, we know aquatic life, especially marine life have adapted/evolved to utilized the type of light most common in their environment, which we in turn need to duplicate as best as possible with our still feeble when compared to the sun man-made lights!
Also do not let the use lower higher energy/frequency of blue light confuse you that blue light would equal more photons, as it would not. This is determined by the amount of input energy. As even a higher input energy (in joules) of red light will penetrate deeper than a small input of the same red light. Think of a flashlight that has its batteries mostly worn down versus when new, you can easily see how the newer battery light cut through dark moonless night.
Spectrograms or spectrographs are often used to determine PUR (Useful Light Energy), however I have found these are not fool proof either.
Although when it comes to many of the LED Aquarium Lights now flooding the market, Spectrograms are often very difficult to come by.
Part of the reason in my opinion and from knowing many in the industry is that the development of new LED emitters and drivers to run the emitters is at a fast pace, while the cost of producing a spectrograph for such a narrow band of users is simply too cost prohibitive (aquarium use of just the better LED emitter bins is but a needle in a haystack in the high end LED emitter industry). The other part of the reason is a bit more deceptive and that is many simply are VERY lacking in essential PUR!
However there are both good and bad LED fixtures with either new spectrographs available or outdated spectrographs. As well while spectrographs are useful, these too do NOT show the whole PUR story anymore than a PAR meter accurately depicts the type of light energy delivered (especially in the blues).
However taken together (PUR Spectrograph and PAR reading), a more complete picture can be extrapolated where the mmol (µMol•m²•sec) reading of a PAR Meter can be combined with the spectrograph of actual specific light energy wavelengths.
If a spectrograph is equal, PAR comparisons can be more accurate too!!
Here are a couple of spectrograms we produced;
*The first to the left displays 12 different spectrograms for singular emitter types, (no mixed emitters).
The light energy spectrograph of the high output 4.5 volt DC LED flashlight is interesting, as it displays a reasonably good spectrograph. HOWEVER the output of actual energy (in wattage and PAR mmol) is obviously much lower than the 3 watt XR, XG, XT, ML, & XB Cree emitters as well as the cutting edge Osram Olson NP Blue emitter.
Similar can be said about the 3 watts input spread over the entire TMC Flexi Red (spread over 18 inches) and similar LED Strips.
Which is why neither of these are nearly as much of a factor in your aquarium lighting scheme for higher light requiring planted or reef aquariums. This is not to say the Flexi-Red cannot add some "Useful Light Energy" (especially in the near-infrared) as a compliment to say a GroBeam or similar high output LED Fixture.
In the end, input energy must be considered, and of course PAR is most certainly an important measurement still since we would clearly find that the flashlight has a much lower PAR than any light using the higher power Cree emitters & others commonly used in most aquarium LED fixtures.
The picture above can be clicked on to enlarge
To make clear as per Spectrograms/spectrographs, as I noted earlier, these are not fool proof since there are aspects we do not fully understand including the possible synergetic affect of certain combined spectrums.
Real world examples of where we need to be careful would include my extensive experience, albeit anecdotal, with fluorescent lights. One such extensive experience is the use of Triton 6500 K T12 lights versus other brands. They all had an equal 40 watts input energy and similar spectrographs, yet the difference in plant growth was quite noticeable.
EXAMPLES; (Admittedly over simplified for better understanding) These are assuming a 30% lower green efficiency, which is being generous based on proven real world studies that show lower green efficiency of closer to 50-80%, if these studies are taken into account, the differences are more dramatic:
*Exhibit ONE that measures a 150 PAR reading at 12 inches
*Exhibit TWO that measures a 120 PAR reading at 12 inches
However Exhibit ONE produces 50% of its energy in the less efficient green to yellow spectrum (assuming 30% less based on RQE) and the other 50% in the photosynthetic active range while exhibit TWO produces 90% of its energy in the exact spikes of the photosynthetic active range.
So with the math, this brings down exhibit ONE to essentially 118 efficient/useful PAR while exhibit TWO is at 128 useful light energy PAR.
Obviously what appeared to be the much more inferior light is much closer. If now driven with optimal drivers & PWM, (often requiring cooling fans) the 120 PAR might be the better choice for light efficiency since it will likely require much less input energy for output of useful/efficient PAR!!
As a more extreme analogy, which no Aquarium LED light employs, so I'm using it only to make a point:
*Exhibit ONE that measures a 150 PAR reading at 12 inches using ONLY green emitters
*Exhibit TWO that measures a 120 PAR reading at 12 inches producing 90% of its energy in the exact spikes of the photosynthetic active range
In this fictitious comparison (since no light uses only green emitters), Exhibit ONE produces 105 PAR, and is not not only less energy efficient, but also produces less actual usable PAR.
Hopefully this fictitious comparison drives home the point that one can have a high PAR, but lower PUR & PAS.
A good example is the EcoTech Radion (with off the shelf, but still excellent Cree XT-E & XG-E emitters) and AI Sol, versus the AquaBeam Reef White NP 2000 Ultima, which does not have as high a PAR reading, but their PUR is higher per wattage used due to more specific patented emitter bins, PWM, and better drivers (constant current drivers versus RGB control features). It is also noteworthy that the AquaRay 2000 NP as well as the 1500 utilizes the unique Osram Olson NP Blue Emitter which actually is a FULL PUR/PAR Spectrum light, not just blue.
While the EcoTech Radio Pro produces 1100 µMol•m²•sec PAR (at 6" as per EcoTech's published information), the TMC NP 2000 produces 380 µMol•m²•sec (at 15" as per TMC's published information).
The input wattage is 170 watts for the EcoTech and 30 watts for the AquaRay, therefore is takes about (5) AquaRay 2000s to equal the wattage used of the EcoTech Pro, which then equals 1900 µMol•m²•sec PAR for the AquaRay. ABOUT DOUBLE (and likely more than double since the AquaRay published numbers are at more than twice the depth for PAR measurements)!!
The above example means that it takes DOUBLE the input energy for the EcoTech to equal the AquaRay, ASSUMING the spectrographs are equal, which in the case of the EcoTech Radion Pro it is quite similar but for wasted energy with the NUV emitters used, unlike the AquaRay 1500 & 2000. This can also be said of some of the lessor brands too, such as the Taotronic, Ocean Revive, Evergrow, etc.
Why the difference?
Simply less efficient emitters, a not as good a choice of emitter, and certainly a LOT of wasted energy as heat.
This is not to say the EcoTech Radion (or others) cannot keep Reef life, but these have more wasted energy as a percentage energy wattage input then the light energy output.
Please see the graph in this article below which clearly displays the difference in PUR between emitters:
Aquarium Lighting; PUR including Graph
Before I seem to pick on the EcoTech, let me perform a comparison of the EcoTech Radion Pro versus the Evergrow LED. assuming PAR and wattage used are the same, but use the VERY IMPORTANT PUR Spectrograph to determine light quality.
Using the Evergrow (AKA Ocean Revive) as a comparison, and since this company does not publish a spectrograph (for obvious reasons in my opinion), I will compare emitters used to the superior EcoTech.
Since it is well established that the warm white emitters used are inferior as per the graph in the above cited reference, we can safely assume the Evergrow has a lessor spectrograph than the EcoTech.
So say both produced 500 µMol•m²•sec at 15", would both lights be equal?
The simple answer is NO!!
The Ecotech would be superior, as when if all parameters are equal, including PAR readings, the PUR is going to trump the PAR. This is why PAR reading should only be taken as the starting point and PUR should ALWAYS be considered in the mix since as it is the "photostynthetically USEFUL Radiation".
What a reef keeper who is considering one of the many LED lights now available should consider, especially the Chinese brands such as TaoTronics or Evergrow, as per the "scientific numbers", which again relates to PUR versus PAR is the emitters used in terms of wattage draw and PUR output per intended application.
Couple this with the fact that with the other less than optimal bridgelux emitters, use of current reduction technology; One requires a 120 watt LED fixture for the Evergrow, Taotronics, and many similar LEDs to even questionably have the same output in "quality" photons as say an AquaRay Reef White 2000 Ultima at 30 watts of energy consumed or two BML 14000K Reef Spectrums of a combined 32 watts energy consumed so as to keep reef life.
One then has to ask why bother replacing your Metal Halides of 150 watts just to save 30 watts of energy, not to mention the high heat output that may still require chillers, and in the end the need for cooling fans for current reduction technology that has resulted in fan break downs and even fires????
Another aspect of PUR which is noteworthy is popular use of RGB features where by the user can control the color output of the lights.
The problem with this feature is when one alters the colors, you also alter the spectral output.
This may not affect PAR, but it MOST CERTAINLY affects PUR!!
These features should be avoided unless being used as a decorative light. I would not recommend these features for a serious reef or planted freshwater aquarium keeper.
(Please click picture to enlarge)
Depth Penetration is another consideration when choosing lighting. This is where the Metal Halide used to "control the market".
However modern LEDs have closed this gap considerably with lights such as the AI Sol Vega Blue, Kessil, and the TMC AquaRay Fiji Blue, Reef Blue, 2000 Reef White, and Ocean Blue NP Ultima, among others high end LEDs intended for reef aquariums.
The blue spectrums are more important to many light sensitive corals for the Phototropic response aspect of PAR, in part since these corals, clams, etc. live in environments where little higher spectrums of light reaches these corals.
In an aquarium this becomes more important in depths much over 20-24 inches, depending upon the light used including its raw energy.
Even here consider what is used.
In the picture above where a sheet of computer paper is used to block light energy, you can see how the Fiji Blue with its unlensed XT-E emitters has a more deeper blue (down to about 420nm) light which generally would penetrate better than a higher nanometer color light.
However the Reef Blue with its more focused ML-E royal blue emitters has more depth penetration as shown in this picture.
For this reason, while the Fiji Blue might seem like the better choice for tanks over 24 inches in depth, this picture very simply shows this to not be correct.
This is not to say the Fiji Blue or similar violet emitters used by a few LED fixture are a poor choice, only that using focused emitters can also make a difference.
In fact, lights such as the Violet/Fiji Blue LED are useful in providing specific wavelengths many corals might require, my point is simply do not purchase these for optimum depth penetration.
Also sometimes a mix of "blues" such as in the EcoTech Radion can make a difference in depth penetration.
The "Reef White 2000HD Ultima NP" or "Ocean Blue NP Ultima" also includes the Osram Olson new "NP blue emitters" in their mix.
This is also where the new Osram Olson NP (Nature Perfect) Blue emitter excels since these are the first emitters designed specifically for reef aquarium life.
Basically these are a FULL SPECTRUM "Blue" LED emitter (see the spectrograph below)
Now using the AI Sol Vega Blue as an example, it uses uses (4) Cree XM-L Cool White LEDs, (8) Cree XP-E Royal Blue LEDs, (4) Cree XP-E Blue LEDs, and (4) OSRAM OSLON Standard Deep Blue LEDs.
This is a good depth penetration light if only by virtue of the many blue emitters used and proprietary 40 and 70 degree lenses, however it does fall short in that it uses older bin low depth penetrating cool white and the standard XP emitters are not intended as a depth penetrating emitter (unlike the XR-E and even newer ML-E Blue). As well this light uses RBG features and Current Reduction, rather than PWM which further lowers PUR and wastes energy as heat instead of light energy.
Reference: Aquarium Lighting; PWM
Hopefully readers come away after reading this article and its many cited resources with a better understanding of PUR/quality of light, not that I am stating certain LEDs or other lights in particular CANNOT keep photosynthetic life.
As well I am NOT stating that if a fixture uses green emitters it is a poor light.
While green light has some proven applications in a closed environmentfor more growth when under 24% of overall light spectrum as well as producing a more pleasing overall light when part of the spectrum. However a fixture that is heavier in the green spectrums is going to be less efficient for photosynthetic growth and possibly detrimental when over 25% of the overall spectrum as per cited .edu references.
I will also add that one has to look at the preponderance of evidence, both from .edu websites, NOVA, and similar sources as well as practical experiments and use COMMON SENSE that if one theoretical article comes to different conclusions, but the preponderance says otherwise, that we need to go with what in the end the majority of evidence states (not that what a contradictory relative quantum efficiency graph states that does not agree with other evidence and experiments such as cited at Reference #5).
We also need to understand that all these studies using different light spectrums for growth, including green, that these are in closed & controlled environments (which of course are aquariums are closed environments).
However in nature it has long been established, including in an episode of NOVA (PBS science series) that green light in the open environment of nature is generally not used.
So in the end, when one forces their plants or coral to utilize green light, we can make this analogy: "You ran out of your quality fish food, so instead you feed your fish soda crackers". While not a perfect analogy, it still makes a good point in that you are forcing the specimen whether it be a plant, coral, or fish to survive on less than optimal "nutrition"
Part of my goal in writing this article is also pointing out that those who might have large DIY or other 220 watt LED panels with cool white, green, yellow emitters, etc. along with fans blowing away wasted energy as heat might have an excellent light system, just not an energy efficient system (the vertical farms further prove this).
HOWEVER it is simply a LIE for these same aquarium keepers to say a light system using higher PUR LED lights such as say three AAP AquaRay 30 watt tiles on a similar aquarium can only keep maybe "softies" or require more lights for high light planted aquariums, the FACTS presented here along with the many references prove otherwise.
Using the growing Vertical Farm industry as an example again (Reference #6); they are attempting to get the most light for their energy input, which translates into profit. As someone going into the market to purchase asparagus could care less how the lights look on the asparagus, only that if a light using more middle spectrum light energy and wasting energy as heat is going to product asparagus that cost more!!
Now we as aquarium keepers DO care how our lights look, but with better spectrum control that focuses on "photosynthetic action spectrum" but still allows for full spectrum light we can have a nice balance of efficiency and light (which I have already shown with many high efficiency spectrograms) that presents our corals and plants well.
As well as to naysayers who say one cannot compare a vertical farm to freshwater aquarium plant keeping or the zooanthellic algae found in corals, I say NOT true!
While there are certainly differences including requiring more blues for deeper water specimens, there is still MUCH MORE in common than there are differences!
A common argument by many is that we do not know the specifics of individual plant or coral active photosynthetic light requirements, while this may be partly true, we do know enough.
What is hypocritical of these persons, is that they will use T5 lights designed for planted aquariums or reef aquariums. However the simple fact is these lights are more targeted than a warm white T12 fluorescent light one would purchase at Home Depot, YET I have kept lush planted aquariums back in the 1970s over aquariums with multiples of these shop lights.
So why do these same persons not just go ahead and use these T12 lights? We know the answer as they have already made the point of this article by using a modern aquarium specific T5 or T2 over a warm white or cool white T12 shop light!!!!
A silly but practical analogy to such arguments is to warn persons of a low doorway that is only 5 feet tall, then to have someone come and say this warning is not accurate because there are people under 5 feet tall. While this may be true, the majority of the adult population is well over 5 feet tall, and to write off this warning as not credible just because a small percentage is not of this height is silly. Ditto these arguments of what we know about useful light energy for photosynthesis!
Another argument used to attack the science of PUR is that we can over saturate the plant or coral we are lighting by using targeted wave lengths.
This is nothing more than a "Red Herring" argument (being put out by a disrespectful employee/salesperson of a LED seller that should never have employed such a person).
The problem with this argument is we are no where near any light saturation with man made lighting. Let's apply common sense logic hear when dealing with such ludicrous arguments; if this were so, why is it we cannot go out in a boat on a reef at night with our most powerful metal halide lights and even come close to lighting to the depths and saturation the sun would provide in this same area during daylight hours??
Come on people, when persons such as this young lady come up with such ludicrous red herring arguments and refuse to do her homework and instead make disrespectful personal attacks on persons such as myself, you need to walk away!
One more argument is based more on theory using green algae such as Codium fragile and Ulva pertusa that contain a keto-carotenoid, siphonaxanthin, which absorbs green light with a peak at 535 nm. While these "black" more than green algae can utilize green light well, this does not transfer over to most zooxanthellae living corals or aquatic plants grown by planted freshwater keepers (unless growing blackbeard algae is your goal, which increased green light will certainly help you here!!!).
In the end, most modern LED aquarium light fixtures with only a few very low end exceptions can keep the aquatic life they were designed to, whether planted aquariums or reef aquariums.
What it really no comes down to is efficiency, and a light with a higher PUR (quality of light) is going be more efficient and require less input energy all other aspects being equal.
The interesting fact is most other aspects are NOT equal outside of being able to keep the designated aquatic life as most aquarium LEDs have poor warranties as low as 180 days and even those with better warranties still are only for repair, not full light replacement.
Also MOST all do not have the important IP rating for water resistance/proofing (IP67) resulting in a light an electronic lighting device (LED light) that has a poor warranty and less than optimum resistance to water.<.p>
As per my biases here, which are obvious. Of course I have a bias, why would I not recommend what my years in the hobby/industry (1968/1978) and research points to be one of the best (note I am not saying THE best either, as there are too many subtleties for which no company makes the best light for everyone)!?
Such "Ad Hominem" attacks accusing me of bias thus discreditig me are akin this example;
PERSON 1: “I think Volvos are fine automobiles.”
PERSON 2: “Of course you’d say that; you’re from Sweden.”
Reference: Logical Fallacies
Just make you put on your thinking cap before you purchase and fall for the hype. Once everything is factored in, including a FULL understanding of PUR & PAR, all the bells & whistles in the world or even a low initial price does not help when you have a failed light in a couple years with a non existent or poor warranty since most aquarium LEDs do not have the optimum waterproof rating of IP67 or higher best suited to placing what is basically an electronic light emitting device over water!
Also use your math thinking cap to realize that not only do these bells and whistles and other gimmicks cost money, but so does the sponsoring of aquarium forums and many other events, this money does not fall out of the sky and comes out of the quality of the product!
(1)Aquarium Lighting; Facts & Information
(2)PUR and Reef Aquarium Lighting: What is PUR? By Captive Aquatics
From this above cited article:
"For example: you are given a choice to illuminate your coral with two different lights, each with the same PAR value. However, one of these lights produces energy that peaks at 450nm, or the blue spectrum, and one peaks at 590nm, or the yellow spectrum. For zooxanthellae in your coral's tissue, the light peaking at 450nm will have greater PUR than the light that peaks at 590nm, although the PAR numbers are the same."
(5)Plant Productivity in Response to LED Lighting
(6)PPFD — A Grower’s Best Friend (use of specific high PUR/PAS emitters)
(7)Green Light Drives Leaf Photosynthesis More Efficiently than Red Light in Strong White Light: Revisiting the Enigmatic Question of Why Leaves are Green
Here is some of the THEORY postulated in this article: "If leaves of land plants had black chloroplasts with siphonaxanthin, the leaves could close the so-called ‘green window’ and increase their absorptance"
(8)Physical Properties of Water
(9)Small Polyp Stony Coral and Light Wavelengths
(10)Economic Analysis of Greenhouse Lighting: Light Emitting Diodes vs. High Intensity Discharge Fixtures
An interesting study, but is more of a laboratory type study rather than a real world study (unlike the real world study in the CBS article I quoted earlier). I think this quote is more subjective than real world objective: "HPS lamps are equal to or better than the best LED fixtures because they have a high photon output near 600 nm and a low output of blue, cyan, and green light". As we know for both real world acropora and horticultural use, that blue light energy is still necessary and in fact is an efficient LED light source.
(11)Action spectrum; Wikipedia
From Wikipedia: "An action spectrum is the rate of a physiological activity plotted against wavelength of light. It shows which wavelength of light is most effectively used in a specific chemical reaction. Some reactants are able to use specific wavelengths of light more effectively to complete their reactions. For example, chlorophyll is much more efficient at using the red and blue spectrums of light to carry out photosynthesis. Therefore, the action spectrum graph would show spikes above the wavelengths representing the colors red and blue."
(12)Photosynthetically active radiation (PAR); Wikipedia
NEW, From this website:
(13)Lighting Requirements of a Planted Aquarium- RQE, PFY, PAS, & PUR
(14)Wavelength Influence on Plants
An excellent unbiased look at light colors and the importance of each
(15)Green light: Is it important for plant growth?
(16)Influence of Green, Red and Blue Light Emitting Diodes on Multiprotein Complex Proteins and Photosynthetic Activity under Different Light Intensities in Lettuce Leaves
From the above cited .edu article:
"Chlorophyll a absorbs its energy from the Violet-Blue and Reddish orange-Red wavelengths, and little from the intermediate (Green-Yellow-Orange) wavelengths"
(18) Photosynthesis; Wikipedia
(19) PUR or RQE, YouTube Video Fail- Guide to lighting a planted tank
(20) PPFD — A Grower’s Best Friend
Recommended Aquarium Light Product Resources:
*Aquarium LED Light Fixtures; AquaRay
*T2 Planted/Refugium Aquarium Lights, Lighting
*SHO Planted Aquarium and Refugium Lights, Lighting
Forum Thread about the importance of a IP67 Water Proof rating which MOST aquarium LEDs do not have including the popular brands such as Finnex:
Waterproof LEDs (from Everything Aquatic)
By Carl Strohmeyer-PAMR & Steven Wright
Other Recommended Reference & Product Sites
PUR or RQE, YouTube Video Fail- Guide to lighting a planted tank
EcoTech Radion Pro Versus AquaRay LED Lights
A MUST read article/review for any truly serious marine reef keeper looking to get the best LED lights based on science and NOT purchase based on hype and good marketing
Saltwater Aquarium Information; Basic to Advanced
Aquarium or Pond UV Sterilization
Premium Tropic Marin Pro Reef Sea Salt from Germany
There is simply NO BETTER Reef Sea Salt (marine fish too)
TMC Premium Fluidized Sand Bed Bio Filters
Premium, second to NONE Aquarium Bio Filters, that with Oolitic Sand also maintain essential marine aquarium calcium levels, alkalinity, & electrolytes that are important to ALL Marine life, Goldfish, African Cichlids, Livebearers & more
San Francisco Bay Brand Seaweed Salad
"Seaweed Salad" is much more nutritious than spinach and lettuce. This product is recommended for all saltwater Damsels, Clownfish, and especially Marine Angels and Tangs
Hanna Instruments Aquarium Testers & Meters; For Freshwater and Saltwater
Hanna instruments is a global manufacturer of analytical instrumentation. Hanna offers multi-parameter bench top portable meters and testers..
*Aquarium Ich; Identification, Treatment, Prevention
Hydor Smart Wave Controller
• Promotes a healthy reef aquarium or similar aquarium environment where wave action is desired by recreating natural currents found in nature
• Synchronous program for currents typical of barrier reefs and alternate for tides
TMC Advanced Venturi Saltwater Protein Skimmers
A High performance, quality protein skimmer incorporating a patented venturi injection system which optimizes the perfect mixture of fine air bubbles and water and ensures intensive, efficient skimming and the removal of proteins and other harmful toxins (waste) from the aquarium.
For a friendly, Knowledgeable, aquarium forum with in a family atmosphere:
*Aquarium Forum; Everything Aquatic
Non Stop Air Pump, AC OR DC
This air pump pushes out 4L of air per minute, REGARDLESS of whether you have AC power or NOT