Tag Archives: lighting

Photosynthesis and PAR; Planted & Reef Aquarium

These are important aspects of both high end freshwater plant keeping and symbiotic Zooanthellae living within Photosynthetic invertebrates.

By Steve Allen

Revised 1/8/19

I will discuss each of these related aspects of Aquarium Lighting in a little more detail:


Photosynthesis, Aquarium, ReefPhotosynthesis is the synthesizing by organisms of organic chemical compounds, mainly carbohydrates, from carbon dioxide using energy obtained from light rather than the oxidation of chemical compounds.
Put another way, this means photosynthetic plants, algae, and similar use of energy obtained from light to produce cellular chemical energy and carbohydrates when combined with carbon dioxide necessary for life processes including nitrogen processing for growth.
Further Reference: Aquarium Nitrogen Cycle, Cycling

In order for the photosynthetic process to take, the organelle of the cell where light the energy to chemical energy takes place (named the chloroplast), must receive sufficient PAR (photosynthetic active radiation).
Often in aquarium environments the compensation/saturation point is not met within the chloroplast, this results in the organelle not producing the optimum amount of carbon bi-products (carbohydrates), and this excess energy will not be transferred to the host Photosynthetic Invertebrate..
The other side of the coin (more common in the ocean, tropical rivers, etc.) is photinhibition, which is the result of an excess of light energy causing cessation of photosynthesis altogether. Photosynthetic invertebrates as well as many higher plants have many light inhibiting pigments to protect themselves from tissue damage caused by photinhibition (hence the green and other colors that are often more vivid in higher light).

A myth of reef aquarium keeping is that Photosynthetic invertebrates such as corals only need the “correct” light to survive, however this is incorrect as no known animal can survive solely on light energy as there must always be a source nitrogen and other minerals for growth and reproduction.

PAR (Photosynthetic Active Radiation);

PAR, photosynthetic active radiation diagramPAR is the abbreviation for Photosynthetically Active Radiation which is the spectral range of solar light from 400 to 700 nanometers (some resources/research indicates up to 750n) that is needed by higher plants & symbiotic zooanthellic algae.
This is found from actinic UVA to near infrared. UVA is the bandwidth found between 400-550nm which is the absorption bandwidth of chlorophylls a, c², and peridinin (the light-harvesting carotenoid, a pigment related to chlorophyll).
For our discussion of PAR, near Infrared is defined as the bandwidth found between 620-750nm which is the red absorption bandwidth of chlorophylls a and c² (true infrared is beyond 750nm).

Light sources that emit mostly actinic light will often have a lower PAR (although actinic Violet-blue still occupies an spike in PAR as seen from the graph and improve the PAR of your lighting), bulbs that occupy mostly the middle spectrum (yellow-green) such as “warm White (2700K) will produce little necessary “Useful Energy” spikes (PUR) within PAR, while bulbs that produce UVA and yet more infrared will produce more important PAR light energy (as seen from the graph which shows the UVA spike and two infrared spike required for PAR).

It is noteworthy that most symbiotic zooanthellic have evolved/adapted to the lower blues of the Ocean Reefs need more of the blue/actinic spike than “higher plants”, hence the popularity of actinic lights for reef aquariums (this is true of other green algae).
However the optimum nanometer range is about 465-485nm (with some corals requiring more 420 as well), not the ONLY the lower 420nm many actinic lights produce or the more broad range many “blue” aquarium lights produce of 400-520 nm. This is where the latest technology LED lights “shine”, having a more precise 465-485nm blue as well as the lower actinic blue found in the Fiji Blue LED.
For this reason it is a good idea to have extra actinic for corals/clams that depend upon zooanthellic algae, while at the same time limiting blue/actinic in freshwater aquariums to avoid excessive green algae growth.

With he above in mind, the addition of lights that product more near infrared light spikes or the use red LED emitters does not help most photosynthetic corals and in fact some studies indicate to much red light can hinder acropora growth.
This of leaves me scratching my head why one oddly popular Aquarium Reef LED manufacturer adds red emitters to their LED fixtures (& worse, green emitters)?

Source: AquaRay LED Aquarium Lights, Lighting; Including Fiji Blue

PAR is the simplest, albeit not the most accurate way to measure light energy and quantity for the home/office/commercial aquarium. PAR is more simple to define and measure than any other forms of light measurement. However it is noteworthy that PUR is the much more important measure for saltwater reef aquariums.
The facts are you can have a light with a higher PAR be a considerably lesser PUR and thus inferior light.
Important Reference: Why PUR is more important in reef aquariums

For the aquarium keepers purpose, PAR is the number of photons per meter squared per second of light that falls between 400 nm and 700 nm in wavelength with the better PAR meters measuring the important spikes.
The meter displays these numbers in µMol•m²•sec (“mmols”), with currently accepted numbers measured as µMol•m²•sec at 50 mmol for most plants or low light corals such as Nemezophyllia, while Acropra can require PAR outputs as high as 300 mmol (any higher is simply a waste of energy/light)


To bring this concept of PAR vs. PUR to live for a real world example is a high end LED fixture compared to low grade (low PUR) fixture. Two fixtures could have the same PAR, but one could have a higher PUR. Like I’ve said in other lighting articles before…Just like there are multiple ways to add up to 10 (5+5 or 2+8), both will give you the same appearance, but one might be more beneficial to the overall tanks needs.

I strongly recommend taking a look at this additional article to help understand this concept more. It’s a shorter read, but if you digest the information in the post, it will help make this a concert idea.

PUR, PAS, PAR in Aquarium Reef/Planted Lighting; LED Wavelengths

PAR vs PUR AquaRay Readings

PAR vs PUR AquaRay PAR reading

Here is a quote from a professional in the aquarium industry that grows only SPS Acropora Coral. The hardest in the world…

Around 150 (PAR) at the sand and I could keep clams, grow sticks or anything on the sand…

This professional was not taking into account PUR, but was proving that most of what we can put to our aquariums can be grown with a lower PAR. Having a high PUR fixture will only enhance the growth of the coral or plants. A cheaper LED could have a higher PAR, but not allow for corals or plants to thrive as much as a higher PUR fixture. In this case, more PAR is required to make up the lack of PUR.

Remember: PAR varies fixture to fixture and all depends on the tech. used, mounting height, and spread. A PAR meter can be used, but it is just a tool and does not show the whole picture. It leaves out the important concept of PUR.

References; Further Reading/Information:

*Aquarium Lighting; Facts & Information

*PUR vs PAR in Aquarium Lighting; why PUR is more important in reef aquariums

*Reef Hobbyist Magazine; Understanding Lighting and Photosynthesis
3rd Quarter 2010, By Mike Maddox

Copyright 2019, By Steve Allen


AQUARIUM LIGHTING BASICS; Parameters, Lights Technology

By Steve Allen

Further Revised 1/5/19

Much of the information used with permission from:
Aquarium Light- Facts & Information

Sections Included in this Article:

Aquarium Lighting Overview

Aquarium Light Typs, Metal Halide, LED, CFL, T2, T5, SHO
There are many considerations when choosing aquarium lighting, in particular lighting for “high end” applications such as marine reefs or high light planted aquariums.

“Watts per gallon” is still often referred to, however of late this is but one part of many parameters to consider.
This is specially true when high end LED lights are considered (this does not include low end and similar LED lights).

An example of a “high end” LED:
TMC AquaRay Aquarium Light Systems

An example of a “low end” LED:
Marineland Double Bright LEDs

Watts per gallon is only useful in comparing “apples to apples” such as similar T5 lights to another or related technology LED lights to another (not a Marineland Double Bright to a high end TMC AquaRay LED).

For a better understanding please read this ENTIRE Aquarium Lighting article, which explains that a watt is simply a measurement of input energy, NOT light output either quality or quantity:
Aquarium Lighting Information

Even comparable lumen output of the lamp is no longer a good measure of lighting parameter performance due to focus and restrike as well as PAR & related useful light energy (PUR).

A good example is a modern LED such as the AquaRay which has a vastly higher useful energy (PUR) output than a comparable wattage CFL (such as a Current USA Compact Fluorescent) at 20 inches.

Important Parameters to consider when choosing a light for your aquarium with the first two probably the most important [not a complete list]:

  • Photosynthetic Active Radiation- PAR
  • 20-40 PAR required for high light demanding plants, including all photosynthetic carpeting.
    One way to look at PAR is the quantity of light photons

  • PUR/Useful Light Energy- this is an IMPORTANT FACTOR as per currently known & proven science, and when PAR of two different lights is equal, then PUR will trump PAR. But unfortunately this is also a very difficult parameter to measure.
    One way to look at PUR is the quality of light photons.

  • Watts per gallon
  • Lumens and lumens per watt
  • Output in relation to bulb length (this is where LEDs and to a lesser extent T2s and T5s excel).
    While a minor parameter, it is still worth considering
  • Lumen focus (AKA Restrike).
    This is common to ALL fluorescent lights, whether modern T2 or T5 or older T12s.
  • Lux is derived from the lumen and is a measure of illuminance.
    This is the luminous flux hitting the surface.
    Similar to PAR & PUR as this is the amount of useable light.

    For example, 1000 lumens spread over an area of 1 square meter gives you a figure of 1000 lux, however the same amount of light spread over 10 square meters gives an illuminance of only 100 lux.

    In short illuminance is more relevant to lighting an aquarium than luminous flux (lumens), because this is the measure of light that can be applied to your aquarium.

    This figure will decrease the further from the light source you get.

As an example of the inaccuracy of the watts per gallon so-called rule, please consider these comparisons for an assumed 20 gallon aquarium using High End LED Lights (GroBeam) and T8 or T12 Fluorescent lights such as the Flora Grow (by Hagen):

* 20 watt T12 light with a Kelvin temperature of 5000 K
Compared to:
*20 Watt LED with an adjusted Kelvin temperature of 6500 K

The “watts per gallon rule” would certainly require at least four of the 20 Watt T8/T12 Flora Grow while this same 20 gallon freshwater aquarium would only require ONE 12 watt TMC GroBeam 600 LEDs, this is .15 of the required wattage or about .60 Watts per gallon!!!

For reef applications using high end LED emitters only, not Marineland Single/Double Bright, Ecoxtic Stunners, etc., It’s suggested for about .8 to 1 watt per gallon. So, two AquaBeam Reef White LEDs would be my suggestion for this 20 gallon aquarium.

Based on raw data from controlled tests, even the modern comparable Kelvin HO T5 lights or Metal Halide, which are so popular do not hold-up in comparison to a modern LED with the latest generation LED emitters used by AquaRay and a handful of others. This data indicates a modern LED requires 14-28% of wattage for the same useful light energy output.

Even then a T5 or even more so a T2 are vastly superior to the older style aquarium fluorescent lights when all criteria are applied (SHO as well are also superior).
Source: T2 Aquarium Lighting, Lights

Bluntly, the new generation Osram Oslon & Cree Power LED emitters, coupled advanced drivers, and Pulse Width Modulations controlling, ARE THE HIGHEST OUTPUT AQUARIUM LIGHTS PER WATT CONSUMED!
See this article I wrote for more about “Pulse Width Modulation”:
Aquarium LED Lighting, PWM

Changing bulbs:
With the exception of LED, most aquarium bulbs go through what is called a half life whereby they are at 50% output. This generally happens around 6 to 9 months in time with normal usage, however with lower usage (say 8-12 hours per day) this can be stretched to 12 months plus.

Lighting Time
Here’s a summary of lighting requirements for different aquarium types. I recommend timers for any aquarium to provide good daylight/night cycles, however this is even more important with Planted Freshwater and Saltwater Reef or Nano Reef tanks. Turn the blue/actinic lights on about one to 1/2 hour ahead of the daylight bulbs and one to 1/2 hour later in the evening.

I generally have the strongest lights on for about 12 hours per day. Sometimes with MH, I will have them in a third cycle, which is on for only about 10 hours or less. I would run moonlights for about 14-16 hours (some prefer to run these 24/7, however I have yet to find any benefit from this, other than aesthetics.

Determining what Lighting your aquarium will need

The type and intensity of lighting in an aquarium affects health, stress, coloration, photosynthesis, and stimulates reproduction. This applies primarily to aquarium plants, reef corals, anemones, etc. HOWEVER this can apply to fish too such as stress from too little light of the best daylight spectrums or too much light.

Some aquarium organisms come from shaded regions, like rain forest rivers, where most of the light in their day is indirect.

An example would be Discus which are often placed in brightly lit planted aquariums where no consideration for ‘shade’ is provided. In such tanks uneven lighting would be best.
This same concept applies to mushroom anemones, which do not require bright high intensity lighting, so if kept with acropora corals, shading has to be considered.

Choosing Aquarium Lights, Types:

Since many aquarium keepers have requested guide to sizing the light desired to their aquarium needs, I will provide a generalized “watts per gallon” at the end of three of these newer technology lights.

LED Aquarium Lights
LED Light technology has come a long way in recent years (2011 as of this update), however many are still very confused as to what a LED can or cannot do for your aquarium.

Most cheap LEDs such as the Marineland Double or Single Bright (or even those with high output emitters) do not have the correct/best PAR, and most importantly PUR (PUR trumps PAR and is the most important parameter, yet the most difficult to measure).

With the development of a few advanced LED lights such as the “high end” AquaRay LED Reef & Freshwater Aquarium Lights, the use of LED lights for high end applications such as reef or planted aquariums has become a reality in recent years..

With these low input/high output TMC AquaRay LEDs (and a few others), there is no requirement for additional/supplemental even for high light requiring planted freshwater or reef aquariums with SPS Coral (under 30 inches in depth).

As well, an advanced LED light provides healthy high quality light for a fish only tank and uses almost no electricity when compared to traditional aquarium lighting.

Watts Per Gallon: As a generalization and this ONLY applies to high output LEDs mentioned here, which utilize these technologies:

  • Latest patented emitters, such as by Cree XBs (most fixtures do not have patents) as well as the Osram Oslon NP Blue, which is the first emitter specifically designed for reef use.
  • Pulse Width Modulation Technology, NOT 0-10v “current reduction” technology, which most LEDs utilize and wastes considerable electrical energy as heat.
  • Not high amounts of green, yellow, cool white, warm white emitters
  • And drivers, which correctly regulate voltage over each emitters, since these are NOT bulbs that can be daisy chained together, rather electronic diodes requiring very exacting voltage

*For a high light requiring planted aquarium: .6 watt per gallon.
*For an advanced Marine Reef: .8 to 1 watt per gallon

Here are the suggested watts per gallon for three other top aquarium LEDs:
*1.25 to 1.5 watts per gallon for the AI Hydra & Sol LED, EcoTech Radion, and the Kessil LED

Here are the suggested watts per gallon for a few other GOOD aquarium LEDs:
*2- 2.25 watts per gallon for Taotronics, Ocean Revive, Evergrow and similar relatively quality Chinese LEDs

Here are the suggested watts per gallon for a few other lower end aquarium LEDs:
*2.75-4 watts per gallon for the Marine Double Bright, Sky, Finnex, Fluval, and similar low end Chinese LEDs

T2 Aquarium Lights
(Pictured at the top of this article)
These are probably the second newest lighting development (as of writing this article update). Similar to the T5, but with a higher yet lumen per watt output in even less space.

Although not available in as many sizes and wattage outputs as the T5 (making it not always the best fit as compared to its older technology cousin), it makes up for this in its simple diversity, which allows for linking multiple lights together for larger tanks or higher output.

The T2 aquarium fixture has another feature most T5 lights do not have; a directional lens which allows for better directional light control. This equates to better focused lumens, which is especially useful for planted aquariums or small reef tanks (not as necessary for fish only tanks).

The T2 is an excellent cost saving compliment to LED lights for basic reef or high light planted freshwater tanks (the T2 is best “supplemented” for the highest light need tanks); while for all other tanks the T2 can be used as a stand alone low operating cost light.
Even when compared to low technology LEDs such as the Marineland Single Bright, a 13 Watt T2 actually out produces the Marineland Single Bright in useful energy (based on measured PAR, spectrum analysis, etc.)

Even a longer tank, such as a 6 foot aquarium can have 3 or 4 T2s linked together to make a superior upgrade from outdated T8 or T12 lights many freshwater fish only tanks still employ, with an increase in useful light energy and a decrease in electrical operating costs due to vastly higher efficiency.
Source: T2 Aquarium Fixtures

Watts Per Gallon: As a generalization, 1 to 1.25 watts per gallon for a planted aquarium
For Marine Reef, 1.50 to 1.75 watts of the the 6400K lights (mixed with other light types such as T5 or LED Reef Blue for the UV-A Blue light necessary for many reef inhabitants)

SHO CFL Lights
SHO Lights have been used for a few years in hospitals and Commercial Nurseries/Hydroponics operations with exceptional results for plant growth, but these SHOs are a bit newer to the Aquarium hobby.

Dollar per dollar, there’s likely no better plant light, whether aquarium or terrestrial, especially when used in polished reflector to concentrate light energy.
See: SHO Aquarium, Hydroponics CFL, lighting

Watts Per Gallon: As a generalization, 2 to 2.5 watts of Daylight SHO Lights are required for planted freshwater aquariums
For Marine Reef, 2.25 to 2.75 watts of these SHO lights (possibly mixed with other light types for the UV-A blue)

T5 Lights
Although not as high in lumens per watt output than its newer cousin, the T5 has many sizes and wattages to fit more high lighting needs aquariums than the T2, and is a popular aquarium light for many good reasons (especially for many reef tanks).
However, many aquarium lighting needs would be served as well or better with lower initial cost and operating costs with a T2 Light; sadly many aquarists (& even aquarium/fish forums) are not even familiar with the T2 and continue to push T5 lights when in many instances the T2 would be the better choice

Watts Per Gallon: As a generalization, 2 to 3 watts of Daylight T5 Lights are required for high light planted freshwater aquariums
For Marine Reef, 2.5 to 4 watts of T5 lights (mixed with actinic UV-A blue)

T8 & T12 Lights

These are the old stand-by of the aquarium industry and are still good for fish only, FOWLR marine aquariums, and low light planted aquariums.
For Reef or high light planted aquariums, these are generally a poor choice, not because they do not work, but because it takes so many of these lamps to produce the results of more modern aquarium lighting options.

Watts Per Gallon: As a generalization, 3-4 watts of Daylight T8-T12 Lights are required for planted freshwater aquariums
For Marine Reef, 4-5 watts of T8 lights (mixed with actinic UV-A blue)


As a guide I will make a few suggestions in the following section using a 20, 60, or 100 gallon aquarium, which can then be extrapolated either up or down for larger or smaller aquariums.
Please consider the more in depth article, your personal aquarium parameters, inhabitants, budget (which is always important), when deciding what lighting systems or combinations there of to use.
Referenced From: Aquarium Lighting Set Up Suggestions

20 Gallon Aquarium Lighting Suggestions

60 Gallon Aquarium Lighting Suggestions

100 Gallon Aquarium Lighting Suggestions

Light (lamp) Placement:

Pendant vs. MirrorThe advantage to a pendant reflector over a mirror (depending on reflection quality) is that it will radiant downward in a slightly more magnified fashion than a mirror, however the mirror has one advantage over the pendant and that is more wide spread light distribution.
So this choice comes down more to tank arrangement of plants or corals.

Light Penetration/Delivery
What’s often a bigger issue, especially with deep reef tanks (over 24 inches) is to allow as much of the blue light {best penetration/delivery) as possible through into your aquarium, as often a glass top will block these light rays (over 60%), so using polycarbonate or no lid at all may do more for effectiveness than whether you use a mirror or pendent (see further in this article for more on this subject).

As well for tanks over 24 inches the use of some higher Kelvin “Daylight” in your light “mix” may be necessary for coral tanks or in some cases high light requiring plant tanks. The use of 14,000K MH in a mix with High PAR 6400K SHO lights may provide the “mix” necessary for deeper tanks.
Even in tanks under 24 inches, the use of actinic blue lights may help provide the correct PAR to specimens lower in your tanks water column; a HO LED light strip may help provide this.

Here are two sellers of these aquarium light products:
SHO Lights &
AAP AquaRay HO LED Lights

It is worthy of note if a LED aquarium light is used, that unlike all other lights generally used in aquarium lighting, these are actually light emitting electronic devices, so protecting these from excessive moisture is important just like you would not subject your computer tablet to undue moisture.
More importantly yet, all but one LED fixture sold for aquarium lighting has a water resistance rating of IP66 or less. The highest rating is IP67 and only the AAP AquaRay line has this rating.
This says a lot, as you might save $30 up front with a Current or Finnex LED [with IP65], but when you consider the risk of damage and poor warranty [as little as 180 days compared to 5 years for the AAP AquaRay], this price savings for what is already a lower output of both quality and quantity of photon light fixtures per input energy, there is really no logical reason to purchase and no amount of optimum light placement will fully protect these poor water resistence light fixtures so commonly sold at discounters.

Specimen Placement

Specimen placement is just as important as light penetration, since a SPS coral or Maxima Clam placed 12 inches under the the water will receive more light energy than these same specimens at 24 inches (this goes for freshwater plants too).
I recommend corals be placed as high up in the water column as possible, this especially important with SPS corals (short polyp stony corals) where placement on the rocks directly under your lights is even more essential.

This is not as essential with LPS corals (long polyp stony corals) since they are more commonly found in sandy lagoon bottoms.
If this light is for Freshwater plants I would move the high light requiring plants directly under the lights (or even elevate them with terracing, which can look quite attractive if done well and serve a dual purpose of aesthetics and better light energy absorption).
Further Reference: Freshwater Aquarium Plant Care, Information

Another aspect of specimen placement is the type of light used.
All fluorescent lights have what is called “Re-Strike” as light is sent in every direction, then striking objects and re-striking the lamp itself, often multiple times, hence “Re-Strike”.

Unless you are using a reflector, which is recommended whenever possible such as with SHO lamps, the area of best placement is not too well defined other than right under the tube or CFL.

The problem with fluorescent lights (in particular without a good conical reflector), is depth penetration; so placement of delicate specimens need to be as close to the surface as possible, in particular with lower powered fluorescent lamps. This is not as much as issue with some HO T5 and SHO lamps.

However, as per Metal Halide or LED lights; these lights have a clearly defined cone under the lights where the Lux/PAR gets lower the further from the center of this cone of light you place your important light sensitive specimens.
So with this in mind, it is important to place high light requiring corals, plants, clams, etc as close to the center of this cone as possible, while placing less sensitive plants, soft corals, etc. further out from this cone of light.

For the full article from which much of this information in this article was used with permission from, including Lighting Types and vastly more expanded & updated lighting information:

Copyright 2019, By Steve Allen


*Aquarium or Pond UV Sterilizer Use; Level One
This is an excellent article for those who value their fish. While many persons have use so-called UV Sterilizers, what in reality were used were UV Clarifiers. This article set this difference straight and explains why spending more money for a true level one UV Sterilizer is worth the investment.

*Saltwater Aquarium Care Information

For the best in premium hot cathode 95% UVC emission UV Bulbs, I suggest these as per my many friends in the aquarium industry/hobby:
* UV Bulbs; For Tetra, Turbo Twist, more

* AAP Wonder Shells
The ONLY authorized online seller of the unique AAP Wonder Shell, including the “patent pending” Medicated version. BEWARE of a broken Google algorithm that directs searches to clearance stock that is not fresh and not authorized!!!