  
AQUARIUM LIGHTING, Kelvin, Nanometers and more.Including: • Basics • Kelvin Rating • Nanometer Range (Spectrum) • PAR (Photosynthetically Active Radiation) • Lux • Lumens • Watt • CRI • Bulb Type (T-2, T- 5, SHO, VHO, MH, LED, Moonlites, Induction, etc.) • Summary including applications for Freshwater, saltwater, freshwater plant, Nano reef, and advanced reef |
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AQUARIUM LIGHTING By Carl Strohmeyer Updated 9/05/08  When choosing lighting for your aquarium (especially Reef or Planted Freshwater), there is much more to consider than watts per gallon. The 2-3 watts per gallon for a reef or freshwater plant aquarium, less for fish, more for hard coral; is a VERY basic start but that is very general and quite out dated due to the variety of lumens per watt lights with very different wavelength, PAR output. As you will read more later in this article a watt is simply a measurement of energy NOT light output or even quality. There are other factors effecting lighting for your aquarium than just watt output. For example: You cannot compare the output of a 150 watt Metal Halide to a 150 watt outdoor floodlight. Nor an 85 watt standard incandescent to a 85 Watt 6400 K SHO Bulb. What I am trying to say is sometimes it comes down to comparing apples to oranges. Other considerations besides energy used (watts) are PAR (and other wavelength needs of the aquatic environment), Lumens per watt and the amount of space a bulb will occupy which allows for more or less lights depend on the size of the bulb. For example a SHO that uses 105 watts yet is only 10” and placed into a reflector will be very efficient as per wattage and space utilized for this. Another example is a T-2 bulb that only takes up a small space (7 mm diameter) can be a very productive bulb as per lumens per watt (73 lumens per watt!), PAR and space used. For example I would recommend a pair of 19 inch/13 watt/ 6400K T-2 over a pair of 18 watt standard (T8 or T12) for a 20 gallon planted tank; the reasons are higher lumens per watt (73 vs. 40-50) and correct temperature/PAR (6400 K vs. 2100 -4500). Another note with freshwater plant light requirements is that the 3-4 watts per gallon general rule applies to medium to high light plant requirements, not low light such as Java Moss, or in the case of Reef Aquariums stony corals such as Acropora. This is just an brief explanation, please read further for more in depth discussion (and I do not assume this article is the end all of aquarium lighting discussion, I will add a lot more as time goes on and there are of coarse some even more in depth articles available). Here are other important factors; [1] KELVIN RATING (such as 10,000K daylight bulb): Although I do not believe all the manufacturers are totally honest about true Kelvin output, I believe it should be considered. Kelvin is used to define the heat or energy output of a bulb and if this is applied to two 36 watt PC bulbs, one 6500K the other 10,000K (often daylight or power glow), the 10,000K bulb has a higher energy output. What the true definition of Kelvin is that is a unit of measure of temperature on the thermodynamic (absolute) temperature scale. Here is a brief description of Kelvin: Kelvin is defined by two points: absolute zero, and the triple point of pure water. Absolute zero is defined as being precisely 0 K and –273.15 °C. Absolute zero is where all kinetic energy (motion) in the particles comprising matter ceases, and they are at complete rest. At absolute zero there is NO heat energy. The triple point of water is defined as being precisely 273.16 K and 0.01 °C. Here are a few Kelvin numbers: *Absolute zero = 0K (-273.15C) *Waters freezing point = 273.15 K (0 C) *Waters boiling point = 373.1339K (100C) A few notes about Kelvin: * Plant chlorophyll absorbs light at wavelengths of 300 to 700 nm (a Kelvin rating of about 6400 strikes a good balance here) * The lower the “K”, the more yellow the light appears, such as a 4500 K bulb. * The higher the “K”, the bluer the light appears, such as a 20, 000 K bulb. * The human eye sees mostly sees light around 5500K. The Kelvin rating is another area of comparing apples to apples in lights, not just watts. [2] THE NANOMETER RANGE (SPECTRUM) A nanometer scale is used to measure the wave length of light energy from cosmic rays to radio waves. An actinic bulb will have a Nanometer spike at about 420N, a UVC bulb about 265N, and a daylight bulb about 700N. The difference in the wavelength determines how the wave affects its surroundings. It is this wavelength difference that allows short-wave x-ray to pass through walls, while longer-wave visible light cannot pass though the same material; short-wave ultraviolet and x-ray can destroy DNA in living microorganisms and breakdown organic material while visible light will not. All light energy is measured on a "nanometer" (nm) scale. Nanometer means one-billionth of a meter. This applies to aquariums when we consider the light spectrum and how it applies to our aquariums individual needs: Red light is the first to be filtered out and can only penetrate a short distance. As light waves penetrate deeper into the water, orange and yellow are lost next. Of all the colors of the spectrum blue light penetrates the deepest. Corals need intense equatorial UVA (actinic) and even some UVB as recent articles (and my own experience) suggest. Most plants need both actinic and infrared light. The Nanometer scale and Kelvin temperatures come together when applied to aquarium lighting this way; Natural sunlight on a clear day registers at 5500 Kelvin degrees. Kelvin temperatures less than 5500 become more red and yellow and the higher the Kelvin temperature the more blue the light is. Most photosynthetic invertebrates should be kept with lamps of a 20000K rating. Actinic emits a fluorescent blue light and is usually used as supplemental lighting. Not only is actinic lighting beneficial to photosynthetic invertebrates, it is also aesthetically pleasing to the eye when used to supplement "daylight" lighting. Freshwater aquarium plants benefit from lighting with a Kelvin temperature in the range of 5500 - 6500 degrees. Freshwater plants prefer light with more red and yellow in the spectrum. What the exact Kelvin output of an aquarium bulb is takes a little faith in the manufacturer (at least in my opinion), as it is difficult to test each manufacturers claims of Kelvin and the application of Kelvin to aquarium bulbs takes a little bit of scientific stretching (based on the definition of Kelvin). [3] LUX: A measure of the intensity of light (referred to the photometry of light), one lux is equal to one lumen per square meter. This is important for aquarium plants. Once again this is another area of comparing apples to apples in lights, not just watts. This is also VERY important to most corals in marine reef aquariums. When the Lux (intensity) is not enough the zooxanthellae (algae that are inside of corals tissues) do not create plentiful oxygen. The minimum light intensity should be no less than 3,000-lux when it reaches the deepest part of the aquarium. You can over light your coral to a light saturation point (quite hard in my experience, but this should be noted), maximum Lux should be no more than 100,000 to 120,000. A lux meter is an excellent investment for a serious aquarium plant or Reef hobbyist. Here are two sites I found with these products: "Ultralife Lux Meter"; "Light Intensity (LUX) Meter"  [4] PAR: Probably one of the most important considerations along with lumens per watt and watts per gallon when choosing a light for your aquarium. PAR is the abbreviation for Photosynthetically Active Radiation which is the spectral range of solar light from 400 to 700 nanometers that is needed by plants for photosynthesis (actinic UVA to infrared). Photons at shorter wavelengths (Ultraviolet –C or UVC) tend to be so energetic that they can be damaging to cells and tissues; fortunately they are mostly filtered out by the ozone layer in the stratosphere. Green light occupies the middle spectrum (what is mostly visible to us) and is partly why chlorophyll is green due to the reflective properties. Bulbs that emit mostly actinic light will have a lower PAR such as the Helio Super Blue. Chlorophyll, the most abundant plant pigment, is most efficient in capturing infrared and blue light (ultraviolet).  Botanists argue that blue light is the most important for leaf growth and that red light encourages flowering and general health, meaning you would need more ultraviolet for more plant growth. Generally lighting with a Kelvin output of 6400 K occupies region of peak PAR and are the most desirable for plant growth (which is Kelvin rating of the sun's light in the tropics at noon).In fact despite anecdotal claims passed around within the aquarium hobby; in better funded tests outside the aquarium industry show that many stony corals, clams, and other sessile species that depend on photosynthesis of zooanthellic algae not only thrive but also propagate with light that achieves the optimum PAR, which is generally found around 6400K, not the higher Kelvin ratings so often put forth (Higher Kelvin outputs are required for tanks deeper than 24-30 inches to achieve maximum PAR, although high intensity 6400 SHO lamps can generally penetrate deep tanks well). To be even more blunt (and possibly upset some of the “reef keeping police”), many more recent studies show that excessive UVA and UVB radiation can actually bleach coral and in an aquarium environment lights with more UVA or UVB are not generally necessary as although a lamp with more “blue” such as a 20,000 K MH may penetrate more deeply (due to the fact that infrared light gets absorbed the deeper the light must penetrate), in all but the very deepest aquariums this 20,000 K MH is simply a waste! With this in mind it should be noted that lamps with both red and blue spectrums will do well for plant growth in BOTH freshwater and saltwater, despite some claims that blue is only for saltwater aquariums (there is not a difference in chlorophyll production in freshwater from saltwater that I know of). Some organisms, such as Cyanobacteria, purple bacteria and Heliobacteria, can utilize light in regions such as the low infrared. These bacteria make use of the unusable light discarded by the plant kingdom, in this case, light outside the PAR range required by plants, which is why Cyanobacteria thrive in lighting conditions that include the more yellow 4000 K and below and why actinic as well as balanced light in the 6400 range combined with passing water through an ultra violet sterilizer (to kill free floating Cyanobacteria) is important for control. One final note; please do not confuse the term PAR (Photosynthetically Active Radiation) used in plant growth as discussed here with another use of the same term in lighting which is Parabolic Aluminized Reflector. This type of light is used for stage lighting and should not be purchased for marine, freshwater, or Greenhouse use under the mistaken belief that these lights are “great” for plant/coral growth. For further reading (references) about PAR: *Light and Plants *A rational approach to light measurements in plant ecology *Photosynthetically Active Radiation *http://www.aquariumpros.com/articles%20PDF/lamptypes.pdf [5] LUMENS: The international unit of luminous flux or quantity of light used as a measure of the total amount of visible light emitted. The higher the lumens, the “brighter” or more “intense” the light looks to the human eye. You can figure lumens per watt by dividing the lumens your lamp lists by the wattage the fixture lists. Knowing your lumens per watt is often as or more important than watts per gallon. For example a T12 light that is rated at 20 watts with a total lumen output of 800 lumens has a lumen per watt output of 40. While a 13 watt T2 bulb rated at 950 lumens has a lumen output of 73 lumens per watt. This is a clear example that the watts per gallon rule is severely flawed as the 13 watt T2 (or two of these) is clearly the better choice for a 15 gallon planted aquarium (or reef) and this does not even take into consideration the PAR rating which is also important for plants/corals or lumens per length of bulb (space). This lumen comparison also applies to SHO, VHO, and Metal Halide all of which far out produce most T12 lamps in lumens per watt. [6] WATT: Watts equal one joule of energy per second. For us, it’s a measurement of how much energy our light fixture is using NOT of light output! This why the 2-3 watts per gallon for FW plants (3-5) for reef can be deceiving, and this rule is only a starting point similar to the 1 inch of fish per gallon “rule”. This archaic rule was more accurate when all that was used were T12 lamps which is what this rules is based on. Keeping this in mind the average T12 has a lumens per watt rating of 40, which means you would need half as many watts of a bulb that produces 80 lumens per watt (assuming PAR, Kelvin and other aspects are equal) The term “watts per gallon” is getting more archaic as newer T-2, T-5, compact Fluorescents, and especially the SHO and some of the new reef compatible LED lights have more watts spread over less distance. Keeping this in mind; ‘watts’, when applied to a standard fluorescent tube are spread over longer bulbs as the wattage increases. For instance a standard 30 watt T 8 bulb is 36” while a standard 20 watt T-8 bulb is 24”. For high light requirements such as plants or reefs, at least 1 inch per watt is required when comparing tube style fluorescents bulbs. Many high output light such as the Metal Halide or the more economical SHO PC bulbs use a lot of watts in a small amount of space. The 110 watt SHO bulb uses 110 watts in 10” or even less if mounted in a pendant. Another aspect of watts is the output of lumens per watts actually used. The output of a 400 watt incandescent bulb is about 25 watts of light, a 400 watt metal halide bulb emits about 140 watts of light. If PAR is considered to correspond more or less to the visible region, then a 400 watt metal halide lamp provides about 140 watts of PAR. A 400 watt HPS lamps has less PAR, typically 120 to 128 watts, but because the light is yellow it is rated at higher lumens (for the human eye). [7] CRI: To help indicate how colors will appear under different light sources, a system was devised some years ago that mathematically compares how a light source shifts the location of eight specified pastel colors on a version of the C.I.E. color space as compared to the same colors lighted by a reference source of the same Color Temperature. If there is no change in appearance, the source in question is given a CRI of 100 by definition. From 2000K to 5000K, the reference source is the Black Body Radiator and above 5000K, it is an agreed upon form of daylight. A CRI of 100 has a heavy red spectrum. The color temperature is 2700 K for incandescent light and 3000 K for halogen light. An incandescent lamp, virtually by definition, has a Color Rendering Index (CRI) close to 100. This does not mean that an incandescent lamp is a perfect color rendering light source. It is not. It is very weak in blue, as anyone who has tried to sort out navy blues, royal blues and black under low levels of incandescent lighting. On the other hand, outdoor north sky daylight at 7500K is weak in red, so it isn't a "perfect" color rendering source either. Yet, it also has a CRI of 100 by definition. CRI is useful in specifying color if it is used within its limitations. Originally, CRI was developed to compare continuous spectrum sources whose CRI's were above 90 because below 90 it is possible to have two sources with the same CRI, but which render color very differently. At the same time, the colors lighted by sources whose CRI's differ by 5 points or more may look the same. Colors viewed under sources with line spectra such as mercury, GE Multi-Vapor® metal halide or Lucalox® high pressure sodium lamps, may actually look better than their CRI would indicate. However, some exotic fluorescent lamp colors may have very high CRI's, while substantially distorting some particular object color. Technically, CRI's can only be compared for sources that have the same Color Temperatures. However, as a general rule "The Higher The Better"; light sources with high (80-100) CRI's tend to make people and things look better than light sources with lower CRI's. Why use CRI if it has so many drawbacks? It's the only internationally agreed upon color rendering system provides some guidance. It will be used until the scientific community can develop a better system to describe what we really see. It is an indicator of the relative color rendering ability of a source and should only be used as such (Source: Color Rendering) [8] AQUARIUM BULB TYPE: Common aquarium bulbs include the: *T-12; a standard pin, 1-1/2” wide bulb. This bulb will generally use more watts and have a lower lumens per watt ratio (usually around 40) and is common in shop lights and even many aquarium bulbs. These are generally the least expensive lamps to purchase and even though they may be “old school”, these still may make up for there low technology with the fact you can purchase several for a low price to make up for poor efficiency. The main caution I would add to these of these bulbs for aquariums is many forums often suggest the use of shop lights as an inexpensive alternative to many aquarium lights, however a 4100 K cool white shop light is not going to come close to a 6400 K daylight lamp that is of peak PAR efficiency (even if you match lumens). *T-8; a standard pin, 1” wide bulb. As compared to the T-12, a 48” T-12 will use 32 watts, while a 48” T-8 will often use 32 watts (although not always). This is the more common bulb/lamp size in many basic aquarium lights. *T-5; Generally around 13 mm in diameter. This is a mini pin bulb which generally uses even less watts per lumen than many than T-8 bulbs. A common lumens per watt output for T-5 lamps is around 60  *T-2; These bulbs are the latest technology yet. They measure only 7 mm and allow for several bulbs in a small space. A 13 watt 20 inch T-2 Bulb (6400 K) produces 950 lumens which is 73 lumens per watt in a very small space!Quite bluntly, these T2 lamps and fixtures are about the best bulbs in a small space I have seen! These are very useful for small to medium planted aquariums  or Nano Reefs or even shelves for betta breeders. The linkable fixture feature is also a nice aspect of these T2 lights/fixtures (this allows for use in larger aquaria such as 60 gallons PLUS). I expect these new T-2 lamps to sweep the small to medium aquarium keeping hobby due to their extremely high efficiency and out put. In fact these lamps are even a good choice for many aquariums such as 60 gallons and larger since each fixture can be snapped together forming a larger fixture (similar to some T5 fixtures, which are also good fixtures, just not quite up to the more modern T2 in efficiency). For instance I have used two T2s snapped together for some 60 gallon FW aquarium and two sets of two (placed in parallel in the hood) for planted 60 gallon FW aquariums (these also work well in Marine Aquariums since these lamps have a high output in PAR required for symbiotic algae that live within corals).  *VHO this stands for “Very High Output”. These come in T-5 thru T-12 standard fluorescent tubes and in the newer power compact (usually 4 pin) lamps such as the New generation Via Aqua Helios VHO . The new Helios come in a variety of sizes with outputs up to 180 watts out of lamps under 40 inches in length, which rival many Metal Halide (although not in depth penetration). These new higher output VHO fixtures/lamps have higher Kelvin and wattage output than previous generation VHO lamps/fixtures of similar size. These can be used for both marine reef applications as well as freshwater planted aquariums (these new VHOs are not scheduled for full release to the public until early 2008). *PC (or CFL); this stands for “Power Compact” or “Compact Fluorescent Lamp (light)”. These bulbs come in straight pin arrangements, square pin arrangements, and the ever more popular self ballasted standard incandescent fixture “screw in” type. These bulbs are similar to T-5s and have about the same lumen per watt output (generally around 60 lumens per watt).The standard medium base version of these lamps will fit in a common incandescent light fixture, making these lights about the most economical lights you can purchase with this kind of output. These are an excellent choice for use in planted Freshwater or even Marine  Nano Reef tanks under 30 gallons (or even larger aquariums when multiples of these are used), especially when the hood already contains incandescent fixtures, as you need not purchase special fixtures for these. See the picture to the left as an example, please click to enlarge These self ballasted high PAR lamps are inexpensive and make it hard for even an aquarist on a budget (even a freshwater fish only tank) to not provide the best possible lighting for optimum plant and even fish and Nano reef health!  A newer fixture that incorporates these CFL self ballasted bulbs is the Eco Light which optimizes the lumens produced with a reflector that I have tested to increase output more than 50% over a the same light without the fixture in a standard aquarium hood. *SHO Power Compact Lights:A new Power Compact that in my opinion is awesome for planted aquariums and even for reef aquariums (as an addition to LED or Metal Halide) is the self ballasted SHO PC bulbs. The 105 Watt SHO Daylight bulb puts out 6300 lumens and is comparable to a 525 watt Standard bulb (click on the picture for a link). This comes out to 60 lumens per watt; however this is a deceptive guide, as you can fit many more of these bulbs in a given space and also utilize more efficient reflectors.The SHO can be mounted into your hood using a standard incandescent fixture or better, hung as a pendant light using reflector similar to how Metal Halides are commonly installed. These SHO lamps are also an excellent compliment to VHO or other “strip” lamps for use in reef tanks (in part due to their high intensity in small space and PAR output which is important for the symbiotic coral/algae relationship). Research has shown that many stony corals, clams, and other sessile species that depend on photosynthesis of zooanthellic algae not only thrive but also propagate when maintained under Power Compact lighting alone.  *Metal Halide (MH); These are the reigning “Kings” of reef aquarium due to depth penetration, output, spectrum, and over all beauty and amount of coral life they help support. Even the newer T-5 lamps cannot achieve the depth penetration and overall output of these lights. Metal Halides generally have very good lumens per watt ratio (although I have seen a lot of variation and even incorrect ratings here); however it is safe to say that MH are generally found with lumens to watt ratios of 50 to as high as 90.Metal Halide work via a gas mixture of halides and other elements, the actual light production comes from the small bubble of gas that is held in place by metal wires and/or supports. The electricity running between them and the small gas bubble, heats them, similar to an incandescent filament. This is one of the reasons that Metal Halide bulbs give off more heat than other bulbs. The downside is the heat that MH lights produce, often resulting in the need for hood fans and even chillers. The sizes I most often have used are between 10,000 K 175 watts and the 20,000 K 250 watts for really deep tanks (over 30”). With the 12,500 K lamp what I currently recommend.  *LED: The new reef compatible LED is likely to take over the market as they become more readily available, the price comes down and watts per lumen come up. These lights do not have the heat problems and are very compact. LED lights may prove to be more suitable for aquatic life tank-lighting and reef tanks because they offer superior flexibility when compared with traditional fluorescent lighting. When LED lights operate, the photometric radiation remains within a narrow band on the electromagnetic spectrum. Specific photometric wavelengths are often beneficial to some aquatic plant life and reef tanks. Controlling specific wavelengths becomes possible through a basic network of colored LED lights connected to a digital LED controller. Since LEDs emit light only in very specific direction, the installer has the option to illuminate a precise area by simply rotating the polycarbonate tube casing. The water resistant casing also provides the LED circuitry with adequate protection against moisture and chemicals found within the fish tank or reef tank.So far the there are mixed reviews on the larger units such as the Solaris that replace the MH. The manufacturer of the Solaris claims “PAR light output levels equal to a 400W MH 20k. It uses 40% less energy than the 400W MH 20k fixtures it replaces. The life of the LEDs is approximately 50,000 hours, so it almost eliminates metal halide and fluorescent bulb replacements. All heat is radiated up and away from the tank; therefore, it does not heat the water like Metal Halides or Fluorescents. This eliminates the need for Chillers.” However data shows 20 lumens per watt, MH bulbs provide around 50 lumens per watt as the output. I still like the idea even at lower output simply based on the energy saving in air conditioning and the cost of a chiller often necessitated by Metal Halides. The Rio Mini sun are a small version for marine and freshwater tanks under 10 gallons:  LED Aquarium Lights; Rio (Taam) Mini Sun Lighting Fixture Here is an excellent review of the Polaris LED lights that also makes interesting points about PAR, and UVA/UVB in marine tanks with coral:Product Review: A New Horizon in Lighting: PFO's Solaris LED System Lunar (Moonlights) Often LED as noted above are used as lunar or moonlights. This is an area where anecdotal information seems to be the main information available. I will admit that I myself to not have any really good scientific tests to back up my own opinions here (although I have used moonlights and ran some tests). Essentially these are very popular for marine reef aquariums for both a low level “night light” and for simulating moonlight for corals and coral propagation. Where some of the misinformation comes into play is that many will state that fish need these of which there absolutely no scientific proof and also that corals need these for proper growth which also has no scientific evidence to back this up. Many marine aquarists assume from all the regurgitated literature and repeated websites is that corals must have high amounts of blue light often in the 20,000 K temperature for photosynthesis which again the scientific evidence does not support, the peak PAR is generally found in a Kelvin rating of about 6500 K (sometimes higher for deep tanks). Moon lights (lunar lights) do nothing to aid in this.  What lunar (moonlights) do perform for the marine reef aquarium is to simulate marine lunar cycles which are necessary for some fish and coral reproduction/propagation as Corals in the Great Barrier reef which spawn 3-7 days following the first 2 Full moons in late spring and early summer. Even here there is still a lot of controversy as to what cycle is best and how much light is best.From what I personally have observed combined with the opinions of other aquarium professionals is that even low level “white” lights such as 7 watt Christmas bulbs, nightlight bulbs, or even the Rio Mini Sun LED lights work just fine for this since this has shown to be a more of a low level light issue and timing issue that light quality or type issue. Adding or subtracting the amount/intensity seems to be the secret of simulating these cycles which can be accomplish easily either manually or with electronic timers (that can be set to more accurate monthly 29.5 day lunar cycles of lighting). Strategically placing these lights also shows evidence as to properly simulating this effect. Please click on the picture above/left for a larger animated version of the lunar cycle Another product that performs the action of duplicating the 29.5 day lunar cycle can be found here: Moon Computer If anyone reading this article has good scientific evidence to the contrary (or even to support) what I have just said about the use of lunar lights, please email me on my contact page with these references. Induction Lighting  Although not a new technology per say, it is new in regards to commercial availability as until recently, new developments have broken down the barriers of costs and technological setbacks, such as EMC interference, lumen depreciation, ability to dim and a useful range of available wattages.This type of lighting last up to 100,000 hours (often over 20 plus years under normal usage) and is another good candidate to replace Metal Halide Lights. Induction lights due not have the warm of times of MH or similar (20 second warm up vs. 10 minute warm up), use no mercury, have no filaments to burn out, and they produce half the heat (160 F vs. 300 F for a 200 watt Induction Fixture vs. a comparable in output 400 watt MH fixture). Induction Lights generally have a high CRI of 82 with a high lumen per watt output (surpassing most MH). Currently the main negative as per Aquarium use is that Induction lighting is only available in 5000 K Daylight vs. a better 5500-6700 K Daylight, although this is still a viable Kelvin temperature as per PAR especially when one considers the high output delivered with half the heat output. SUMMARY: Remember from all the information written above, that when deciding what lighting to get for your aquarium that the watts used is only one third or less of the equation in deciding what lights, what size and how many should be used. I will admit that I still will use the watts per gallon a starting point, but I do NOT finish with this either; this would be like starting a race in first gear and never shifting gears the entire race! Also please note that besides years of personal fresh and saltwater keeping experience, even more of this information I have written here comes from research comes from OUTSIDE the aquarium industry as way to much aquarium lighting information is just the same regurgitated information that just gets passed around in a small circle within the industry and hobby. Some examples include the lack of information about SHO or T2 bulbs that are often superior to more commonly recommended bulbs in the aquarium hobby, yet in much better funded lighting and horticultural industry literature these bulbs are much better known as well the amount of evidence that suggests a Kelvin temperature of 6500 K provides the best PAR for both FW plants and SW corals photosynthesis flys in the face of much of the common beliefs (especially in reef keeping) that a Kelvin rating of 20,000 is best. Important Parameters to consider when choosing a light for your aquarium (not a complete list): *Watts per gallon, *Lumens per watt, PAR (often easiest determined by Kelvin output), *Output in relation to bulb length (this is where T2 and Power Compacts excel). *Lux, I generally only consider this parameter in deeper Reef and occasionally deeper planted freshwater aquarium to determine if I am getting the proper light where it needs to be. 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 8-10 hours per day) this can be stretched to 12 months. Here is 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 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 brightest lights on for about 12 hours per day. Sometime with MH I will have them in a third cycle that is on for only abut 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 in benefit from this that can be scientifically proven other than aesthetics). • A BASIC FRESHWATER FISH (including some low light plants) tank does not need as much lighting and will often do well with one “Aqua Glo”, “Color Max” or similar (30 watt) light for a 60 gallon aquarium. A 6400 K Power Compact is also an excellent basic freshwater and inexpensive tank lamp. Please keep in mind that even though “Aqua Glo” and “Color Max” are a approximately 6500 K, they do not have the output (lumens per watt, lux) for any thing more than low light plants. It is worth noting for even a basic freshwater aquarium that better lighting will usually result in healthier fish and easier control of algae, especially Brown Diatom Algae (not actually an algae). Unfortunately for many basic freshwater aquarium hobbyists many commonly sold aquarium bulbs do not publish anything other than “aquarium light for that brings out fish color”. Besides the before mentioned Power Compact lights, the T2 lights are excellent lights that have good PAR for health, plant growth, less Brown Algae. Others worth considering that are also reasonable good lights are the Zoomed and Coralife Trichromatic as well as the ZooMed FloraSun and VitaLite. There are many others that have reasonable outputs in the 5500-8000 Kelvin range • A FRESHWATER PLANT aquarium needs more ultra-violet and infrared plus more lumens/watts of light. Photosynthesis takes place at the blue end and at the red end of the Nanometer curve (420 nm blue and 670 nm red). The "valley" is around 550 nm, this is where most visible light is present and is why plant leaves mostly reflect green light, while they absorb red and blue. This curve drops sharply below 400 nm and above 700 nm. This area of peak photosynthesis is referred to as “PAR” as discussed earlier. In aquariums where you cannot or do not want to have multiple bulbs, an approximately 6500 K bulb works best for plants. In smaller aquariums I now tend to use the economical Power Compacts with 6400 K Daylight (which tend to be full spectrum as far as green plant growth is concerned) and occasionally actinic combinations. An excellent bulb for plant tanks that will fit in a standard socket is the 6400K, 15 watt Fluorescent Daylight bulb for aquariums. This is a great plant and fish light; this bulb fits any standard incandescent fixture and is an inexpensive way to turn an incandescent hood into a power compact light fixture useful for plant growth in small aquariums! I especially recommend the newer SHO (Super High Output) Bulbs, high output (in a small space) T-2 and the T-5 bulbs. The T2 Fixtures now available can be mounted in a hood, placed on or above an aquarium, attached end to end to make a long fixture or overlapped, making these about the most versatile plant capable (or Nano Reef) fixture available today. An even newer bulb is the “new generation” VHO Helio which can be purchased in 50/50 and all daylight configurations and can be very useful for planted FW aquariums (these fixtures and lamps are scheduled for release in early 2008). Since plants use both green and red light for growth, the use of either full spectrum Trichromatic daylight or 50/50 (Blue/daylight) are useful for healthy green plant growth. I have seen it mentioned that blue actinic light will encourage algae growth, I find this only half true based on my observations and the current scientific data I have read. The blue light encourages all green growth, both plant and algae, so if the plants can out compete algae based on other parameters this should not be an issue. In my own switching between daylight only and 50/50 lamps I have seen no discernable difference (I will not that these are observations, not scientific tests). Incandescent bulbs have a high infrared output and do well with plants, but also put out a lot of undesirable heat and tend to more in the yellow spectrum as well (not to mention a 85 watt standard inc. bulb does not even come close to comparing to a 85 Watt 6400 K SHO Bulb in output even though they are of the same wattage). Cool white fluorescent bulbs should never be used in any aquarium as they only put out visible light (around 550 NM ) and not the spectrum needed by plants or even fish (although if enough are used one ca achieve enough PAR and lumens to keep plants alive). Keep in mind the light requirements of the plants you are keeping. As stated above, watts per gallon is not the only rule to follow for aquarium plant requirements. Know your plants and know your lights then loosely apply this rule. A final note as to freshwater plants, is that the more light (in correct PAR) you add, even in low light plants, the more the plants will require additional nutrients; in particular carbon. This can be provided by fish respiration, products such as Flourish Excel and CO2 generators, however in medium to high light plants you will likely need to supplement CO2 in some form or another. Please read this freshwater aquarium plants article for much more about this subject: “Planted Aquariums” • A BASIC SALTWATER or FOWLR tank also does not have as high of requirements, as but more than freshwater (especially if you do not want too much brown algae). A “Coralife 10,000 K” or “Hagen Power Glo” are reasonable basic saltwater lights. The VHO Helio are an excellent “step up” from basic. For smaller tanks the 6400 K CFL lights make a good choice and the SHO for larger aquariums. The newer T2 lamps are an excellent choice for smaller aquariums or even larger aquariums when the T2 fixtures are connected together. • A BASIC REEF OR NANO REEF: In a 10 gallon Nano Reef, two 15-18 watt 6400 K Power Compact bulbs will usually do well especially if used with a new high output T2 lamp. The new 6400K T-2 Lamps/fixtures are good compliment to a Nano Reef due to their compact size and high lumens per watt output and our now my choice for these tanks. As noted earlier, optimum PAR is what the coral needs and this is achieved best in lamps around 6400K, ESPECIALLY in smaller Nano Reefs! These fixtures can also be mounted in parallel and/or snapped together end to end for larger aquariums with higher output needs. Other considerations are a VHO Helio or even a 65 watt SHO bulb. The Helio bulbs come in actinic 50/50 combination for those still holding to the “old school” view that actinic is a must (albeit scientifically untrue!!!) • AN ADVANCED REEF with hard corals needs a combination of metal halide and standard fluorescent or CPF bulbs. On a 60 gallon reef aquarium I generally in the past used one 175 watt 8000- 20,000K metal halide (depending upon tank depth; in deeper tanks I use higher Kelvin MH) and one 10,000K daylight (40 watt) and one actinic (40 watt). However the SHO bulbs can work here as well as stated above: “Research has shown that many stony corals, clams, and other sessile species that depend on photosynthesis of zooanthellic algae not only thrive but also propagate when maintained under Power Compact lighting alone, provided they are of the PAR which usually falls around 6400K”. It should be noted that despite some of the common statements made in aquarium stores and here on the internet that 6400 K is where you will find the closest output to optimum PAR that is required by the symbiotic algae that live within the corals. The exception is that for tanks over 24-30 inches deep you will need a higher Kelvin output to achieve maximum PAR, usually 8000K to 14,000K to reach the bottom corals. These SHO lamps are a good replacement for most of the common standard fluorescents, CFL or even T5s for use with Metal Halide or possible by themselves (not enough data is in yet to say for sure if these SHO lamps by themselves are enough, although some research points this way). Marine Lighting Summary; I will point out that there is no one way to best light a marine aquarium, so my apologies for the multiple suggestions that may leave some scratching their heads wondering if there is one best lighting system for marine aquariums (especially reef). The answer is unfortunately NO! HOWEVER I will also stand up and state that many in the anecdotal side of aquarium reef keeping will state that the industry hobby standards are say a 10,000 K daylight and 420 NM actinic light for say a 20 gallon Nano Reef (this too is vague as watts per gallon, and even more importantly lumens per watt is another important factor). I will disagree with this standard as only anecdotal and simply passed around as fact (heck, I know I have used this “standard for many years myself before I started reading, researching, and testing more). What is often missed by those recommending say a 20,000 K light and or an actinic is that although the “blue” light radiation penetrates more deeply than say a 6500 K light, unless you have a 3 foot deep or deeper aquarium this is not all that necessary and in the case of some high intensity lights that produce high amounts of UVA (or even UVB) radiation (such as many MH) can actually cause coral bleaching. I will admit that the “blue” lights make for a more aesthetically pleasing marine aquarium, but in research I have read, my own use as well as by other professionals use of these lights is mostly just aesthetic. Now before I seem like I am knocking Metal Halide, I am not (outside of the high heat output), I just think aquarists often read into their good results with MH the wrong conclusion as to why they are good reef lights. MH are useful due to some of the highest lumens per watt of any light and their unique light dispersion that is often superior to other aquarium lights (there are other positives too). What I am trying to point out here is that there are other important factors, and in particular I want to stress lumens per watt and PAR (hopefully the reader has already read my sections about PAR and lumens per watt). All this said, some of the newer SHO, VHO and possibly LED show promise of replacing MH lamps. In fact these 6400 K SHO lights are already being used more by aquarium professionals for advanced reef aquariums, sometimes along with Metal Halide. This lamp would be my first choice and also require no special ballast (they fit standard Incandescent fixtures) I would also note as I did in the section for Nano reefs that the T-2 Lamps/fixtures are also a good lamp/fixture to use along with MH (especially when one considerers their versatility over standard fluorescents, and even CFL or T5s). The T2 fixture, the slightly older T5 and the 6400 K Standard Compact Fluorescent Lights all make good choices for many smaller marine aquariums (under 60 gallon). The bottom line is to start with an approximately 6500 K lamp (possibly 10,0000 K for deeper aquariums, but these are LESS efficient as to PAR, but penetrate deeper) and then add addition lights from there (including actinic if desired for appearance or just to make you feel better). • IMPORTANT- Another point about lighting in general is that higher wave lengths of light such as UVA do not penetrate glass well or even acrylic. I recommend direct lighting (best), quartz or polycarbonate where UVA is essential. Just make sure to clean your bulbs or polycarbonate tops regularly to prevent build up that will block light. Even though infrared will penetrate glass, it will not penetrate dirty glass with algae or hard water deposits on it, so keep your aquarium cover clean for any tank where lighting is important such as FW plants or Reef Aquariums. Here is a very basic breakdown of UV blocking potential: *Glass- about 60% of UV will be blocked *Acrylic- about 40% *Polycarbonate- about 8-10% (this is what I used when a lid was necessary) *Quartz- about .5-2% Here are more great sites with more information about light and lighting: "WHY IS WATER BLUE" "FACTS OF LIGHT- Color Temperature (Kelvin)" "THE KRIB- Aquarium Light intensities comparisons " "AQUA BOTANIC- A Comparison between Light Sources Used in Planted Aquaria"  A FEW POPLULAR AQUARIUM LIGHT BULB SPECIFICATIONS for older but still common aquarium bulbs (Hagen Flora Glo, Power Glo; Zoo Med Trichromatic, Flora Sun, Coralife 20,000 K, 10,000 K, and more):Please click to enlarge and view For more aquarium information and articles (pond too), please visit this site:   
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