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This area of reef keeping is of course extremely important, every coral species that we normally see within an aquarium depends upon its source of light to maintain its symbiotic algae that live within its tissues and can provide a good bit, but not all of its nutrients, which is why coral reefs flourish in water zones that are devoid of almost all dissolved nutrients. To recreate the light conditions that a reef is subjected to and adapted to is the goal of all reef hobbyists. As with everything in this hobby, theres more than one way to do this. Most hobbyist's highest equipment cost is the lighting systems. There are numerous makes and models specifically made for our reef tanks all of which can consist of different types of lighting and combinations of such. This page will not delve into that complicated subject, although links will be provided that do. 

    Not something often asked and yet, if we do not know the physics of light as well as how light can be used by photosynthetic life forms, it would make understanding what a specific habitat  is subjected to all but impossible, which is after all, what we should be trying to emulate.

 What is Light    Part two  -  " The purpose of this series of articles is to provide beginning and intermediate reef aquarist with a comprehensive understanding of lighting concepts and terminology, and the ability to understand and comprehend lighting related discussions and data.  "

 The sun is a mass of incandescent gas  -  "  It is important to understand what the sun is and does, because upcoming articles will be comparing the differences between using sunlight to using common aquarium lighting in the home aquaria. "

 Color Temperature ( Kelvin )  -  " Understanding color temperature starts with understanding black body radiation and the Kelvin temperature scale.  "

  Some commonly used terminology used in regard to "lights" , But in short,  A lamp (bulb) produces a certain amount of light, measured in lumens. This light falls on surfaces with a density measured in foot candles or lux.  While a bulb's light intensity is important, color (kelvin) and operating temperature should be considered also.

  Wattage -  Simply a measurement of how much power an appliance uses .  Watts = Amps x Volts
   For light bulbs, wattage simply means the more power (wattage) that is used, the more "light" it emits. But not all light bulbs are created equal. Why do we not get the same light intensity from a 100watt incandescent bulb as a 100watt metal halide bulb? Simply because light is produced from heat. The hotter a bulb can "burn", the more light it will emit. Metal halides can simply produce more heat than an incandescent bulb using the same amount of power. If not, then I would have two 150watt  incandescent bulbs that cost four bucks over my tank and be done with it.  For a more in depth explanation about wattage, voltage and amps, please see this link.

  Lumens -  A unit of measurement of light.  To understand what a Lumen is, you have to understand what a Foot Candle measurement is. Which is the amount of light that will hit an object held one foot away from a single candle. A lumen measures light much the same way. Remember, a foot-candle is how bright the light is one foot away from the source. A lumen is a way of measuring how much light gets to what you want to light.  A LUMEN is equal to one foot-candle falling on one square foot of area. For more information on Lumens, please see this link.

  Lux  -  Just another unit of measurement.  One Lux is equal to one Lumen per square meter.

  Par ( Photosynthetically Active Radiation ) -  This is the unit of measurement that we should be concerned with as it measures units as micro-Einsteins per meter squared. Thankfully the cost of the measuring devices have come down greatly and can be had for cost of a good powerhead pump. Such a device will take all the guess work out of knowing if your light system is providing what your reef needs. Which when measured in PAR, should be between 300 to 800 par throughout the aquarium. Anything between that range is more than enough to maintain any type of coral. When shopping for specific brands of bulbs and ballasts, this linked website will provide you the information needed.

  Kelvin  -  Simply put, it is the color scale of light. The higher the kelvin rating of a bulb, the more bluish it will appear. For reef applications, I would go with a bulb in the 10,000 to 14,000 kelvin range. See the above link about Kelvin for more information.

  Intensity  -  A term often used to describe how much light (photons) is actually hitting an object. Another way to look at intensity is to describe it as photon density. The more dense the light is, the more photon particles are hitting an object at any given time, which makes it "brighter".

  To simplify the entire matter of what light system to put over a reef aquarium. Placing a 14,000 Kelvin, 175 watt Metal Halide bulb for every two foot length of tank will ensure that you can keep any coral species that you wish. Of course, depth placement of coral within such a setup will be determined by the corals species.



    Since we remove animals from their natural habitat to be kept as pets, we then have the responsibility to do our best to recreate those habitats in which they came from. To do so, understanding those habitats and knowing what those habitats provide is crucial  in our recreation attempts. I often see the mistaken belief that all reefs are created equal. In that, they all receive the same light intensitys and water flows. I think a great many hobbyists would be surprised to see how variable reef /ocean conditions are, even within just a few miles of each other.

 Underwater Lighting Conditions  -  " The purpose of this article is to discuss the factors that affect the quantity (irradiance or light intensity) and quality (color or spectra) of light reaching organisms living in the ocean "

 Underwater Light fields and its comparison to metal halide lighting  -  " How does the light over our aquariums compare to that on a natural reef? This article presents some data on the underwater light field on a reef and compares it to the artificial light field over our reef aquaria "

   
     If you have read the above linked articles, you should have a much better understanding     of not only what light actually is, but also how much "light" is provided for in the various           coral habitats. The following linked articles will explain how we can provide for the needs of our light loving pets.  For specific coral species needs, as well as how corals use the light we provide for them, please see my coral page for many good article links on that subject.

 AQUARIUM PHOTO PERIODS :  If you are keeping a tropical reef aquarium, it would make sense that your corals and other inhabitants came from a tropical location, which means being near the equator. At the equator, each day light period is roughly 12 hours, each and every day of the year. While it may not seem important to reduce or lengthen the lighting periods, doing such things can pose a risk to your pets. A reduction in the length of the day may not provide enough photosynthesis for the corals symbiotic zooxanthellae, or allow any decorative / functional algae to perform its job of nutrient reduction. A extension of the photo period could also be harmful to the corals over the long term as it has been shown that extended lighting periods can actually be detrimental to coral growth and long term health.
   Keeping with an equatorial lighting theme, in my opinion, a combination of lights that will allow you to simulate a sun rise, a high noon intensive period and a sun set would allow for a much more natural environment. To do so, I would have a few compact fluorescent or anything else such as T5 or Power compacts that can be turned on and off independent of the metal halides.  As an example of what I would consider a "perfect" lighting system, I would want at least four T5 bulbs or two power compacts and one 250 watt 14,000 Kelvin Metal Halide (one MH per two foot tank length).  
  Lets say I have four T5 bulbs and a metal halide system, in order to simulate a 12 hour day, I would do the following : (times given are just an example and can be adjusted to your schedule or needs)

  7 am - Two of the four T5 bulbs turn on.  (or one power compact turns on)
  9 am - The remaining T5 bulbs turn on.  ( or the second power compact turns on)
 10am - The metal halides turn on.
  3pm - The metal halides turn off.
  5pm - Two of the four T5 bulbs turn off  ( or one of the power compact turns off)
  7pm - The remaining T5 bulbs turn off  ( or the remaining power compact turns off)
   The use of a few LED lights for night time viewing is optional here, I prefer not to use them as my tank inhabitants, including the fish, do not exhibit what should be normal dark period behavior with any ambient light being on.
    Also keep in mind, that being "tropical" means that every day is not a clear sunny day, there are a great many dark cloudy days and there is nothing wrong with leaving the metal halides or other intensive lighting off for an entire day once a week.  Also, if you use any bulbs that are 10,000 kelvin or greater, there is no reason what so ever to also use actinic supplementation. Such use of those bulbs goes back in history when the hobby only had 6,500 kelvin (or lower) bulbs available and to better simulate the kelvin as received by corals at depth, such low kelvin bulbs had to be supplemented with actinics. I am to this day still amazed that with 20,000 kelvin bulbs available, or any kelvin for that matter, we have not broken the habit of using actinics on already too "blue" of tanks. So stop it will ya!, unless of course you are using 6500 kelvin bulbs.


Analyzing Reflectors : Mogul Reflectors  Part Two  Part Three  Part Four - " Clearly from the hobbyist’s perspective finding the most cost effective way to light the tank is often an important concern.  Balancing the needs of corals, costs and aesthetics all come into play when deciding on a lighting system. "  Part Five : Metal Halide Lamps and Ballasts

 Lighting the Reef Aquarium, A primer for beginners  -  "The most important consideration for reef tank lighting lies in choosing a lighting system based on the requirements of the animals that we wish to keep."

 Thoughts on Reef Aquarium Lighting  -  "The goal in lighting your photosynthetic creatures is not to have optimal hardware… but optimal health of the animals themselves, by whatever means. "

 Lighting in Reef Tanks, some actual data  -  "Various authors have tried tackling this subject, covering light from a wide variety of angles, from different bulbs, to different ballasts, to different reflectors. Yet no one has characterized light fields in actual aquariums which is what I aimed to change. "

 Classification and Terminology for reef Aquarium Lighting  -  " Experienced aquarists agree that while corals naturally adapt to varying lighting situations, certain guidelines and levels are required for differing corals. A nominative scale is currently used in the aquarium hobby as low light, medium light, and high light."













  My Reef Aquariums Lighting System:

  I made my own canopy out of 3/4 inch plywood and painted with an enamel paint.  In keeping with as natural a photo period as possible, I employ two different types of lighting which are turned on and off at various times within a twelve hour period to simulate a low light sun rise, a high noon intensive period, and a low light sun set.  To achieve this type of photo period, I use household compact fluorescent bulbs in a variety of wattages, all are a 6,500 kelvin. Instead of trying to place my coral species to the lights, I have placed the lights to where I want my various corals species. On the right side of the tank, there is a single 100w CF bulb and a 35 CF bulb. On the left side, there is a 55w , a 35w and a 26w CF bulb. At the back of the canopy and off center to the right there are two more 26w CF bulbs.  In the center of the canopy I have placed a single 250w, 14,000 kelvin Metal Halide bulb which is used from 11am untill 3pm to achieve the intensive high noon effect.  With this type of lighting arrangement and intensity, I am not limited in the coral species that I can keep. If I need more or less intensity, with the wooden sides and back of the canopy, I can rearrange, add or reduce the CF bulbs very easily as you only need a socket and a power cord to power the CF bulbs.

   
6,500 kelvin Household Compact Fluorescent Bulbs and a single 250w Metal Halide
 
Exhaust fan and the Reflective tape used within the canopy






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This mirror is being hosted with the permissions of the original content creator for preservation and educational purposes.