mr_z
New member
http://www.chucksaddiction.com/lights.html[/url
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.
what the reefs are subject to~ 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.
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.
I agree, you just don't get the "pop" if you only run daylight bulbs...