Announcement

Collapse
No announcement yet.

Aquarium Lighting Overview

Collapse
This topic is closed.
X
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Aquarium Lighting Overview

    Aquarium Lighting Overview
    by Sean Danekind

    About 5 years ago I retired one of my 75 gallon cichlid tanks and converted it to a saltwater coral reef tank. I found that the saltwater coral reef hobby really appealed to my equipment junkie nature and dove headfirst into the world of high intensity reef aquarium lighting. I have no special training in the lighting industry or lighting in general. In fact, I barely remember my college physics classes that dealt with light and photons. The knowledge in this article is simply the sum of what I've accumulated after about 5 years of interest in the lighting aspect of the hobby.

    In 2003, I put together a presentation for the GCAS. I gave an updated presentation to CORA in 2006. This article is based on those presentations...

    So now I'm writing down everything I can think of that is useful for anyone new to reef tanks. I'm breaking this discussuion into a few easy to follow sections:
    What is Light?
    Aquarium Options
    Lighting Efficency
    Reef Tank Application
    References and Links
    9 to 5 sounds like a good night in Buenos Aires to me!!!

  • #2
    Part 1 - WHAT IS LIGHT?

    Before we get into how to light your aquarium, we need to answer a few basic questions...
    What is light and how do we measure it?

    If you whip out your old high school physics book, you'll find a detailed description of light. I'm not going to rehash all of that at the expense of boring everyone, so I'll just grossly oversimplify it: Light is something that can't decide if it's a particle or a wave, so it acts like a little of both sometimes. All we really care about is that we can describe the color and intensity of light.

    The color of light is commonly described in 3 different ways; Wavelength, Kelvin color temperature, and Color Rendition Index. The brightness of light is usually described using lumens and PAR, and is often affected by the distance between you and the source.

    Color - Wavelength

    Wavelength is actually a physical property of 1 photon (particle or wave, your choice) of light. you can't see anything in a room lit by 1 photon - if so, you'd be blinded by a candle. As we see it with our eyes, light is made up of millions of photons all at different wavelengths. What we call visible light is actually a very small portion of the electromagnetic spectrum. The wavelengths of light are Wavelength is expressed in nanometers (0.000000001 meters) between 400nm and 700nm. The entire electromagnetic spectrum that we can commonly relate to starts with huge low frequency radio wavelengths over 100 meters long and goes all the way down to X-rays and Gamma Rays that have wavelengths so small that scientists find it easier to refer the their energy level rather than a wavelength with a thousand decimals.

    Wave Type and Wavelength (m)
    Gamma-ray < 0.01 nanometers
    X-ray = 0.01 to 10 nanometers
    Ultra Violet = 10 nanometers to 400 nanometers
    actinic = 420nm
    Violet = 390 - 450nm
    Blue = 450 - 490nm
    Green = 490 - 570nm
    Yellow = 570 - 590nm
    Orange = 590 - 620nm
    Red = 620 - 700nm
    Infrared = 700 nanometers to 1 millimeters
    Microwave = 1 millimeter to 10 centimeters
    Radio = 10 centimeters to many kilometers



    Color - Kelvin Color Temperature

    Kelvin color temperature is another means of describing the color of light. In the mid 1800's, Scottish mathematician and physicist Lord Kelvin devised the concept of absolute zero - the temperature at which all movement stops, including electrons moving around atomic nuclei. Compare the Kelvin scale to Celsius and Fahrenheit:
    ........................*K........*C..........*F.. ..
    ------------------- ----- --------- ---------
    Absolute Zero....... 0 . -273.16 . -459.69
    Water Freezes... 273 ...... 0 ......... 32
    A Nice Day........ 297 ..... 24 ........ 75
    Water Boils....... 373 .... 100 ...... 212

    So, you're asking "How the heck does this relate to light?" The answer is - the heating element in your electric stove. It's basically black, but as you heat it, it changes color to red and orange. Take that concept and apply it to what scientists call and "Ideal Black Mass" (that just means it's a lump of black metal that behaves exactly as they expect it to). If you take this "Ideal Black Mass" and heat it to 6500 degrees Kelvin, it should light the room just like being outside on a clear and sunny day. The sun itself glows at around 5500 Kelvin, but the blue sky raises the color temp to near 6500 Kelvin. As you can guess from that example, red colors are lower in Kelvin color temperature and blue colors are higher.

    Here's another stunningly well crafted chart to help you out:

    ... *K . Color ................ Where you can see it
    ------- . ------------------ . ----------------------------
    2,000 . Yellow-Orange .. Sodium Streetlights
    3,000 . Yellow .............. Incandescent Lamps
    4,000 . Yellow-White ..... "Cool White" fluorescent lamps
    5,500 . Yellow-White ..... Sunlight
    6,500 . White-Yellow ..... Daylight
    10,000 . White-Blue ....... Daylight at about 10-20 meters under water
    > 10K . More Blue ........ Daylight at deeper than 20 meters under water

    Most aquarium lamps come in 6,500 Kevin color temp and up. Some fluorescent (NO, VHO, PC, T5) lamps are a mix of 6,500 or 10,000 Kelvin and Actinic (420nm). These are called 50/50 lamps. Some are actually 60/40, but you get the idea.


    Color - Color Rendition Index

    Color Rendition Index (CRI) is a really easy concept. A light with a CRI of 100 makes anything looks exactly like it would outside a clear sunny day (100% daylight). Anything with too much or too little of any color gets a lower CRI. A good daylight lamp will have a CRI in the mid to high 90's. Most "Cool White" fluorescent lamps fall in at about 80 CRI. Think about that steel grey shirt you bought at Macy's and how it really looks green in sunlight. The lights in Macy's would have a low CRI.

    Brightness - Lumens and PAR

    That's it for the color of light, but we still need to describe how bright the light is. This is a little more involved, but I can make it simple and provide references for you to look up the details. There are 2 common scales that are used when measuring aquarium lights: Lumens and Photosynthetic Available Radiation (PAR). Lumens measure how much light we think we see. PAR actually counts the photons of electro-magnetic energy between 400 and 700 nanometers. The 2 things you need to know about both of these is that the higher numbers are brighter, and it's easier (cheaper) to create orange light than it is to create the same amount of blue light. For reference:

    A typical 100 watt incandescent light bulb (3000K) is about 1500 Lumens
    A typical 40 watt (4ft) fluorescent lamp (6500K) is about 2800 Lm
    A really good 250 watt daylight (6500K) metal halide lamp is 13500 Lm
    A really good 250 watt 10,000K metal halide lamp is 11000 Lm

    PAR is also sometimes called PPFD (Photosynthetic Photon Flux Density). Both are measured in microEinstiens/m2/sec (not that you care). To accurately measure PAR, you need a light meter that costs a few thousand dollars, so not too many people do that. There are cheap alternatives available for a few hundres dollars, but they are usually less sensative in the blue and purple spectrum that we care about in reef lighting - although they are better than nothing...

    Most fluorescent and metal halide aquarium lamps have what they call a burn in period. This is usually in the first 100 hours of use where the light is up to 20% brighter than normal and possibly a slightly different color. The light output levels off and starts slowly decreasing in brightness after the first 100 hours. The color slowly shifts away from the blue end of the spectrum and towards the orange and red end of the spectrum over the life of the lamp.


    Brightness and Distance

    Both measures of brightness are affected by how far you are from the light source (unless it's a laser). Think of looking into a 100W lamp from 6 inches away versus from across your back yard. Thatís a big difference. You can actually calculate the difference. Get a measurement of how much light hits a sheet of paper from 1 ft away. At 2 ft, you'll have 1/4 as much light hitting that paper. A majority of the light is hitting the paper at an angle. The farther away you are, the more light misses the paper.

    Try this:
    1) Get a 12" diameter Frisbee.
    2) Draw a 6" diameter circle on your Frisbee and stand at 1 ft away from the light.
    - Inside that 6" circle is all the light that will hit your Frisbee when you stand 2 ft away from the lamp.
    - That's 1/4 of the total surface area of the Frisbee, thus 1/4 of the total light.
    3) Move to 2 ft away.
    4) Now, inside that 6" circle is all the light that will hit your Frisbee when you stand 4 ft away from the lamp.



    This is sometimes called the "inverse distance squared" rule and was acrually used by Newton's laws of gravity. At 1 ft, you have your baseline Ė letís say 1000 Lumens. At 2 ft, you take your baseline number divided by the distance squared, so 1000/(2*2) = 1000/4 - 250 Lumens. From the example above, at 4 ft: 1000 /(4*4) = 1000/16 = 62.5 Lumens.

    This decrease in brightness is not really because your distance just doubled, although that is a convenient way to calculate it. It's really because the light emitted from the lamp is actually coming off in all directions (again, unless your source is a laser), and the further you are form the source, the smaller the amount of light off that source that can hit your Frisbee.

    So, the higher the light is above the tank, the more surface it can cover. The closer the light is to your tank, the brighter a given chunk of surface under that light will be. Of course, this doesn't count the effect of using a good reflector. We'll get into that a little later.

    FYI: The human eye is a horrible instrument for judging light levels. :shock: Just put a 100 watt lamp on an extension cord. Go into your closet for 2 minutes... That's bright!! Now, immediately walk outside on a clear, sunny day while still holding the lamp. Doesn't seem so bright anymore, huh? The problem is that our iris adjusts and creates "relative brightness". The reference I remember (but can't relocate) is that the human eye adjusts so well that you need 2 lights right next to each other with greater than a 30% difference before it's clear to everyone which is brighter.
    9 to 5 sounds like a good night in Buenos Aires to me!!!

    Comment


    • #3
      Part 2 - AQUARIUM LIGHTS

      So by now, most of you are wondering what the heck all that has to do with your aquarium. Well, don't fret; this next section is more relevant to your fish tank without all the high school physics...

      Today we have more options than ever in the realm of aquarium lighting. Here are the most common:

      Incandescent lamps
      Incandescent lamps are still used over some small aquaria. I have a 5 gallon acrylic tank with a 5 watt incandescent bulb in the hood. Most incandescent lamps have a rated life of about 2000 hours or less. Incandescent lamps are very inefficient compared to newer technologies and are not available in the desired color temperatures (Kelvin) for aquaria, although you can get tinted light bulbs with drastically reduced output.

      Fluorescent lamps
      Normal Output (NO) Fluorescent lamps are the standard lighting you get when you buy a tank "combo" from a store. These come in 2 common sizes: T8 and T12. These numbers stand for how many 1/8ths of an inch the diameter of the lamp is. So, a T8 lamp is 8/8ths of an inch in diameter, or 1 inch. Similarly, a T12 lamp is 1.5" in diameter. These lamps are about 5 times more efficient than Incandescent, and are available in a wide range of color temperatures that are suitable for aquaria. Standard fluorescent lamps are rated for anywhere from 10,000 to 20,000 hours of use, but due to changes in color and brightness during the life of the lamp, these should be used for about a year at most.

      PC Fluorescent
      Power Compact (PC) Fluorescent lamps are very popular because they are small diameter (less than 3/4") tubes that are usually bent into a "U" shape. This way a 2ft U shaped PC lamps puts out about as much light as a 4ft T8 or T12 lamp. This is really handy when you have a smaller fish tank that needs a lot of light, but can't fit a 4 ft tube over the tank. These lamps are about 5 times more efficient than Incandescent, and are available in a wide range of color temperatures that are suitable for aquaria. PC lamps are rated for up to 10,000 hours of use.

      VHO Fluorescent
      Very High Output (VHO) Fluorescent lamps are a the same size as standard T12 fluorescent lamps, but are built to handle higher wattages. With most fluorescent technologies, the more wattage you apply, the brighter the lamp burns. However, more wattage usually wears the lamp out faster. You can actually overdrive a normal output fluorescent to burn as bright as a VHO, but the lamps will burn out significantly faster. A 4 ft VHO lamp is rated to handle 110 Watts compared to a 4 ft normal output lamp which uses 40 Watts or a 4 ft T8 that uses 32 Watts. Again, these lamps are about 5 times more efficient than Incandescent on a light output per watt basis, and are available in a wide range of color temperatures that are suitable for aquaria. VHO lamps are rated for 6000 to 8000 hours of use. Depending on the ballast you use, you can get anywhere from 6 months (magnetic ballast) to 2 years (electronic ballast) of actual use out of the lamps.

      T5HO Fluorescent
      T5's are the latest fluorescent technology. They are High Output, so the wattages fall between Normal Fluorescent and VHO. T5's are a linear bulb like T8's as opposed to U shaped PC's. The neat thing about these lamps is that they are so skinny (5/8") that they can be used with ultra efficient reflectors. T5's are popular in Europe, and are quickly gaining a in popularity in the USA. The lamps themselves are still just 5 times more efficient than Incandescent, but when coupled with the special reflectors, they can put 15-20 times more light into your tank than the equivalent wattage of incandescent bulbs. We'll talk more about reflectors later on... These are also available in a wide range of color temperatures that are suitable for aquaria. Most T5 lamps are rated for up to 20,000 hours of use. They daylight lamps are useable for up to 3 years. Actinic and "blue" lamps are said to be good for 18 to 24 months.

      Metal Halide
      Metal Halide lighting is very popular with coral reef keepers. These lamps have a small bulb that is about 1" in diameter. This bulb is filed with mercury and other metals. When enough electricity is applied across the bulb, a plasma arc forms and causes the metal compounds to glow. Compare putting 160 watts across a 6 ft VHO lamp to putting 175 watts across a 1" halide bulb. You get about the same number of Lumens, but the halide is much more compact. Actually, halides are less efficient at creating Lumens, but more efficient at creating PAR than fluorescent lamps. Metal Halide lamps are rated for 6,000 to 12,000 hours of use. Plan on using them for about 1 year per lamp.

      Aside from being an efficient source of PAR, halide lamps also behave like a point source of light. That means that they mimic the sun and can create "shimmer" lines in your tank if there's enough surface agitation.

      Also, note that metal halide lamps can get extremely hot, since all the energy of 12 ft of VHO (or 32 ft of T8 ) is packed into 1 cubic inch in a 250W halide. It's also dangerous to look directly at a halide lamp for more than a glance. Many halide lamps can emit hazardous UV-C rays and some should only be used with a protective glass UV sheild. Due to the size and composition of the outer glass envelope, Mogul based lamps are considred safe from UV-C, where Double Ended lamps require an additional glass sheild.

      LED Lamps
      Lately, Light Emitting Diodes have been getting brighter and brighter. LEDs also have the advantages of being extremely efficient and up to a 100,000 hour life expectancy, so you shouldn't have to replace them very often - if ever. The downside is that getting enough LEDs to illuminate a tank is still an expensive proposition when compared to most of the other lighting technologies available.

      Skylights & Greenhouses
      What could be better than natural sunlight? You have to consider the seasonal variations in light for different latitudes (about 2x as much light on average in summer as winter in Ohio), a dark tank at night, and you're locked into a 6500K color temperature unless you filter the light. If you can live with those issues, solar lighting has a few benefits:

      1) Long term savings
      Consider that it's about $300-$500 for a DIY Tube skylight kit from your local home improvement warehouse. That's about the same price and same light level as a 250W metal halide pendant system. Now consider that you have ZERO electrical cost for the skylight, but about $50 per year to keep the halide going + $50 for a new lamp every year. Some manufacturers even make tubular skylight kits that are dimmable so you can adjust the light level to your own preference.

      2) Free moonlight
      Is the lunar phase the key to spawning certain corals and fish? Who knows, but natural moonlight can create a neat evening effect in your tank.

      The Catch:
      Varying light levels (duration and intensity) seasonally and based on local weather. Fixed 6500K. Essentially, in Ohio our winter days average about 10.5 hours, while summer averages over 14 hours per day of daylight - with the light also being more intense in summer. In the tropics, light levels are more even throughout the year, and the days vary from about 11 to 13 hours of average daylight.

      You can change the 6500K color temp of daylight by using a "theatrical film" that will filter some wavelengths to give you the desired color
      9 to 5 sounds like a good night in Buenos Aires to me!!!

      Comment


      • #4
        Part 3 - EFFICENCY

        This part of the article might actually save you money, so pay attention!!

        Lamp Efficiency
        This is fairly simple - you take the Lumen output of a particular lamp and divide by how many watts that lamp uses to make those lumens. You can do the same thing with PAR if the numbers are available.

        The interesting thing is that there is not an easily explained direct relationship between PAR and Lumens. Many fluorescent lights are more efficient at creating Lumens. At the same time, metal halide lamps still do a heck of a job with Lumens, but are more efficient at creating PAR.

        Here are some numbers to compare Lumens:
        100W Incandescent Lamp 1600 Lumens = 16 Lumens/Watt
        250W 6500K Metal Halide 13500 Lumens = 54 Lumens/Watt
        65W Power Compact 4550 Lumens = 70 Lumens/Watt
        40W Fluorescent (4ft) 2880 Lumens = 72 Lumens/Watt
        110W VHO Fluorescent(4ft) 8000 Lumens = 73 Lumens/Watt
        54W T5 HO Fluorescent(4ft) 4750 Lumens = 88 Lumens/Watt

        Ballasts
        Now it suddenly gets a little more difficult... The lamp itself is not the only thing that sucks down electricity. The ballast used to drive the lamp is a big factor. Suppose you have a 175 watt metal halide system. The ballast that drives that lamp can consume up to 200W of electricity. The difference between what the ballast consumes and what it delivers to the lamp is given off as heat by the ballast. As much as 10-20% of the energy consumed by magnetic ballasts may be wasted as heat, but there is another option... There are a number of electronic ballasts available for fluorescent and halide lamps that are up to 98% efficient. These typically cost more than the magnetic ballasts, but can save money in the long run if your electricity cost is high...

        Reflectors
        This is HUGE!!! One of the biggest factors in efficiency of a lighting system is the reflector. A well designed reflector sends all the light that was going out the sides and top of the lamp back down into the aquarium. With that in mind, the smaller the lamp, the easier it is to design an efficient reflector. With a smaller lamp, the reflector can easily direct light down without hitting the lamp again - a concept known as re-strike.

        That's why the 98% reflective, parabolic reflectors for T5 lamps can direct 350% more light into an aquarium than the bare lamp can, while the gloss white reflectors of T8 shop lights typically direct 75% more light into an aquarium than a bare lamp.

        Metal halides have a similar phenomenon. Single ended (SE) halide lamps have a large screw base, like a normal light bulb, but bigger. The outer glass area of these lamps can be 2+ inches in diameter, and 8 inches long. Double ended (DE) halide lamps fit into sockets similar to the way that halogen work lights do. The whole lamp is about 1 inch in diameter and 5 to 6 inches long. The reflectors for the DE lamps have proven to be so efficient that a 250W DE halide in a good reflector can come close to the light output of a 400W SE halide in a not-so-good reflector.

        Still, with recent advances in SE halide reflectors, it's hard to compare SE to DE because most SE lamps simply produce more raw light (has to do with having a larger inner lamp and better heat dissipation) - and do not need the extra glass sheild that can lower PAR output up to 10%.

        The lesson here is that with a good reflector, you may not need as many lamps, or at least you could use lower output lamps. This can help save on the lamp replacement cost, and the electric bill.

        The skinny is that if you use a flat mirror as a reflector, you get a 20% increase in light. If you use bent metal in a parabolic shape you can get a 125-150% increase in light using standard polished aluminum, or even high gloss white paint. If you use a specially made "secular aluminum" parabolic reflector, you can get a light increase of 250-350% in many cases. Finally, if you used one of the newer 4-sided parabolic reflector (Lumenarc, LumenMax, etc). you get even greater efficency.

        Notice that I haven't said anything about "watts per gallon". That's because "watts per gallon" is a really crappy way to determine light for a tank. With the huge differences in efficency created by various lighting technologies utilizing different ballasts and reflectors, this is really useless.

        Here's a perfect example:
        When the initial studies of 250W DE pendants versus 400W SE pendants came out, I held a reef club meeting at my house where a buddy brought his 400W SE setup to compete with my 250W DE setup - both using Ushio 10K lamps. I started quoting Sanjay Joshi's article where he says that the DE setup should give about 90% of the light while using only 70% of the power.

        Of course, my buddy was all ready to gloat when his setup crushed mine, but when we turned them on, my setup (250W DE Ushio + ReefOptixIII + IceCap ballast) completely blew away his setup (400W SE Ushio + PFO retro + PFO standard ballast).

        I couldn't explain it. I was baffled. All the existing data said that they should be so close that nobody should be able to see a difference with their naked eyes (which need about a 30% difference to pick an obvious winner) - and that was with the higher output magnetif HQI ballast... I was using the lower output electronic ballast, yet the 250W setup was obviously TWICE as bright!!!

        It turned out that my buddy never removed the protective blue film from his reflector, and over the past few months it had turned brown and basically welded itself to the aluminum. When we replaced the bad reflector with another retro that I had laying around, we got the expected result - that you couldn't really tell the difference with your eyes. The 400W looked a hair brighter than the 250W electronic setup, but it was too close for a real judgement call.

        So the point is that watts per gallon is a completely useless means of measuring light output with all the other factors effecting the efficency of a lighting system.
        More ways to save money

        Under the right conditions, I'm a big advocate of light movers. I currently use 4 x 250W HQI pendants to illuminate a primarily SPS tank with a surface area of almost 4 ft X 7 ft. Since my corals only occupy about 3 ft X 6 ft, I have all 4 halides on a beam, parallel to the front of the tank. That whole beam moves about 24-30 inches from front to back to allow 4 halides to cover an area that really requires about 8 pendants.

        Granted, I can't compare to how my corals would have done had I actually used 8 pendants... Still, I'm satisfied enough that my next move is to switch to 2 x 400W pendants using parallel and perpendicular light movers to cover my whole tank - in addition to a single 250W pendant to add a 3 hour mid-day bump in total light levels.

        If you're considering light movers, here are the pros and cons:

        PROS:
        - replace an XXX wattage lamp with a 5 watt motor
        - less lamp replacement cost
        - About the same equipment cost as a pendant and ballast
        - some funky light and shadow patterns that some people enjoy
        - different incident angles that light hits your corals

        CONS:
        - some funky light and shadow patterns that some people may not like
        - really only increases coverage from about a 2'x2' area to a 2'x3' area with a single rail

        If you're really considering these, plan on 2 lamps on a mover as an equivalent replacement for 3 stationary lamps. You can get away with 1 halide on a mover replacing 2 stationary lamps, but the shadows would be excessive (in my opinion).
        9 to 5 sounds like a good night in Buenos Aires to me!!!

        Comment


        • #5
          Part 4 - APPLICATION IN THE REEF AQUARIUM

          Fish Tanks
          For fish only aquaria, the light is really just for you to watch the fish (as opposed to growing plants or coral), so you can choose whatever color temperature you prefer. My favorite combination is 10,000 Kelvin and 50/50 flourescent lamps. It still looks like crisp white light in the tank, but the blue and green pigments in the fish really POP with the addition of 50/50 actinic lighting. Normal output fluorescent, and PC lighting is adequate for most fish only tanks. You don't really need the extra output of VHO, T5 or Metal Halide unless you have a really huge tank to illuminate. Of course, if you have algae eaters, you may want more light to grow the algae.

          The bonus of metal halides on fish only tanks is that the tank looks REALLY COOL. I used two 250W halides in the 14K color temp range (blue-ish) to illuminate my old 200 gallon fish tank, and I really liked it. Granted, 175W lamps would have been plenty, but I had the 250's handy. What you get with the metal halides is a simulated point source of light. Point source lighting plus surface ripples in the water creates the same "glimmer lines" that people associate with scuba diving or shallow tropical waters.

          I also like arranging my lights to create the illusion of more tank depth. Put the brighter and whiter lights (6,500 and 10,000 Kelvin) toward the front of the tank. Put the darker and more blue lights (50/50 and actinic) toward the back of the tank. I did this on my 200 gallon tank using 10K lamps on the front and actinics across the back, and it leaves you thinking that the tank was extra deep.

          Coral Tanks
          I could get in a lot of trouble here, so I'll make a disclaimer right off the bat... Do your own research before you buy. See what others are using with similar livestock.

          Generally, for Softies and most LPS, you can get by very well with PC, VHO, lower wattage Halides, and fewer T5HO's that you'd run on an SPS tank. I have a friend who only uses two 14,000 Kelvin 70W halides in DIY pendants on a 90 gallon LPS tank, and everything looks very healthy. I have other friends with 2 x 400W halides over a 300 gallon LPS tank, and everything looked great.

          From measurements I've made, most LPS tanks can do well with PAR levels around 50-100 using the cheap Apogee PAR meter. 100 PAR is not the upper limit by any means, and most LPS will benefit from more light - just take time to acclimate them.

          For most SPS to thrive, you want PAR levels above 100 - preferrably about 200 PAR. Some of the best lit tanks I've measured had light levels of 100-150 PAR at the sandbed - 30" below water. These same tanks had light levels approaching 800 PAR just below the water surface.

          One thing to note if you're planning for a specific PAR level is that total light drops by about 33% in the transition from above to just below water. You can't avoid it unless someone figures out a really slick way to stop water from reflecting 1/3 of the light back into the air. Granted, you can enclose your whole canopy and line it with mirrors or reflective mylar. That might recover 1/2 of the light that was being wasted if you're lucky - probably less, but it's better than nothing...
          9 to 5 sounds like a good night in Buenos Aires to me!!!

          Comment


          • #6
            References & great Links...

            References:

            http://imagine.gsfc.nasa.gov/docs/sc...mspectrum.html

            http://www.windows.ucar.edu/earth/At...re/kelvin.html

            http://www.advancedaquarist.com/issu...03/feature.htm

            Ohio Solar Radiation Levels
            http://rredc.nrel.gov/solar/pubs/redbook/PDFs/OH.PDF

            Links:

            Sanjay's Reef Lighting Info & Article Index
            http://www.reeflightinginfo.arvixe.com/

            JBNY's 250W SE Halide Lamp Comparison
            http://www.cnidarianreef.com/lamps.cfm

            Note: The Sanjay's and Joe's numbers were measured with different instruments from different distances, so don't compare them to each other...

            If you have any other great lighting links that I haven't included, please PM me and I'll add them.
            9 to 5 sounds like a good night in Buenos Aires to me!!!

            Comment


            • #7
              Here is Sanjay's comparison site. There is an area where you can plug in your wattage, bulb type, ballast type, etc. and get some great info.

              http://www.manhattanreefs.com/lighting
              PEACE.....from Zeppelin

              Comment

              Working...
              X