Of all that goes into configuring a viable (to optimal) saltwater set-up, nothing is more poorly understood or hotly debated amongst hobbyists than lighting. Judging by the queries we receive on WetWebMedia.com, and exhaustive visits experiencing said systems in person, there are large gaps in people's understandings of what their options are, the gains/losses to be had in efficiency/results, and indeed, simple actions they might take to improve on what they have invested.

            Here I am going to undertake to list and explain the principal elements of applied lighting'¦ including general categories of fixturing, the range and use of light by photosynthetic life forms hobbyists may keep, a go at having you determine what it is you want to do with this life, and the aforementioned 'things you can do' to improve results from your costs in gear and ongoing electrical consumption.

Is There ONE Perfect Lighting System'¦ As in the BEST?

            Mmm, no; there's not. GIVEN a tank of certain dimensions, a selection/mix of livestock, a budget for initial set-up and ongoing costs of operation, your subjective evaluation of what is beautiful, AND an idea of what you're trying to do with your livestock'¦ grow it maximally, have it be the most colorful... there are still a range of choices. Be that stated, some general 'rules' to consider as guidelines:

Costs of Lighting vs. Useful Photonic Energy

            The cheapest type/source is 'none at all''¦ i.e. either just incidental insolation (sunlight) or the use of non-photosynthetic life. Though many of the 'corals' (sensu dictu of hobbyists) are photosynthetic (along with many sponges, some molluscs like Tridacnids, other groups'¦), there is a huge range of not-much to fully non-photosynthetic soft, hard et al. 'corals' that can/do quite well w/o supplementary light.

            For the sake of our keeping captive aquatics though, our being visually-oriented beings ourselves, almost all captive systems will be artificially illuminated. What is at question is what to use, how expensive it will be to buy and run, and what sorts of effects the lighting will have. There are a few standard choices of fixtures with options as to lamps/bulbs, ballasting, timers and more.  

Photosynthetic Life: Definition, Differences, Adaptability

            Organisms that can/do use light energy to form useful foods are labeled photosynthetic life or photosynthates. The compounds these organisms use for converting light energy to chemical changes are most often termed photosynthetic pigments; these pigments are generally contained within endosymbiotic algal life called zooxanthellae.

            There are several types of said photosynthetic pigments (Chlorophylls , Carotenoids et al.), of differing make-up, each with a determined range of utility, given the wavelengths and photo-strength of light it receives. These pigments, like the cells, organelles that contain them, are not static in their content, but can be and are made and lost to 'fit' given conditions.

Is More Light (Intensity) or Higher Kelvin or Spectrum More Important?

            A bit of all these measures of light quantity and quality are important; no one more so in the absence of the others. The Intensity, most often discussed in terms of wattage (a measure of electrical force, consumption) may be inadequate to overbearing (see below). The analogy of having enough 'power' to drive a mechanism is apt, but not so much as to 'bust it'.  Of importance is not whether one needs so many 'watts per gallon' but how many lumens per watt one is getting per watt consumed, delivering to ones livestock with a given, appropriate light source; using a moderate amount of power.

            Kelvin, a measure of light radiated relative to the temperature of a black body source, is much over-discussed in the aquarium interest. Functionally, as one might presume, Kelvin temperatures similar to our sun's production measured at reception (5,600-6,400 K) are most useful. The higher Kelvin lamps (10k, 20k'¦K) being more for appreciation (i.e. 'looks') by/for aquarists rather than utility unless your tank is (for hobbyists) very deep. In cases where light-using life will be in 24-30 or inches more of water depth, higher Kelvin ratings (8-10k) may be desirable. It should be mentioned that employing higher K lighting can also result in higher RedOx, improved overall system and livestock health as well.

            Spectrum is important. Many types of lamps/fixtures produce light that is of little use to submerged photosynthetic life. As stated above, the actual pigments involved in the process/es of photosynthesis are able to best utilize light w/in certain (received) spectral wavelengths. PUR, Photosynthetically Useful Radiation (400-560 and 620-700 nanometers) being ideal.

Light Fixtures: Cost Per Function Up Front and Ongoing:

            Presently there exists a direct relationship between cost of acquisition and operation of light fixture types as a function of their production of useful photonic energy'¦ Incandescents, T-12s (e.g. 'shop lights'), High/er Output Fluorescents, Compact Fluorescents, SHO, VHO T-5's on down, HQI/Metal Halides and evolving LED technologies  in order all make less to more PAR per dollar spent on their fixtures and electrical consumption. This is however not the end of factors to consider in choosing one way of lighting over another. Currently, HQI/Metal Halides are best at 'punching' light to depth (over 24' of water let's say), and still further consideration must be given to consequences of using light sources due to their production of waste heat and sometimes undesirable UV wavelengths of light'¦

            And even this isn't the end of co-factors one need contend with. IF over-driving photosynthesis is desired, achieved, other aspects of metabolism must be handled in concert'¦ The 'law of the minim' states that there is always some aspect, some rate-limiting step to every reaction series. Should light itself not be this rate-limiter, alkaline reserve, biomineral lack, perhaps other forms of chemical (e.g. Carbon, Nitrate, Phosphate)  or biological food will be.

Blue/Actinic Light Efficacy/Utility: An Effort At Describing & Rating

            More for looks than function, the lower end spectra (400 ish nm) that is the target/range of this lighting is often touted as being necessarily supplied by special lamps'¦ This is assuredly not the case; as enough of these wavelengths are almost always produced by other sources'¦ However, if you're determined to use such lamps (though your system, livestock would be better off using just more 'white light''¦) you are encouraged to utilize timers, having the 'blue light' come on and go off a half to full hour ahead of the 'regular' lighting. 

Can There Be Too Much Light?

            Yes'¦ for light-using life in the acclimated and sustained sense, there is the issue of saturation. A point in which more light does no more good (driving electron transfer'¦) and may harm the organism. Maximum lux (a lumen per square meter, a measure of light intensity'¦ determined by a meter), should be no more than that of the wild reefs (110,000-120,000 lux at the surface, about 20,000 to 25,000 lux at a meter of depth'¦), this light being of useful wavelengths (PAR: Photosynthetically Active Radiation'¦ light between the wavelengths of 400-700 nanometers.

What (Mal) Affects Light Transmission & Usage?

1)      Dissolved color can be a very important reducer of light transmission. These losses can exceed 10-20% of possible production. Using a good grade of activated carbon on a punctuated basis, assuring high RedOx potential is useful for reducing color.

2)      Suspended particles and bubbles likewise can block light'¦ They can be eliminated through sieving out such through mechanical filtration, arranging for bubbles to coalesce, be popped or removed from the main/display tank.

3)      Dirty lamps and tops can also be a major source of light loss. A good idea to add their cleaning (before lights on) on your weekly cleaning schedule.

4)      Reflectors can greatly add to your lighting efficiency. Do look about for reports on the best available to direct light output down, into your system.

5)      Old lamps/bulbs. They may still 'look bright' but lumen depreciation (6-9 mo.s bulb life in general for ½; LEDs last much longer) and spectral drift with time/use render all lamps/bulbs less and less useful. Mark their inception date in your log-book, list of aquarium facts, and switch them out on schedule.

6)      Backgrounds can be important. Take care not to adhere them too closely to backs and sides of tanks, as the light 'bouncing' from the interface twixt your glass or acrylic and the background (rather than air) can greatly reduce total light availability.

7)      Organism placement in the water column is extremely important, particularly for 'wild-collected' stocks. By and large, the highest light-using life should be placed as close to the surface as practical; with lower use species being set minimally deeper. Here I will mention the importance of 'light acclimation' of reef-collected specimens'¦ they are best kept in increasingly 'brighter' circumstances while being quarantined

Cloze:

So, what is the 'right' or even perfect lighting system, choice? It depends'¦ on the types of life you keep/intend, what you hope to have them do (growth, color, reproduction'¦), what you have to spend up front on gear (fixtures, lamps/bulb, possibly fans/chillers), ongoing for electricity, and do degrees your desire/tolerance for 'fooling' with all this. Think on what has been stated above'¦ and be conscious when choosing your system'¦ size, shape'¦ and determining (through planning and action) what life forms you will keep, what you have in mind for expression'¦ Thorough-enough investigation of ones choices, short and longer term, the cursory use of light metering, care to maximize ones results per cost should be customary practice.

Bibliography/Further Reading:

Joshi, Sanjay, 2006. Facts of Light. http://www.reefkeeping.com/issues/2006-05/sj/index.php

Riddle, Dana  & Miguel Olaizola, 2002. Lighting the Reef Aquarium - Spectrum or Intensity?, http://www.advancedaquarist.com/2002/2/aafeature

Strohmeyer, Carl, 2009. Aquarium Lighting. http://www.americanaquariumproducts.com/Aquarium_Lighting.html

Small Marine Aquariums Book 1: Invertebrates, Algae New Print and eBook on Amazon: by Robert (Bob) Fenner	Small Marine Aquariums Book 2: Fishes New Print and eBook on Amazon: by Robert (Bob) Fenner	Small Marine Aquariums Book 3: Systems New Print and eBook on Amazon: by Robert (Bob) Fenner